Levin The Earth Through Time 10th c2013 txtbk

Placental Mammals b 535

FIGURE 16-52 Restoration of Moeritherium. (A) Head. FIGURE 16-54 Four-tusked mastodon, Late Miocene/
(B) Skull. Early Pliocene. The mounted skeleton is in the collection of
dinotheres (Fig. 16-53). The tusks of dinotheres were the Denver Museum of Natural History. (Harold Levin)
distinctive in that they were present only in the lower
jaws and curved downward and backward, an orienta- the second incisors in both the upper and the lower
tion useful for uprooting plants and digging for roots jaws had developed into tusks.
and tubers.
By Miocene time, a larger proboscidean named
Another branch of the proboscidean family tree Gomphotherium arrived in North America via the
produced mastodons and elephants. Palaeomastodon, Bering isthmus into Alaska. Subsequent proboscidean
in the Oligocene of North Africa, probably was rep- evolution produced a variety of long-jawed masto-
resentative of the group from which true mastodons dons, some with lower jaws almost 2 meters (6 feet)
evolved. The skull was long, the trunk was short, and long.

FIGURE 16-53 Skull of Dinotherium, a Miocene The most bizarre proboscidean was the “shovel-
proboscidean. The tusks in this odd-looking proboscidean tusked” Amebelodon (see Fig. 16-49A) of the Pliocene.
were curved down and backward like some sort of farming Tusks on its lower jaws were flattened, forming two
hoe. Skull length is about 1.2 meters. (Harold Levin) sides of a broad, scooplike, ivory shovel. Mastodons
with shorter jaws and massive tusks (Fig. 16-54) were
common throughout North America during the
Pleistocene and survived until comparatively recent
times.

MAMMOTHS (ICE AGE ELEPHANTS) “Mammoth”
loosely applies to Ice Age elephants of North America,
Europe, and Africa. In their molar teeth, the cusps of
earlier forms have merged to form transverse ridges
of enamel (Fig. 16-55). The teeth also were higher-
crowned and extended deep into the jaws.

Mammoths were a magnificent group of animals
that included the famous woolly mammoths (Fig.
16-56) drawn by our own ancestors on the walls of
their caves. The great imperial mammoth reached
heights of 4.5 meters (15 feet) and ranged widely across
California, Mexico, and Texas. The Columbian
mammoth had immense spiral tusks that in older
individuals overlapped at the tips, becoming useless
for digging purposes.

Late Pleistocene proboscideans were hunted by
humans. Then, about 8000 years ago, all but the
African and Indian elephants became extinct. Their
continued survival will depend on our good judgment
and that of the governments that control their habitats.

536 c Chapter 16. Life of the Cenozoic

ENRICHMENT

How the Elephant Got Its Trunk The elephant got its trunk by hypertrophy of the nose and
upper lip. But why?
Among the most interesting mammals to evolve during the
Cenozoic are the proboscideans—mastodons, gompho- When we view the bones of proboscideans—beginning
theres, and mammoths—so-named for their most distinctive with the relatively small and primitive groups of the Eocene
feature, their prominent trunk. The elephant’s trunk is a through the giant Pleistocene mastodons and mammoths—
muscular, much-elongated organ containing nostrils that we can see several trends. One obvious trend was the size
extend through its entire length to the tip. How did this increase, of both the body and huge proboscidean head.
remarkable appendage develop? Supporting the weight of the ponderous head required a
short, powerful neck. As proboscideans grew taller, reaching
In Rudyard Kipling’s story The Elephant’s Child, an overly food at ground level with a short neck would have been
inquisitive baby elephant tries to find out what the crocodile difficult. Natural selection paralleling that of the large head
had for dinner. When the baby elephant lowers his head and short neck resulted in the development of the trunk.
along the bank of the great, gray-green, greasy Limpopo
River, the jaws of the crocodile close on his nose. There The elephant’s trunk is a structural adaptation for feeding
ensued a fierce tug-of-war in which the baby elephant’s poor that could be used not only for raising food from the ground,
nose is stretched into the trunk we know today. but also for stripping leaves from branches and stuffing them
into the mouth. Along with the evolution of the trunk, the
Nice children’s story, but the elephant achieved its won- lower jaw became shorter, allowing the trunk to hang down-
derfully long, grasping trunk by other means: evolutionary ward. Tusks in the lower jaw that were present in early
processes that operated over many generations, resulting in proboscideans became smaller and gradually disappeared.
enormous elongation of the nose and upper lip. Scientists
call such extraordinary growth of a body part hypertrophy.

FIGURE 16-55

Cheek teeth in jaws of
(A) mastodon and (B)
mammoth. Paired cusps
of mastodon teeth were
used for crushing
vegetation, as we typically
see in browsing mammals.
The mammoth tooth, with
its parallel ridges of
infolded enamel,
resembled a bony
washboard. It was well
adapted for grazing on
tough grasses and cereals.
(Harold Levin)

Placental Mammals b 537

FIGURE 16-56 Woolly mammoth. In the Late Pleistocene, these magnificent Ice Age
elephants lived along the borders of the continental glaciers. Their remains have been found
frozen in the tundra of northern Siberia. (Painting by Charles R. Knight/Field Museum Library/
Getty Images, Inc.)

CETACEANS (WHALES AND PORPOISES) Among all In rocks only 10 million years younger, yet another
mammals, none have so completely adapted to life in ancestral whale named Ambulocetus has been found.
the sea as the cetaceans (whales and porpoises). When Ambulocetus (the name means “walking whale”) had
we see their sleek bodies moving through the water, it is webbed feet on its hind limbs and front flippers. The
difficult to grasp that these mammals are descendants of shape of its back vertebrae suggest it may have moved
the hoof-bearing artiodactyls! But this hypothesis has about on land with the up-and-down motion seen in
been confirmed by recent discoveries in Pakistan of a today’s seals. This motion may have been a sort of
55 million-year-old aquatic hoofed mammal that is preadaptation for the up-and-down tail propulsion
the direct ancestor of the first cetacean. The fossil has seen in modern whales.
ankle bones characteristic only of artiodactyls.
In Basilosaurus (Fig. 16-59) from the Late Eocene of
An earlier discovery named Pakicetus also had the Egypt, we get a glimpse of the trend toward giganti-
artiodactyl ankle structure. Pakicetus was a four-legged cism. This whale attained a length of 60 feet. Tiny
animal that probably ventured into streams, estuaries, hind limbs complete with toes were still present in
and lakes to feed on fish, about 50 million years ago Basilosaurus, but these rear limbs were small and too
during the Eocene. Except for whalelike character- weak to provide strong propulsion.
istics of its teeth and the ear region in the skull,
Pakicetus did not look at all like a whale, as you can Modern whales arose from the group that included
see (Fig. 16-57)! Basilosaurus and divided into two lineages: toothed
whales and whalebone (baleen) whales.
But the link between artiodactyls and whales also is
supported by DNA sequencing studies. As depicted on Toothed whales include modern porpoises, killer
the cladogram (Fig. 16-58), molecular biologists think whales, and sperm whales like author Herman
that hippopotami are closer to whales than any other Melville’s famous Moby Dick.
group of artiodactyls. The fictional Moby Dick was indeed an awe-
some beast. However, it was not nearly as fear-
FIGURE 16-57 Ancestral whale Pakicetus, Eocene of some as a fossil sperm whale named Leviathan
Pakistan. Because the remains of Pakicetus were found in melvilliei discovered in Miocene rocks in Peru.
stream-deposited sediments, it is doubtful that this primitive Measuring more than 16 meters from head to tail,
whale ever ventured into the open ocean. Except for this carnivorous super predator had teeth up to
whalelike characteristics of its teeth and the ear region in the 35 centimeters long, longer than those in T. rex.
skull, Pakicetus did not resemble a whale at all, as you can see.
(Reproduced with permission by Carl Buell.) Whalebone whales include the titanic blue whale,
right whale, humpback, gray, and Greenland
whale. These plankton-feeding giants first
appeared in the Miocene. Instead of teeth, they
possess ridges of hardened skin that extend down-
ward in rows from the roof of the mouth. The
ridges are fringed with hair, which entangles the
tiny invertebrates on which these cetaceans
feed—thus, the paradox of the largest of all
animals feeding on some of the smallest. The

538 c Chapter 16. Life of the Cenozoic

FIGURE 16-58 Cladogram of
major artiodactyl groups. This
diagram shows the close
evolutionary relationship
between artiodactyls and whales.

FIGURE 16-59 Eocene whale Basilosaurus.
The cetacean tendency toward increased size
already is evident in this early whale, more than
20 meters long (65 feet).

Summary b 539

FIGURE 16-60 Animals of
central Alaska about 12,000
years ago, during the Late
Pleistocene. Fossil remains of
this period are abundant. They
indicate a fauna in which grazing
animals predominated, with the
rest composed of browsers and
predators. (Courtesy of U.S.
National Museum of Natural
History, Smithsonian Institution,
J. H. Matternes mural)

great blue whales far exceed in mass even the Did global warming cause extinctions among large
largest dinosaurs, for some have attained weights mammals? At least in North America, the timing for
of over 135 metric tons (the weight of some climatic warming is appropriate, for the last glacial
locomotives). interval ended between about 12,000 and 10,000
years ago. However, why do we not find evidence
cDEMISE OF THE PLEISTOCENE of extinction during earlier interglacial intervals?
GIANTS Perhaps the most recent episode of warming was
more severe.
At the time of maximum continental glaciation approx-
imately 17,000 years ago, the Northern Hemisphere Were human hunters responsible for the extinc-
supported abundant and varied large mammals— tions? Humans roaming post-glacial terrains hunted
comparable to that which existed in Africa south of efficiently in highly organized social groups. They
the Sahara a century ago (Fig. 16-60). There were giant had advanced stone age weapons, and were capable of
beavers, mammoths, mastodons, elks, most species of skillfully bringing down even the mighty mastodon
perissodactyls, a variety of artiodactyls, and huge and mammoth. Many human sites are known that
ground sloths. include finely crafted spear points and butcher-
marked bones of the animals killed. Perhaps, even
Most of these large mammals maintained their num- as now, human predators may have killed in excess of
bers quite well during episodes of glaciation, but expe- their needs. As the large herbivores were decimated
rienced rapid decline and extinction in the period by hunters, carnivores experienced a depleted food
following the retreat of Wisconsinian glaciers. Extinc- supply and joined their prey on the path to
tions in North and South America were particularly extinction.
severe about 11,000 years ago. In Australia, the die-off
occurred about 20,000 years earlier. What caused the The two hypotheses for the extinction of large
extinctions? There are two hypotheses. One proposes Pleistocene land animals are not mutually exclusive.
that global warming brought vegetative changes and Many scientists today favor a synthesis of the two
seasonality detrimental to large herbivores. The second concepts, suggesting that climatic change coupled
hypothesis puts the blame on overkill by human hunters. with overkill by human hunters led to the demise of
many magnificent beasts of the Ice Age.

SUMMARY

The Cenozoic was a time of gradual change to present-day occurred as dense jungles gave way to deciduous forests,
conditions. The warm, humid climates common during parklike woodlands, scrublands, and grasslands.
much of the Mesozoic persisted into the early Paleogene,
but were replaced by cooler and dryer Neogene condi- Large discoidal foraminifera such as Nummulites were
tions. As a result, pervasive changes in land vegetation characteristic of areas in the Tethys Sea and the tropical
western Atlantic. Smaller planktonic foraminifera

540 c Chapter 16. Life of the Cenozoic artiodactyls (even-toed). Perissodactyls include horses,
rhinoceroses, and tapirs, as well as the extinct titanotheres
proliferated and underwent a marked diversification dur- and chalicotheres. Among artiodactyls, the large, piglike
ing the Cenozoic. entelodonts and smaller oreodonts failed to survive
beyond the Oligocene. However, living artiodactyls
Marine invertebrates of the Cenozoic generally were include swine, camels, hippopotami, and a diverse host
similar to those living today. Reef-building corals, mol- of ruminants.
lusks, echinoderms, and crustaceans were abundant.
Ungulates underwent specialization of teeth and limbs for
Teleost fishes, with skeletons composed almost entirely of grazing and running across relatively open plains. Gritty
bone, became varied and abundant. grass tends to wear teeth rapidly. To compensate, ungu-
lates evolved teeth with complicated ridges of hard enamel
Dinosaurs did not survive into the Cenozoic. But other and exceptionally high crowns.
reptiles—turtles, crocodiles, lizards, snakes, the tuatara,
and crocodiles—survived to modern times. The earliest proboscidean fossils were discovered in
Eocene beds of North Africa. Their radiation produced
Although the bird fossil record is poor, it is likely that an impressive array of variously tusked and specialized
most modern groups were present by Eocene time. Nearly mastodons and mammoths.
all continents seem to have had one or more species of
large, flightless, flesh-eating birds during the Cenozoic. The Pleistocene Epoch was a time of splendid diversity
among terrestrial mammals. The fauna probably was more
The Cenozoic is the “Age of Mammals.” During this era, varied and impressive than that of Africa a century ago.
mammals expanded rapidly into a multitude of vacated The Pleistocene also was an age of giants: colossal ground
habitats. From ancestral shrewlike creatures, either directly sloths, beavers over 2 meters tall, bison, huge mammoths,
or indirectly, the higher groups of placental mammals and woolly rhinoceroses.
evolved.
Widespread extinction was the dominant biologic theme
The adaptive radiation of Cenozoic mammals was remark- at the end of the Pleistocene. Either overkill by human
able. In addition to adapting to living on and in the hunters or climate change may have contributed to the
ground, mammals conquered the air (bats) and others demise of many giant Pleistocene mammals.
returned to the sea (whales, seals, walruses), where verte-
brate evolution had begun long ago.

Cenozoic herbivores with hoofs—the ungulates—include
two great categories: perissodactyls (odd-toed) and

arsinothere, p. 526 KEY TERMS
artiodactyl, p. 530
atoll, p. 509 mammoth, p. 535
barrier reef, p. 510 marsupial, p. 519
bovid, p. 534 marsupium, p. 519
brontothere, p. 529 mastodon, p. 534
carnassial teeth, p. 524 monotreme, p. 519
Carnivora, p. 525 myomorph, p. 524
castorimorph, p. 523 oreodont, p. 530
cetacean, p. 537 perissodactyl, p. 526
chalicothere, p. 529 placental mammal, p. 520
convergent evolution, p. 520 proboscidean, p. 526
Creodonta, p. 524 protorogomorph, p. 523
dinothere, p. 535 ruminant, p. 532
edentate, p. 521 sciuromorph, p. 523
entelodont, p. 530 scleractinid coral, p. 509
fringing reef, p. 510 scleractinid, p. 509
glyptodont, p. 521 squamate, p. 513
lagomorph, p. 524 teleost, p. 512
ungulate, p. 526

Questions for Review and Discussion b 541

QUESTIONS FOR REVIEW AND DISCUSSION

1. What water depth do reef corals prefer? How does water ichthyosaurs of the Mesozoic. What characteristics of
depth control coral growth? Explain the development of whales, however, are distinctly not reptilian?
atolls.
13. Horses, rhinoceroses, and tapirs are all odd-toed
2. Which groups of marine phytoplankton proliferated mammals belonging to a taxonomic group called:
during the Cenozoic Era?
___a. Perissodactyla
3. How did the cephalopod faunas of the Cenozoic differ ___b. Cetacea
from those of the preceding era? ___c. Artiodactyla
___d. Proboscidea
4. Which group of fishes is particularly characteristic of the ___e. Edentata
Cenozoic?
14. Cenozoic deep marine zooplankton fossils include
5. What evidence suggests that whales are descendants of many species of:
artiodactyls?
___a. Acritarchs
6. How might a paleontologist determine whether a fossil ___b. Scleractinid corals
lower jaw containing teeth belonged to a mammal rather ___c. Coccolithophorids
than a reptile? ___d. Oysters
___e. Foraminifera
7. What are ruminants? What advantages may be inherent
in the ruminant type of digestion? 15. An important bone used to identify a skeleton as
belonging to a bird is the furcula. This bone is also present in:
8. How is it possible to trace the development of the trunk
or proboscis in the skeletal remains of proboscideans when ___a. Certain Mesozoic theropod dinosaurs
the trunk itself is not preserved? ___b. Present in primitive monotremes
___c. Characteristic of extinct edentates
9. If evolutionary success can be measured in terms of ___d. Ungulates
diversity of a particular group of animals, how would you rate
perissodactyls compared to artiodactyls? 16. Carnassial teeth are a characteristic of:
___a. Lagomorphs
10. Prepare a list of changes that have occurred in horses ___b. Ruminants
during their Cenozoic evolutionary history. ___c. Proboscideans
___d. Carnivores
11. Describe the adaptations seen in Cenozoic herbivores
that are related to the spread of prairies.

12. Cenozoic whales demonstrate a remarkable example of
evolutionary convergence with the marine reptiles known as

17

A band of Neandertals returns from a successful
hunt. Not all Neandertals looked like those depicted here.
Fossils of Neandertals from Spain, for example, had
broader faces and lower foreheads as compared to their
counterparts living in colder northern parts of Europe.
(#Christian Jegou/Publiphoto/Photo Researchers,
Inc.)

CHAPTER 17

Human Origins

It walked on its hind feet, like something out of the Key Chapter Concepts
vanished Age of Reptiles. The mark of the trees was
in its body and hands. It was venturing late into a Primates evolved from small, arboreal, shrewlike
world dominated by fleet runners and swift killers. insectivores.
By all the biological laws, this gangling, ill-armed
beast should have perished, but you who read these Adaptations among early primates that were
lines are its descendant. important in the evolution of humans include
hands capable of grasping and manipulating
—Loren Eiseley, The Night Country, 1971 objects, an upright posture, stereoscopic vision,
and enlargement of the brain.
OUTLINE
c PRIMATES The two divisions of the Order Primates are the
c MODERN PRIMATES Suborders Prosimii and Anthropoidea. The
c PRIMATE BEGINNINGS Anthropoidea include humans, as well as
c THE EARLY ANTHROPOIDS monkeys and apes.
c THE AUSTRALOPITHECINE STAGE AND THE
Primate evolution began with the prosimians in
EMERGENCE OF HOMININS the late Cretaceous. Prosimians were common in
c THE HOMO ERECTUS STAGE the Paleocene and Eocene forests.
c BOX 17-1 ENRICHMENT: BEING UPRIGHT:
Australopithecines evolved primarily during the
GOOD NEWS, BAD NEWS Pliocene and were the ancestors of early members
c FINAL STAGES OF HUMAN EVOLUTION of the genus Homo.
c BOX 17-2 ENRICHMENT: NEANDERTAL OR
Homo erectus lived primarily during the middle
NEANDERTHAL? Pleistocene. Homo sapiens of the groups called
c BOX 17-3 ENRICHMENT: NEANDERTAL Neandertals and Cro-Magnon people lived
during the late Pleistocene.
RITUAL
c HUMANS ARRIVE IN THE AMERICAS Homo sapiens reached the New World by migrating
c HUMAN POPULATION: 7 BILLION AND across the Bering Land Bridge during glacial
stages of low sea level.
GROWING
c WHAT LIES AHEAD? The human population is growing at such a rapid
c SUMMARY rate that there is a danger it will exceed Earth’s
c KEY TERMS capacity to sustain it.
c QUESTIONS FOR REVIEW AND DISCUSSION
Evolution during the Cenozoic produced a large-
brained mammal capable of shaping and controlling
its own environment. That mammal was us: Homo
sapiens (Latin: intelligent human). Unlike previous ver-
tebrates, this remarkable creature profoundly changed
the surface of the planet, modified the environment in
ways both beneficial and destructive, and had such
pervasive effects on populations of other creatures as to
alter the entire biosphere. For these reasons, it is fitting
that the final chapter in our history of Earth examines
the evolution of humankind.

Homo sapiens shares many characteristics with other
members of the Order Primates to which we belong.

543

544 c Chapter 17. Human Origins

We resemble such primates as the great apes in basic
body structure and biochemistry. On the other hand,
we have become quite distinct from other primates in
many ways:

We have a larger, more complex brain.
We stand and walk erect, and we have structural

modifications of our vertebral column, legs, and
pelvic bones to make such erect posture possible.
Our face is flatter.
Our teeth are less robust.
We are capable of extraordinary manual dexterity.

These attributes have contributed to our ability to
conceive, manufacture, and use sophisticated tools.
Moreover, Homo sapiens exceeds all other primates in
intelligence, which has led to language, culture, and
aesthetic sensibility.

cPRIMATES FIGURE 17-1 Right hand of the Eocene prosimian
Primate Characteristics Europolemus. The hand shows key primate characteristics:
broad fingertips and an opposable thumb (the thumb can be
What traits qualify a mammal as a member of the Order touched to each of the other fingertips). Thus, the primate
Primates? This question cannot be answered easily, for lineage extends back in time about 50 million years.
primates are structurally generalized compared to most (Jonathan Blair/National Geographic Society)
other groups of mammals, which are specialized for a
specific diet, running, swimming, or burrowing. became positioned toward the front of the face so that
there was considerable overlap of both fields of vision.
Primate characteristics include a rounded head The result was an ability to see in “3-D,” or to see
shape, flattened face (especially when compared to depth—in other words, such eyes permit judging
most other mammals), and a brain that, relative to distance.
body size, is the largest of any terrestrial mammal. In
addition, primates retain the primitive number of five It would seem that grasping hands and feet and
digits (Fig. 17-1), have unspecialized teeth for eating good stereoscopic vision are obvious adaptations for
either plant food or meat, and never developed such an animal that leaps from branch to branch and seeks
special features as hoofs, horns, trunks, or antlers. In its food from precarious boughs. Yet many arboreal
the course of their evolution from shrewlike insecti- (tree-dwelling) animals such as squirrels, civets, and
vores, primates underwent many modifications of their opossums lack the short face, close-set eyes, and
hands, limbs, and thorax. Significantly, they also evolv- opposable digits. And they get along very well. For
ed binocular vision. Initially, these changes were this reason, anthropologists have recently suggested
adaptations related to life in trees and how food was that the visual attributes of primates originated as
obtained. Ultimatedly, they were critical to the evo- adaptations that allowed early insect-eating primates
lution of humans. to gauge accurately the distance to their prey without
movement of the head. By being able to grasp narrow
Snowball, the pig in George Orwell’s Animal Farm, supports securely with its feet, the animal was able to
remarked that “the distinguishing mark of man is the use both of its agile hands to catch prey as it flew or
hand, the instrument with which he does all his mis- scampered away.
chief.” Although it expresses a biased point of view, the
phrase is correct in suggesting the importance of the Claws are used by animals such as squirrels in
primate’s grasping hand with its opposable thumb moving about on relatively wide branches. They would
(Fig. 17-2). This characteristic not only permitted
primates a firm grip on tree branches, but also allowed
them to grasp, release, and manipulate food and other
objects. Rotation of the ulna and radius upon one
another in the forearm permits the hands to be turned
at various angles and even reversed in position.

The development of the hand was accompanied by
improvement in visual attributes. The eyes of primates

Primates b 545

not have been originally related to tree-swinging alone,
but to precision and safety in the capture of visually
located prey in the insect-rich canopy of tropical forests.

Other evolutionary modifications of primates were
related primarily to changes in the eyes and limbs. On
the outer margin of each eye orbit, a vertical ridge of
bone developed (postorbital bar) that protected the eyes
from bulging jaw muscles and accidental impact. As the
eyes became positioned more closely together, the snout
was reduced so that the face became flatter. In response
to a brachiating habit (swinging from branches), fore-
limbs and hindlimbs diverged in form and function, and
a predisposition toward upright posture developed.

FIGURE 17-2 Right hand of a human (palm up). The Primate Taxonomy or What’s in a Name
human hand is not used in locomotion. It can be used to
manipulate small objects between the fingers and thumb. Table 17-1 shows the two major primate groups: the
(The Primate Order Table, Copyright # 2000–2012 by Prosimii (tree shrews, loris, tarsiers), and the Anthro-
Dennis O’Neil, located at http://anthro.palomar.edu/primate/ poidea (monkeys, apes, and humans). The Anthro-
table_primates.htm) poidea is further divided into the Ceboidea (New
World monkeys), Cercopithecoidea (Old World mon-
not be as advantageous for climbing about on thin keys), and the Hominoidea (all apes and humans).
boughs and vines, and might not provide a sufficiently Informally, we call these groups hominoids.
secure hold for the quick catch of a moving insect. Thus,
it seems that binocular vision and the grasping hand may The Hominoidea can be divided into three families;
namely, the Hylobatidae (gibbons, siamangs), Pongidae
(orangutans), and Hominidae (African apes and hu-
mans). We can call these three families hominids.

TABL E 17- 1 Taxonomy for Apes and Humans

546 c Chapter 17. Human Origins

FIGURE 17-3 A young bonobo (Pan paniscus). (Adam FIGURE 17-4 A ring-tailed lemur. These primates are
Jones/Photo Researchers, Inc.) native to the island of Madagascar off the coast of Africa.
(Frans Lanting Photography)
Hominidae, in turn, can be divided into three sub-
families: Gorillinae (gorillas), Paninae (chimpanzees monkeys (Fig. 17-6). The Ceboidea, or New World
and the so-called pigmy chimps or bonobos shown in monkeys, are an early branch not involved in the
Figure 17-3), and Homininae. We informally dub the eventual evolution of humans. Included among the
Homininae as hominins. They hold special interest for ceboids are the spider monkey and marmoset, as well
you and me, as we are hominins. The subfamily, how- as the familiar little capuchin, or “organ-grinder mon-
ever, also includes all our ancestors of the genus Homo, key.” New World monkeys have flattish faces, widely
as well as their extinct fully bipedal ancestors. Thus, we separated nostrils, and prehensile tails that can be
have hominoids, hominids, and hominins, each with its wrapped around branches. Most are small in compari-
particular meaning. son to their Old World cousins. Their oldest remains
are found in Oligocene beds of South America.
cMODERN PRIMATES
Prosimii

The Prosimii are more primitive than the Anthropoi-
dea. For example, shrews (see Fig. 16-28) possess
clawed feet and a long muzzle with eyes on the sides
of the head. Lemurs, confined largely to Madagascar,
also have long snouts and lateral eyes, although more
to the front than those in the tree shrew (Fig. 17-4).
Some of the digits are clawed, whereas others have
flattened nails. The East Indian tarsier has a relatively
flat face (Fig. 17-5). As befits a nocturnal animal (feeds
at night), the eyes are exceptionally large and posi-
tioned toward the front to provide stereoscopic vision.

Anthropoidea FIGURE 17-5 Philippine tarsier (Tarsius syrichta). This
tree-dwelling prosimian has large, forward-directed eyes.
Monkeys are the most primitive members of the (Ron Austing/Photo Researchers, Inc.)
Anthropoidea. There are New World and Old World

Primate Beginnings b 547

FIGURE 17-6 Monkeys belonging to the Ceboidea
include the (A) spider monkey, (B) marmoset, and
(C) capuchin. ((A) Art Wolfe/Photo Researchers, Inc.,
(B) Jany Sauvanet/Photo Researchers, Inc., (C) Gregory
G. Dimjian/Photo Researchers, Inc.)

The more advanced Old World monkeys, or Cer- and myoglobin, indicates that the chimpanzee is our
copithecoidea (Fig. 17-7), are widely distributed in closest relative. There is a 98.4% correlation in DNA
tropical regions of Africa and Asia. They include the sequences between chimpanzees and humans.
familiar macaque, or rhesus monkey of laboratories
and zoos; the Barbary ape of Gibraltar; langurs; The Hylobatidae, such as the gibbons, are the more
baboons; and mandrills. In this group of monkeys, primitive branch of the tail-less apes. Orangutans,
the nostrils are close together and directed downward chimpanzees, and gorillas are grouped within the Pon-
(as in humans), and the tail is not prehensile. gidae. Gorillas are essentially ground dwellers and
spend only a small fraction of their time in the trees.
Anthropoid apes (Fig. 17-8) are tail-less primates.
Modern species evolved from the same ancestral stock cPRIMATE BEGINNINGS
that produced humans. DNA evidence indicates the The early fossil record for primates includes a creature
divergence probably took place between about 7 and named Purgatorius known from only a few teeth dis-
5 million years ago. In this regard, comparative analysis covered in the Late Cretaceous Hell Creek Formation
of the DNA of humans, chimpanzees, gorillas, and other at Purgatory Hill in Montana. Thus, the earliest
apes, as well as similarities in the proteins hemoglobin

548 c Chapter 17. Human Origins

B
A

CD

FIGURE 17-7 Cercopithecoidea (Old World monkeys) include the (A) macaque,
(B) Barbary ape, (C) langur, and (D) baboon. ((A) Richard T. Nowitz/Photo Researchers, Inc.,
(B) Tom McHugh/Photo Researchers, Inc., (C) Tony Camacho/Photo Researchers, Inc., (D) Len
Rue, Jr./Photo Researchers, Inc.)

primates were contemporaries of the last dinosaurs. leading to higher primates can be recognized, includ-
Purgatorius (Fig. 17-9) can be considered a “pre- ing the following:
prosimian” primate. It is placed in a subdivision of
the Order Primates called the Plesiadapiformes. Reduction in muzzle length
Increase in brain size
Plesiadapis (Fig. 17-10), found in Paleocene beds in Shifting of eye orbits to a more forward position
the United States and Europe, is another “pre- Development of a grasping big toe and thumb
prosimian” primate. Its incisors were rodentlike and Development of nails rather than claws
separated from the cheek teeth by a toothless gap
(diastema). Fingers and toes terminated in claws rather These trends are evident in the fossil remains of
than nails. The rodentlike characteristics of Plesiadapis prosimiians like Notharctus and Darwinius. Notharctus
indicate it was a distinctive and specialized primate (Fig. 17-11) lived in tropical rainforests that covered
that was a sterile offshoot of the primate family tree. large regions of North America and Europe during the
early Eocene. Unlike the earlier plesiadapiformes,
The fossil record for primates improves in the early
epochs of the Cenozoic. Several important trends

Primate Beginnings b 549
AB

CD

FIGURE 17-8 Anthropoid apes. (A) The “agile gibbon” is native to Borneo. (B) Orangutan.
These exceptionally long-armed apes seldom leave the protection of forests. They are found
only in Sumatra and Borneo. (C) Male silverback gorilla. Gorillas inhabit tropical forests in
western Africa. (D) Chimpanzees live in groups and have complex social behavior. ((A) David
Maitland/Getty Images, Inc., (B) Tom McHugh/Photo Researchers, Inc., (C) Andrew Dernie/
Getty Images, Inc., (D) Photodisc/Getty Images, Inc.)

FIGURE 17-9 The very primitive Early Paleocene FIGURE 17-10 Paleocene prosimian Plesiadapis. What
primate Purgatorius. The animal was about the size of a features of its skull are rodentlike?
small rat, and probably fed on insects and occasional plant
matter. (Peter Schouten)

550 c Chapter 17. Human Origins

FIGURE 17-11 Eocene
prosimian Notharctus.
(Carlyn Iverson)

Notharctus had flat nails to protect its sensitive finger- tissue, hair, and even the contents of the digestive tract.
tips, and opposable thumbs and great toes. Fruits, nuts, and leaves comprised the little animal’s
last meal. Darwinius had a short face, forwardly
Darwinius masillae (Fig. 17-12) is presently known directed eyes protected by a circle of bone, nails
only by a single specimen found by an amateur fossil instead of claws, and opposable big toes and thumbs.
collector in 1983. It was not scientifically described Absent were characters that would indicate a relation-
until 2009. The fossil was discovered in Germany, in ship to lemurs, such as a grooming claw on the second
the famous Messel fossil site southwest of Frankfurt. It digit of its hind feet, or fused teeth in the middle of its
lived 47 million years ago. The fossil exhibits extra- lower jaws (known as toothcombs). The talus bone
ordinary preservation. Except for a missing left rear that connects the leg and the foot was similar to that
leg, the skeleton is complete. Fine shale in which the seen in humans. These traits in Darwinius appear to
fossil is preserved clearly shows the imprint of soft foreshadow evolution in an anthropoid direction.

Prosimian populations during the Late Paleocene
and Eocene included a variety of tarsiers and lemurs.
Both groups were abundant and widely dispersed on
Northern Hemisphere continents during the Eocene.
However, with the advent of cooler Oligocene climates,
they virtually deserted North America. In the Eastern
Hemisphere they were forced southward into the
warmer latitudes of Asia, Africa, and the East Indies.
Surviving prosimians are much reduced in variety and
number. They probably did not do well in competition
with growing numbers and varieties of monkeys.

FIGURE 17-12 Darwinius masillae, a splendidly cTHE EARLY ANTHROPOIDS
preserved fossil of an early primate from the Messel Anthropoids (the higher primates: monkeys and apes)
Pit fossil site in Germany. (Stan Honda/AFP/Getty were the next evolutionary step. Discoveries in the
Images, Inc.) Fayum region south of the Nile River delta in Egypt
give us a wealth of information about early anthro-
poids. More than a hundred specimens of Fayum
fossils occur in several Oligocene horizons. Many of
the skull fragments and teeth retain subtle vestiges of
prosimian ancestry, but none of the remains are pro-
simians. They are fossils of primates that reached the
monkey stage of organization.
One primate discovered at Fayum is Aegyptopithecus
(Fig. 17-13), a relatively robust arboreal anthropid
with monkeylike limbs and tail, a brain larger than
that of Notharctus, and eye orbits rotated to the front of
the skull. Bone fragments of Aegyptopithecus zeuxis have

The Early Anthropoids b 551

FIGURE 17-13 Aegyptopithecus. This primate,
sometimes called the dawn ape, lived during the
Oligocene around 30 million years ago. Its fossil
remains were discovered in Egypt. Aegyptopithecus
is considered an early ape that preceded the
Miocene apes exemplified by Dryopithecus. (John
Sibbick/The Natural History Museum/The
Image Works)

been dated at 33–34 million years old, indicating that be a very early possible ancestor of Miocene apes. Evi-
the prosimian-anthropoid transition had taken place dence indicates that the transition from prosimians to
by Oligocene time. Egypt was not as arid during the anthropoids, as well as the differentiation of apes from
Oligocene as it is now. It was a well-watered region monkeys, occurred during the Oligocene.
covered with lush tropical forests.
The Miocene was an important epoch in primate
Evolution is a continuing process in which each evolution, and plate tectonics played a role. The unfrag-
animal is a transitional link between older and younger mented block containing Africa and Arabia drifted
species. Thus, it is difficult to assign the fragment of a northward, ultimately colliding with Eurasia. This
fossil jaw or tooth to either the monkey or the ape event blocked east-west circulation of tropical currents
category. One of many clues used to make this assignment across the former Tethys Sea, so East Africa became
isthe teeth—specifically, the cusp patternonmolar teeth. dryer. The dense forests waned, replaced by extensive
In Old World monkeys, certain molars have four cusps. grass-covered plains. These environmental changes
Among apes and humans, these same molars have five created selective pressures that stimulated adaptive
cusps, with an intervening Y-shaped trough. Aegypto- radiation of Old World primates. During the Late
pithecus molars display the Y-5 pattern (Fig. 17-14), which Miocene, primates appeared that gave rise to the pong-
is one reason why anthropologists consider the genus to ids (chimpanzee, gorilla, and orangutan family) on the
one hand, and the hominins on the other.
FIGURE 17-14 General pattern of cusps on the molars of
Old World monkeys. (A) Baboon lower molar showing a New players during the Miocene included:
cusp at each corner. (B) Chimpanzee lower molar showing
the “lazy Y-5” pattern characterized by a Y-shaped Dryomorphs are named from Dryopithecus fon-
depression that separates five cusps. tani, a species first discovered in France in 1856.
Variable in size and appearance, they include
forms from France, Spain, Greece, Hungary,
Turkey, India, Pakistan, and Africa. Many
anthropologists consider the important species
Proconsul africanus to be either a very early dry-
omorph or the immediate dryomorph ancestor.

Proconsul africanus, discovered by Mary and Louis
Leakey in 1948 at Lake Victoria, Kenya, has an
apelike skull, jaws, and teeth (Fig. 17-15). How-
ever, it also has a monkeylike long trunk, arms,
and finger bones. Much like modern monkeys,
Proconsul probably scampered about on all four
legs and lived on fruit.

By about 18 million years ago, after Africa converged
on Eurasia, monkeys and apes migrated into Eurasia.

552 c Chapter 17. Human Origins

FIGURE 17-15 Skull of Proconsul (a dryomorph) from
Lake Victoria, Kenya.

The Miocene apes Ramapithecus, Sivapithecus, and FIGURE 17-16 Australopithecus africanus from South
Gigantipithecus established themselves. Loosely termed Africa. Australopithecus was a bipedal hominin that lived
ramamorphs, these primates are considered the between about 3.5 and 2 million years ago. The creature’s
ancestral stock for both later apes and hominins. dentition indicate an omnivorous diet. Note the heavy brow
Siva-pithecus resembled and is related to modern ridges (supraorbital ridges) and forward-jutting jaws (the
orangutans. It had heavy jaws and robust teeth with prognathus condition). (Pascal Goetgheluck/Photo
molars displaying the Y-5 pattern. Researchers, Inc.)

Miocene primates lack an orderly sequential change The fossil record for primates that can be consid-
along a single trend. The primate family tree is a com- ered possible hominins begins with the discovery of
plex of parallel and diverging branches. It is more of a Sahelanthropus tchadensis, from the central African
family bush than a family tree. Tracing the ascent of nation of Chad, just west of Sudan (Fig. 17-18).
humans through the many splits and dead ends is This upright, 4-foot-tall creature lived 7 to 6 million
difficult. Paleontologists must reinterpret the story years ago. The fossils include a cranium that exhibits a
each time new fossil material is uncovered. mixture of ape and hominin features. Unfortunately,
no vertebrae or limb bones were found, so it is not
cTHE AUSTRALOPITHECINE STAGE possible to prove the animal was fully bipedal. Another
AND THE EMERGENCE OF HOMININS possible early hominin bears the name Orrorin tuge-
nensis. It was discovered in Tugen Hill, Kenya, and
The story of identifying human (hominin) emergence lived about 6 million years ago. Unlike the Sahelan-
begins in 1924. Anthropologist Raymond Dart (1893– thropus tchadensis discovery, the fossils of Orrorin tuge-
1988) discovered fossil remains of an immature pri- nensis include a humanlike upper leg bone (femur).
mate in a South African limestone quarry. He named Thus, this primate was more assuredly a fully bipedal
the fossil Australopithecus africanus (Fig. 17-16). In hominin. Prior to the discovery of Sahelanthropus
succeeding years, others found many additional Aus- tchadensis and Orrorin tugenensis, the oldest known
tralopithecus skeletal fragments. East African fossil sites hominins were the 5.8 to 4.4-million-year-old-species
have yielded hundreds of hominid bones. These fossils of Ardipithecus. Ardipithecus evolved only a few million
provide an unsurpassed record of human evolution years after the hominid branch that led to chimpan-
over the past 4 million years. Some of the eastern zees. It possessed skeletal traits indicating it was adept
African sites, such as Olduvai Gorge (Fig. 17-17), at both upright walking and climbing in trees.
are famous as a result of lifelong research programs
of the Leakeys. Each new field season brings discoveries of homi-
nins younger than Ardipithecus. These discoveries have
Volcanic eruptions were frequent along the eastern provided new information about the complex phylo-
margin of Africa during the Cenozoic, and many of the genetic “bush” of hominin evolution. Among recent
fossil sites have interspersed layers of volcanic ash and finds are more than 20 specimens of Australopithecus
lava flows. This has greatly helped paleoanthropolo- anamensis from Kenya’s Lake Turkana region.
gists, for ash can be dated by the potassium-argon Australopithecus anamensis lived from about 4.2 to
method. Dates from two succeeding ash beds provide a 3.9 million years ago, and thus existed more recently
close age estimate for intervening fossil-bearing sedi- than Ardipithecus ramidus. The species appears to show
ment layers.

The Australopithecine Stage and the Emergence of Hominins b 553

FIGURE 17-17 Rich hominin fossil sites in East Africa. Beds of volcanic ash between fossil
beds facilitate radioisotope dating in this region, and dry conditions limit the amount of
vegetation covering bone beds.

intermediate evolution between Ardipithecus ramidus section of sediments and volcanic ash beds span
and Australopithecus afarensis, the famous “Lucy.” 2.2 million years.

“Lucy” (Australopithecus afarensis) Altogether, the Omo, Koobi Fora, Olduvai, Hadar,
and Laetoli localities have given us sufficient skulls,
“Lucy” (Fig. 17-19) was discovered by Donald Johan- jaws, teeth, and other bones to demonstrate that
son and nicknamed after the Beatles song, “Lucy in the australopithecines were not entirely homogeneous.
Sky with Diamonds.” Her scientific name is Australo- However, certain shared characteristics appear in
pithecus afarensis. Lucy’s pelvic, leg, and foot bones tell nearly all specimens. From the structure of their pelvic
us that she definitely walked erect. Further evidence of girdles, we know that they stood upright in a way more
this came with the discovery of footprints of A. afar- humanlike than apelike.
enensis at Laetoli (Fig. 17-20). We can trace these foot-
prints over 9 meters (30 feet), and they were made by Australopithecine dentition was essentially human,
two contemporaries of Lucy who walked side by side although the teeth were more robust than in modern
over a layer of soft volcanic ash. (Subsequently, another humans. In contrast to these humanlike character-
ashfall formed a protective seal over the footprints.) istics, the australopithecine cranial capacity of about
600 cubic cm was far less than the 1400–1600 cubic cm
Recent excavations for A. afarensis have yielded the in modern humans.
skeletal remains of a male. Named Kadanuumuu
(the Afar language for “big man”) this fellow was about In the past, paleoanthropologists distinguished two
5.5 feet tall and would have towered over the 3.5-foot- kinds of australopithecines:
tall Lucy.
“Gracile” (“gracefully slender”) australopithe-
Rich African Fossil Sites cines had lighter, smaller teeth and somewhat
smaller body size. Lucy is an example.
Eastern African fossil sites have provided an extraor-
dinary number of australopithecine specimens, as “Robust” australopithecines were heavier, and
well as a few teeth and bones of our own species, had massive jaws and teeth. when necessary,
Homo. Such sites include Koobi Fora and Omo (loca- those big teeth were effective in chewing
tion map, Fig. 17-17; Koobi Fora, Fig. 17-21). The coarse nuts and seeds. However, wear patterns
Omo digs are located along the Omo River in remote on the teeth of some do not reveal the pits and
southwestern Ethiopia. Here, a nearly continuous scratches of abrasive foods, indicating a prefer-
ence for munching fruits and softer foods when
they were available. Species include Paranthropus
boisei and Australopithecus robustus. Both appear to

554 c Chapter 17. Human Origins

Modern Homo
Homo erectus
Paranthropus robustus
Paranthropus boisei
Homo rudolfensis
Homo ergaster
Paranthropus aethiopithecus
Australopithecus garhi
Australopithecus africanus

Australopithecus afarensis
Australopithecus anamensis
Orrorin tugenesis
Ardipithicus ramidus
Sahelanthropus tchadensis

76543210
Millions of Years Ago

FIGURE 17-18 Timelines for Pliocene and Pleistocene hominins. The earliest
hominin on the chart is Sahelanthropus tchadensis, discovered in 2002 in the African nation
of Chad, for which it is named.

be evolutionary side branches that went hand and a less flared pelvis more characteristic of
nowhere. early members of the genus Homo. Paleoanthropolo-
gist Lee Berger, whose young son found the first bones
cA SPECIES IN TRANSITION: of A. sediba while accompanying his dad on a fossil-
AUSTRALOPITHECUS SEDIBA hunting trip, regards the discovery as providing “the
ultimate look at a species in transition.”
In April of 2010, new australopithecine fossils were
described from a locality only 25 miles from Johan- Genus Homo
nesburg, South Africa. Named Australopithecus sediba
(Fig. 17-22), the discovery included skeletal remains of Interestingly, the transition from gracile australo-
a young male and adult female. The bones revealed a pithecines to hominins of the genus Homo is not
primate having traits intermediate between australo- marked by striking anatomical differences. Compared
pithecines and our own genus Homo. Headlines to australopithecines, early Homo species had a higher
reported the new species as “part ape and part human.” cranial vault and a somewhat larger cranial capacity.
This was true, for A. sediba had the small brain size, The opening at the base of the cranium, through which
shoulder bones, and long arms of an australopithecine, the spinal cord joins the brain (the foramen magnum),
but at the same time possessed a remarkably modern moved slightly forward, indicating more erect posture.

A Species in Transition: Australopithecus Sediba b 555

FIGURE 17-19 “Lucy,” formally named Australopithecus afarensis. Lucy was a young, erect-walking hominin who lived in East
Africa about 3.5 million years ago. In (A), bones placed at their appropriate locations in the original discovery. Although many
bones are missing, this represents the most complete skeleton of A. afarensis known. (B) is a fleshed-out reconstruction of Lucy.
((A) # The Natural History Museum, London/The Image Works, (B) Gianni Dagli Orti/The Art Archive at Art Resource)

FIGURE 17-20 “Footprints in the ashes of time,” evidence for bipedalism. (A) Footprints probably made by
Australopithecus afarensis about 3.5 million years ago as a pair of these hominins walked across wet volcanic ash. The footprints
document the ability of hominins to walk on two legs. The tracks were discovered in 1976 by Mary Leakey. (B) A female and
male stroll the Late Pliocene landscape of eastern Africa, leaving telltale footprints in the ash, much as vacationers leave
footprints on a wet beach. ((A) John Reader/Science Photo Library/Photo Researchers, Inc., (B) American Museum of Natural
History Library)

556 c Chapter 17. Human Origins

FIGURE 17-21 Paleoanthropologists Meave
Leakey (wife of Richard Leakey) and her
daughter Louise Leakey applying a protective
covering to a fossil discovered at the Koobi Fora
site in eastern Africa. Both Australopithecine
remains and the skull of an early member of the
genus Homo were discovered at Koobi Fora. Other
discoveries include stone choppers and flake tools
found in association with hippopotamus bones.
Finding tools and bones together suggest that this
was a butchering site. We infer that about
1.8 million years ago, some australopithecines came
across a recently deceased hippopotamus and used
the sharp edges of flaked chert to get at the meat.
(NG Image Collection)

Premolars were narrower, with a shorter row of cheek cooler and drier. As a result, rainforests gave way to
teeth. Notably, crude stone tools are found in associa- broad expanses of grasslands. In this more open and
tion with Homo fossils. difficult environment, hominins would have experi-
enced selective pressures that could have led to
The oldest Homo remains are nearly 2.5 million improved bipedalism, greater intelligence, and the
years old. Jaw fragments and teeth occur near stone development of a stone tool technology.
tools of the same age. By about 2 million years ago,
Homo rudolfensis (Fig. 17-23) and Homo ergaster (also cTHE HOMO ERECTUS STAGE
called Homo habilis) were roaming the African plains. The next stage in hominid evolution is represented by
Homo erectus (Fig. 17-24). This is the first hominin
What conditions triggered the evolution of Homo
from Australopithecus? We now have ample evidence
that about 2.7 million years ago, Africa began to grow

FIGURE 17-22 Reconstruction of the head of FIGURE 17-23 By about 2 million years ago, Homo
Australopithecus sediba. This hominin lived in South Africa rudolfensis roamed the African plains. The hominin lived
about 2 million years ago. Anthropogists are currently in eastern Africa from about 1.9 to 1.8 million years ago. The
considering whether A. sebida is an early species of Homo or a Koobi Fora fossil site provided this specimen. (# The
late-surviving member of Australopithecus Africans. (Mauricio Natural History Museum, London/The Image Works)
Anton/Photo Researchers, Inc.)

FIGURE 17-24 Reconstruction of a female Homo erectus Final Stages of Human Evolution b 557
based on the remains of many individuals discovered in
China. (# The Natural History Museum, London/The skeleton reveals a long-limbed, tall, slender individual.
Image Works) Adults would be about the same size or larger than
many natives of eastern Africa today. Below the neck,
known to have moved out of Africa into Eurasia. the Turkana boy had a remarkably modern skeleton.
Noteworthy discoveries include:
Although the post cranial skeleton of Homo erectus
A lower jaw with teeth from the Caucasus Moun- was generally similar to that of modern humans, the
tains (1.8 million years old) skull was not. Cranial capacity ranged from about 775
cubic cm to nearly 1300. In comparison, brain capacity
A largely complete skeleton from the western in modern Homo sapiens is 1400–1600 cubic cm. Thus,
Turkana fossil site (1.5 million years old) the maximum brain size of Homo erectus approaches near
the bottom range of modern people. Most would agree
A skull cap from Bed II of Olduvai Gorge that Homo erectus represents a stage in hominin evolu-
(750,000 years old) (Fig. 17-25) tion during which relatively rapid increase in brain size
had begun. No doubt the expansion of the brain
The Turkana skeleton is that of a boy, aged 11–13, involved the reshaping of both the cranium and the
who perished in a marsh and was quickly covered with birth canal to accommodate fetuses with larger heads.
mud so his body was not shredded by scavengers. The
Aside from its larger cranial capacity, the Homo
erectus skull was massive and rather flat. Above the eyes
were heavy, bony, supraorbital ridges (see Fig. 17-23).
The forehead sloped, and the jaw jutted forward at the
tooth line (a condition termed prognathous). A jut-
ting chin was lacking, and the nose was broad and flat.
These were rather primitive traits. However, the teeth
and dental arcade in Homo erectus were essentially
modern, although somewhat more robust.

There is ample evidence that Homo erectus made good
use of his larger brain. From the bones of other animals
found where they lived, it is clear these hominins were
excellent hunters. They also were skilled at making
simple implements of flint and chert (Fig. 17-26), such
as axes and scrapers. Some also appear to have engaged in
cannibalism, either for food or as a part of a ritual.

Paleontologists do not know if Homo erectus spoke a
distinctive language, wore clothes, or built dwellings.
There is vague evidence that they hunted together in
bands. What appear to be slaughter sites have been
found in Europe. Unfortunately, these sites did not
yield any bones of Homo erectus to confirm they were
the people doing the slaughtering. A few fossil locali-
ties in Europe and China contain traces of carbon,
suggesting that Homo erectus had learned to use fire
(Fig. 17-27).

Homo erectus fossils of differing ages and locations
show some variability. Some paleoanthropologists
consider this reason enough to divide Homo erectus
into two or more species, whereas others consider the
variability no greater than what we see today among
our own species.

cFINAL STAGES OF HUMAN
EVOLUTION

FIGURE 17-25 Homo erectus cranium found at Olduvai The Neandertals
Gorge, Tanzania, by Louis Leakey in 1960. The specimen
was found associated with stone implements. (# The From the Homo erectus stage of the Middle Pleistocene,
Natural History Museum, London/The Image Works) it is a short step to Late Pleistocene hominins called
Neandertals (Fig. 17-28). Some paleoanthropologists

558 c Chapter 17. Human Origins

ENRICHMENT

Being Upright: Good News, Bad News In addition, evolutionary changes associated with our
upright stance have increased the distance between the low-
We are unique among primates in several ways. One is by est ribs and the top of the pelvis. This gives us our distinctive
having a body structured for standing and walking fully erect waist, but also weakens the abdominal wall. Thus, we are
on our two legs. Our nonhuman ancestors walked on all fours, particularly prone to hernias (ruptures).
or like apes, used their forelimbs as well as hindlimbs in walk-
ing and running. Apes and monkeys also differ from hom- But for survival, the advantages of erect posture far
inins in having a grasping foot with curved toe bones and outweigh the disadvantages. An upright stance and biped-
opposable big toe. The evolutionary transition from these not alism freed our hands for the precise manipulation that led to
fully erect apes to the fully bipedal hominin condition had its tool manufacture and the advent of technology. For humans,
challenges. hands are not merely motor organs. They also are sensory
organs that can investigate by touch, “seeing” into places
For example, the human vertebral column is somewhat the eye may not reach. Our hands explore and react to what
imperfect as a vertical support. That imperfection is has been discovered. They can gesture, give instruction,
one reason why so many people are plagued by lower indicate directions, and even express emotion.
back pain. Under the weight of the upper body, and pro-
voked by lifting and unusual movements, intervertebral If we merely walked on our hands, what chance would we
discs may become herniated and protrude, causing pres- have had to evolve the complex human brain that provides for
sure against nerve structures. Severe pain and disability abstract thought, symbolic communication, and the devel-
may follow, the treatment for which often requires delicate opment of culture?
neurosurgery.

regard Neandertals as a variety or subspecies of Homo calories a day to support his body mass in the cold
sapiens, which they have designated Homo sapiens climate. In contrast, modern humans get on well with
neandertalensis. half that daily calorie intake.

Radiocarbon dating of a jawbone from Croatia Many Neandertals lived in caves (Fig. 17-31) and
indicates that Neandertals were in central Europe as hunted large animals for food. They hunted mam-
recently as 28,000 years ago (Figure 17-29). This moth, woolly rhinoceroses, reindeer, bison, and fierce
means that Neandertals and early modern humans ancestors of modern cattle known as aurochs. In order
coexisted for thousands of years. to kill and butcher the game they killed, Neandertals
made a variety of stone spear points, scrapers, borers,
The first Neandertal specimen was found in Ger- knives, and saw-edged tools. They made ample use of
many, in the Neander River Valley, giving the species fire, and could ignite one at will in the hearths they
its name. Subsequently, many additional fossils have excavated in the floors of caves. Thus far, evidence is
been found, indicating that Neandertal people ranged lacking that Neandertals gathered seeds and nuts to
across the entire Old World for a period of about supplement their diet.
200,000 years. With their heavy brow ridges and
prognathous (jaws projecting forward from the face), The technology of fire use and control had obvious
chinless jaws, Neandertals have become the stereotyp- advantages for Pleistocene hominins. It provided light
ical “cave man.” Indeed, their face seems a brutish in caves, gave warmth, and protection from predators.
carryover from the Middle Pleistocene. During frigid Ice Age winters, fire thawed meat that
froze quickly after a kill. Cooking may have been a
Below the neck, Neandertal skeletons were some- simultaneous discovery with the thawing process.
what more robust than our own. They were rather Cooking foods promoted easier digestion and destroyed
bulky around the middle because of a more flared rib harmful microorganisms.
cage and pelvis (Fig. 17-30). Their brain size equaled
or even exceeded that of present humans. Thus, the In addition to fire, Neandertals constructed shel-
once popular depiction of Neandertals as bent-kneed, ters of skins, sticks, and bones where there were no
flatfooted, bullnecked brutes with curved backs is caves. We think that they also cared for their sick,
incorrect. In fact, much of that early interpretation pondered the nature of death, and believed in an
was from restoration of an elderly Neandertal skeleton afterlife, based on their custom of burying artifacts
that had severe osteoarthritis. with the dead.

Most “classic Neandertals” were muscular, sturdy This is not to say that Neandertals were a kind and
people. They apparently adapted well to chilly living gentle folk. A cave in southwestern France contained
near the edge of glacial ice sheets. Relatively short the bones of at least six Neandertals that clearly had
limbs and a bulky torso may have helped conserve been deliberately butchered. Was cannibalism wide-
body heat. Even with this advantage, however, a typical spread among Neandertals? If so, was it a dietary habit
Neandertal male would have needed up to 5,000 or did it occur only during famine? We don’t know.

Final Stages of Human Evolution b 559

FIGURE 17-26 Progressive improvement in tool-making from stone during the
Pleistocene. The crude stone tools of the Early Pleistocene (bottom) were produced by
australopithecines. Homo erectus produced the better-shaped tools of the Middle Pleistocene.
The Upper Paleolithic tools included carefully chipped blades and points. The next stage, not
shown here, is the Neolithic, with refined and polished tools of many kinds.

ENRICHMENT

Neandertal or Neanderthal? What is the reason for the difference in spelling? Early in
the twentieth century, the government of Germany decided
You may have noticed that this text uses the spelling Nean- to change the spelling of German words to make them
dertal, whereas the alternate spelling Neanderthal, with an consistent with the way they are pronounced. There is no
“h” after the “t,” is prevalent in many publications. Here, we “th” (as in though) sound in German, so that “thal” became
follow the spelling used by Erik Trinkhaus and Pat Shipman “tal.” The location formerly called Neander Thal, now
in their excellent book, The Neandertals. became Neander Tal.

Be assured that both spellings for this remarkable group Of course, the spelling of the original taxonomic name
of prehistoric hominids are correct. The name is derived from neanderthalensis could not be changed. International rules
a location in Germany where Neandertal fossils were found for zoological nomenclature mandate that the first valid
by quarry workers in 1856. In German, it is known as the name applied to an animal must be retained.
Neander Thal, which translates as the Neander Valley. The
famous fossil was quickly dubbed Neanderthal man.

560 c Chapter 17. Human Origins

ENRICHMENT

Neandertal Ritual protect the body, or possibly to restrain the deceased from
returning to life.
The Neandertals lived from about 125,000 to about
28,000 years ago. Their culture included chipped flint That Neandertals had a special attitude about death also
tools, crude carvings, the use of fire, and burial of their is evident at a fossil site in Uzbekistan, near Russia. Anthro-
dead in carefully prepared graves. Some burial sites contain pologists working there uncovered an array of goat horns
indications of religious beliefs. For example, consider the surrounding the buried body of a 9-year-old child.
La Chapelle fossil site in southwestern France. It contains a
Neandertal male, placed in ritual position within a shallow Yet another interesting Neandertal fossil site is in Sha-
grave, with a bison leg on his chest. Flint tools also are in the nidar, Iraq. Researchers uncovered the remains of nine
grave, possibly in the belief that they could be used in an Neandertals, four of whom were deliberately buried. One
afterlife. burial contains assorted pollen grains, suggesting that flow-
ers may have been placed in the grave.
At the Ferrassie Neandertal site in France, an apparent
family cemetery was discovered within a rock shelter. Two Although not related to funerary ritual, the Shanidar site
adults, presumed to be a father and mother, are buried head also includes the remains of a 30-year-old male who had
to head. Nearby, three small children and a newborn infant been born with a crippled arm. The arm was amputated
are buried. Once again, flint flakes and bone splinters were below the elbow, and this hardy Neandertal survived the
placed in the grave of the adult male. A heavy, flat stone was surgery. The excessive wear on his teeth suggests that he
placed over his head and shoulders. Perhaps the stone was to used them to compensate for his missing limb.

Could Neandertals talk with one another? Recent species. Digging in a cave on the Indonesian island
studies of DNA extracted from Neandertal bones of Flores, they hoped to find evidence of Homo erectus.
contain a gene believed to be essential for the devel- Instead, they unearthed stone tools and bones of a new
opment of language. This “speech gene” governs the species, Homo floresiensis (Fig. 17-32).
control of muscles involved in forming words with lip,
larynx, and tongue. The site produced bones of seven small individuals,
including the complete skeleton of an adult female.
Little People of the South Pacific Adults were only three feet tall, prompting the popular
press to call them “hobbits of the South Pacific,” after
In 2004, a team of Australian and Indonesian scientists the short people in J.R.R. Tolkien’s Lord of the Rings.
announced a remarkable discovery: a new human
Although the ancestry of H. floresiensis is uncertain,
anthropologists working at the site believe that Homo

FIGURE 17-27 A group of Homo erectus people
using fire to make tools while others return
from hunting. (Photo Researchers, Inc.)

FIGURE 17-28 Skull of a Classic Neandertal. From the Final Stages of Human Evolution b 561
Homo erectus stage of the Middle Pleistocene.
Neandertals. They quickly were assimilated or
erectus reached Flores by about 800,000 years ago, and replaced the Neandertals through tribal warfare and
may have evolved into the smaller species as a result competition for hunting grounds.
of living on an island with few large predators and
limited food. These early members of our own species are gene-
rally called Cro-Magnon (Figs. 17-33 and 17-34). They
Homo floresiensis lived as recently as 13,000 years are also called “early modern humans.” They were
ago, and was a contemporary of Neandertals and mostly taller than Neandertals, had a more vertical
modern humans. They were a clever people who brow, and had a decided chin projection (Fig. 17-35C).
knew how to hunt, use fire, and make carefully crafted In short, Cro-Magnon’s bones were modern, and anthro-
points, blades, and awls from stone. pologists have recognized definite Cro-Magnon skull
types among today’s western and northern Europeans.
Not all paleontologists agree that the Flores fossils
represent a new species. Some believe they are a dwarf Cro-Magnon continued and further developed the
or pygmy variety of Homo sapiens. cultural traditions of the Neandertals. Finely crafted
spear points, awls, needles, scrapers, and other tools
are found in Cro-Magnon caves. Handsome paintings
and drawings were made on cave walls and ceilings.
Engravings and sculptures include mammoths, horses,
and women (Fig. 17-36). These were produced from
fragments of bone or ivory. The statues of women
probably were used in fertility rites.

Evidence is that Cro-Magnon people enjoyed wear-
ing body ornaments and frequently fashioned neckla-
ces from pieces of ivory, shells, and teeth. Burial of the
dead became an elaborate affair. Hunters were buried
with their weapons and children with their ornaments.
This apparent concern for an afterlife and the sense of
self-awareness that resulted in art and complex ritual
suggest that the beginning of the age of the philoso-
pher had arrived.

Cro-Magnon People Beginnings of Recorded History
About 34,000 years ago, during the fourth glacial
stage, humans closely resembling modern Europeans Through most of the species’ early history, Homo sapiens
moved from Africa into regions inhabited by the was a wandering hunter and gatherer of wild edible
plants. However, about 15,000 to 10,000 years ago, near
FIGURE 17-29 As indicated by the radiocarbon date the beginning of the Holocene Epoch, tribes began to
obtained from this Neandertal jawbone, Neandertals domesticate animals and cultivate plants. They learned
roamed central Europe as recently as 28,000 years ago. to grind their tools to unprecedented perfection and to
The date also indicates that Neandertals and early modern make utensils of fired clay. With more reliable sources
humans coexisted for thousands of years. There is evidence of food, permanent settlements developed. Individuals
of interbreeding. (# AP/Wide World Photos) were spared the continuous demand of searching for
food, and so were able to build and improve their
cultures. Languages improved, and symbols developed
into forms of writing. With writing came the beginning
of recorded history.

Not immediately, but in only a fraction of geologic
time, humans became agents of geologic change. For
many thousands of years, their influence on the planet
was minimal, but this changed with the beginning of
the Industrial Revolution in the early nineteenth cen-
tury. Changes in the composition of the atmosphere
with related modifications in global temperature and
composition of the ocean are having far-reaching
consequences for life. Recognition of the way human
activities are altering the Earth has prompted geolo-
gists to consider designating a new geologic time term
for the age we live in. If adopted, it will be called the

562 c Chapter 17. Human Origins

FIGURE 17-30 Neandertal skeleton (A)
compared with the skeleton of a
modern human (B). The Neandertal
skeleton is more robust and has a more
flaring rib cage. This provided more space
for larger lungs, needed for a higher level
A B of activity. (EPA/NewsCom)

FIGURE 17-31 Reconstruction of a Neandertal
family group. The technology of fire use and
control had obvious advantages for Pleistocene
hominins. (Courtesy of U.S. National Museum of
Natural History, Smithsonian Institution)

Humans Arrive in the Americas b 563

FIGURE 17-32 Homo floresiensis, returning from a FIGURE 17-33 Skull of a Cro-Magnon human. As in
successful hunt. Adult males, such as the one pictured here, present-day humans, the face of Cro-Magnon was vertical
were only about a meter tall. These dwarf humans were rather than prognathus (jaws projecting forward). The heavy
discovered in 2003 in Liang Bua cave on the Indonesian supraorbital ridges of many European Neandertals are not
Island of Flores. (Peter Schouten) present, and there is a prominent chin. (# The Natural
History Museum, London/The Image Works)
Anthropocene. The concept is currently under study
by the Anthropocene Working Group of the Interna- must trace human presence through discarded frag-
tional Commission on Stratigraphy. ments of tools or weapons, rather than actual skeletal
remains. Actual dating can be difficult and flawed by
cHUMANS ARRIVE IN THE AMERICAS contamination. For these reasons, it still is not definitely
The record for hominins in the New World is disconti- known when the first human set foot in America.
nuous and often ambiguous. Too often, anthropologists
A classic hypothesis suggests that bands of humans
entered North America by way of a land bridge
spanning the present trend of the Bering Straits
between Asia and Alaska. During glacial stages, sea
level would have dropped as much as 100 meters,
exposing a rich tract of grazing land hundreds of miles
wide. Migrating herds of reindeer, elk, and bison, as

FIGURE 17-34 Cro-Magnon children
being shown how to make stone tools.
(Christian Jegou/Photo Researchers, Inc.)

564 c Chapter 17. Human Origins

FIGURE 17-35 Skull comparison. (A) Neandertal. (B) Skull from a rock shelter on the slope of Mount Carmel (Israel) that
appears to show both Neandertal and Cro-Magnon features. (C) Cro-Magnon. The Mount Carmel skull is intermediate in
both form and age between Neandertal and Cro-Magnon.

well as mastodons and mammoths, lived along the land Asia lay at the west end of the land bridge, and the
bridge, enticing human hunters from Siberia. Humans first arrivals to America were certainly Asian. Linguis-
entered the New World with much the same motiva- tic studies and mitochondrial DNA clearly link native
tion as other predators. They followed the source of Americans to Asian populations. But precisely when
their sustenance. these migrations occurred is difficult to determine and
hotly debated:
Once they had crossed the land bridge, the migrat-
ing clans were able to follow an ice-free corridor There is unassailable evidence that human popu-
down into Canada, the United States, and even South lations lived in North America about 12,000 years
America. Earlier, the same route had been used by ago. That evidence consists mainly of stone tools
mammoth, reindeer, the dire wolf, bear, and other and weapons made by people of the Clovis
mammals. culture, named for an archeological site in

FIGURE 17-36 Prehistoric art and tool-making by Late Pleistocene Homo sopiens.
(A) Statuette of a female figure known as “The Venus of Willendorf.” The statuette is about
11 cm tall. It was carved from oolitic limestone and stained with an iron-oxide pigment 24,000 to
22,000 years BCE. Many believe carvings like this one served as fertility symbols. (B) Tools made
from bone by Late Pleistocene humans. ((A) Art Resource, (B) Gianni Dagli Orti/The Art
Archive at Art Resource.)

Human Population: 7 Billion and Growing b 565

New Mexico. Clovis artifacts, however, are have been found in kill sites in association with extinct
known throughout the New World from Alaska species of bison.
down into South America.
cHUMAN POPULATION: 7 BILLION
At a site in western Pennsylvania known as the AND GROWING
Meadowcroft Shelter, stone weapon points and
tools have been uncovered that indicate human One of the many lessons of historical geology is that
occupation since about 19,600 years ago. How- the arrival of Homo sapiens is only one very recent and
ever, there is concern that the radiocarbon used in momentary event along the 500-million-year evolu-
dating materials at the site might have been tion of vertebrates. Yet even though Homo sapiens
contaminated by nearby coal deposits. arived recently, we humans are now the most abun-
dant vertebrate species on Earth. We have also had a
There are several South American contenders for far greater impact on the planet’s environment than
pre-Clovis humans in America, some yielding any other group of vertebrates. As indicated in
dates as old as 13,000 years. Figure 17-37, world population reached 7.0 billion
in the year 2010. It is expected to reach 9 billion
Numerous more recent sites yield indirect evidence by 2050.
of paleoindians. In the western United States, projec-
tile points are found in definite association with extinct Can Earth sustain such an exploding human popu-
Late Pleistocene elephants and bison. Sites near Clovis lation? Resources are limited, and environments are
and Sandia, New Mexico, have yielded spear points easily damaged.
and tools of two separate cultures that existed from
about 13,000 to 11,000 years ago. A somewhat more Already, we have squandered about a fifth of the
recent group of paleoindians lived from about 11,000 topsoil needed to grow food.
to 9000 years ago, called the Folsom Culture. Folsom
people manufactured short, finely flaked projectile Over the past five decades we have lost a third of
points that were mounted on shafts. These flints the globe’s forested areas.

FIGURE 17-37 World population growth. (After United States Dept. of State Information
Circular)

566 c Chapter 17. Human Origins geologic time. On a grander time scale, the Milanko-
vitch cycles will probably operate in bringing alter-
About an eighth of all agricultural land has been nating episodes of glaciation and interglacial warmer
altered to barren desert, partly as a result of stages.
overgrazing associated with the demand for meat.
In the more distant future, Earth will continue to
Some soil productivity has been lost due to accu- undergo changes in its interacting systems. Plate tec-
mulation of mineral salts caused by extensive tonics, for example, will continue to operate in future
irrigation. yet unnamed epochs, just as it has in the past. If
present-day plate movements continue, the Atlantic
Water shortages now are critical in many regions. will continue to widen. In about 50 million years, the
Mediterranean will close as Africa converges on
Climate-altering greenhouse gases have incre- Europe. The collision will produce a mountain range
ased by more than a third, with a 5% reduction extending across what was once the Mediterranean to
of the ozone layer that protects all life from lethal the Persian Gulf. Australia will collide with Southeast
ultraviolet radiation. Asia. Baja California will slide northward to Alaska.
Eventually another supercontinent will be assembled.
Global warming resulting from atmospheric pol- Like its predecessors Rodinia and Pangea, it too will
lution will bring melting of ice caps and conse- eventually fragment. And all of these transformations
quent rise in sea level, water shortages and will cause changes in global climates, as major ocean
increased aridity on land, more extreme weather currents are shunted to different locations and land-
worldwide, enhanced spread of tropical deseases masses move to and from polar locations.
northward, famine and flooding in many parts of
the world, and host of related problems. If we could peer yet farther into deep time, we
would see a far less hospitable Earth. We can expect
Our mineral resources are also finite. As they are about a billion more years of warming from the Sun as
consumed and become rare or require more expen- its temperature gradually increases. Eventually, the
sive extraction and refining, costs rise and standards Earth will be too hot to sustain life. In about 7 billion
of living decline in even the richest of nations. years, the Sun will expand into a red giant and will
engulf the orbits of Mercury, Venus, and possibly an
cWHAT LIES AHEAD? already seared and cindered Earth as well.
We are now at the end of our journey through geologic
time. We have surveyed how our planet and its inhab- To end our journey on a more hopeful note, we
itants changed over the past 5.5 billion years. We humans still have hundreds of potential generations of
humans arrived a mere 2 million years ago. Will our descendants that will live on this goldilocks planet. It is
lineage last as long as that of the dinosaurs? They vital that we all work to solve the problem of explosive
survived over 140 million years. However, they did not population growth because it leads inevitably to fouling
have the resource, food, and pollution problems we of our environment, exhaustion of vital resources, and
humans face today. biologic extinctions. The task is vast and complex. If we
As for our planetary home, global climates and sea fail, other animals may replace our species and add their
level will be influenced in the next few centuries by own distinctive chapters to the history of life on Earth.
greenhouse gases released into the atmosphere. But
this will occur over a mere miniscule interval of

SUMMARY

Arboreal prosimians were the dominant primates during less forest area and more prairie. The ramamorphs were
the Paleocene and Eocene. By the Oligocene, monkeys the probable ancestors of both apes and humans.
and apes had appeared.
Australopithecines were fully erect, primarily Pliocene
The general evolutionary changes in apes during the hominids.
Cenozoic included the following:
Loss of the long snout, development of a flatter face, During the middle Pleistocene, Homo erectus began to
reshaping of the head to a more rounded form. populate much of Africa, Asia, and Europe. These
erect-walking hominins had larger brains than the Aus-
Relocation of the eyes to a more forward position for tralopithecines and improved tool-making abilities.
improved binocular vision.
The late Pleistocene was marked by the appearance of
Development of hands capable of grasping and manip- Neandertal peoples.
ulating objects.
Anatomically modern Homo sapiens spread widely during
Skeletal modifications accompanying a trend toward the late Pleistocene. An early group known as Cro-Mag-
erect posture. non replaced the Neandertals.

Apes known as dryomorphs and ramamorphs were com- Humans may have come to the Americas by migrating
mon during the Miocene when climate change resulted in across the Bering land bridge.

Anthropoidea, p. 545 Questions for Review and Discussion b 567
arboreal, p. 544
australopithecine, p. 553 KEY TERMS
brachiating, p. 545
Ceboidea, p. 546 Hylobatidae, p. 547
Cercopithecoidea, p. 547 Neandertals, p. 557
Clovis culture, p. 564 nocturnal, p. 546
Cro-Magnon people, p. 561 paleoindians, p. 565
dryomorphs, p. 551 Pongidae, p. 547
hominins (Homininae), p. 545 prehensile (tail in primates), p. 546
primates, p. 544
prognathous, p. 557
Prosimii, p. 545
ramamorphs, p. 552

QUESTIONS FOR REVIEW AND DISCUSSION

1. In general, how do prosimians differ from anthropoids? 10. Prepare text for a debate in which you first argue for
What kinds of primates are hominoids (members of the and then against the premise that life will be more difficult
Superfamily Hominoidae)? What kinds of primates are for humans during the year 2050 than it is today.
hominids (members of the Family Hominidae)?
11. What conditions near and along the East African Rift
2. Early arboreal primates such as Notharctus had close-set Valley are favorable for the discovery and dating of Late
eyes and grasping hands. Other than facilitating movement Neogene vertebrates?
among tree branches, what function might these attributes
have provided? 12. The Primate Subfamily Homininae includes:
___a. All apes and humans
3. During what geologic period do we find the earliest ___b. Just African apes and humans
known remains of primates? When does the first member of ___c. Members of the genus Homo, as well as extinct
the genus Homo appear? fully bipedal ancestors of Homo, such as Austral-
opithecus, Paranthropus, and Ardipithecus
4. What physical properties of chert and flint render these ___d. Macaques, baboons, and mandrills
rocks useful in the manufacture of spear points, axes, and
scrapers by early humans? 13. Purgatorius Plesiadapis, Darwinius, and Notharctus are:
___a. Extinct anthropoids
5. Why is it easier to find fossils and date them in the ___b. Extinct prosimians
eastern African fossil sites than in many other parts of the ___c. Extinct dryomorphs
world? ___d. Extinct gibbons

6. What distinctly humanlike traits were possessed by 14. In the chronological succession of hominins:
Australopithecus? What apelike characteristics were retained? ___a. Sahelanthropus appeared before Ardipithecus
___b. Ardipithecus appeared before Australopithecus
7. What features of Cro-Magnon people differentiate them ___c. Ardipithecus appeared before Paranthropus
from Neandertal people? ___d. Paranthropus appeared before Homo erectus
___e. All of the above
8. Discuss the general changes in the skulls of fossil pri-
mates as one progresses from an animal such as Plesiadapis to
modern humans.

9. Discuss the route by which Homo sapiens may have
entered the New World. Would the migrations have been
easier during a glacial or interglacial epoch? Why?



A1

A2 c Appendix A

Classification of Living Things b A3

A4 c Appendix A



A6



A8 c Appendix C

A9

A10

A11

A12

GLOSSARY

For terms not included in this glossary, students may wish Alpha particle A particle equivalent to the nucleus of a
to consult the Glossary of Geology (1997, edited by J. A. helium atom, emitted from an atomic nucleus during
Jackson, 4th ed., Falls Church, Virginia, American Geo- radioactive decay.
logical Institute).
Alpine orogeny In general, the sequence of crustal distur-
Absaroka sequence A sequence of Permian–Pennsylvanian bances beginning in the middle Mesozoic and continuing
sediments bounded both above and below by a regional into the Miocene that resulted in the geologic structures
unconformity and recording an episode of marine trans- of the Alps.
gression over an eroded surface, full flood level of inunda-
tion, and regression from the craton. Amino acids Nitrogenous hydrocarbons that serve as the
building blocks of proteins and are thus essential to all
Absolute geologic age The actual age, expressed in years, living things.
of a geologic material or event.
Ammonites Ammonoid cephalopods having more com-
Acadian orogeny An episode of mountain building in the plex sutural patterns than either ceratites or goniatites.
northern Appalachians during the Devonian Period.
Ammonoids An extinct group of cephalopods with coiled,
Acanthodians The earliest known vertebrates (fishes) with chambered conch(s) and having septa with crenulated
a movable, well-developed lower jaw, or mandible; hence, margins.
the first jawed fishes.
Amniotic egg An egg produced by reptiles, birds, and
Accretionary tectonics The growth of continents by monotremes in which the developing embryo is main-
accretion of island arcs, oceanic ridges, and microconti- tained and protected by an elaborate arrangement of shell
nents as they are transported to subduction zones. membranes, yolk, sac, amnion, and allantois.

Accretionary terrane A block of continental crust having Amphibians “Cold-blooded” vertebrates that utilize gills
fault boundaries that is geologically distinct from sur- for respiration in the early life stages but that have air-
rounding terranes. breathing lungs as adults.

Adaptation A modification of an organism that better fits Amphibole A ferromagnesium silicate mineral that occurs
it for existence in its present environment or enables it to commonly in igneous and metamorphic rocks.
live in a somewhat different environment.
Anaerobic organism An organism that does not require
Adaptive radiation The diversity that develops among oxygen for respiration but rather makes use of processes
species as each adapts to a different set of environmental such as fermentation to obtain its energy.
conditions.
Andesite A volcanic rock that in chemical composition is
Adenosine diphosphate (ADP) A product formed in the intermediate between basalt and granite.
hydrolysis of adenosine triphosphate that is accompanied
by release of energy and organic phosphate. Angiosperms An advanced group of plants having floral
reproductive structures and seeds in a closed ovary. The
Adenosine triphosphate (ATP) A compound that occurs “flowering plants.”
in all cells and that serves as a source of energy for
physiologic reactions such as muscle contraction. Anthropoidea The suborder of primates that includes
monkeys, apes, and humans.
Aerobic organism An organism that uses oxygen in car-
rying out respiratory processes. Anticline A geologic structure in which strata are bent into
an upfold or arch.
Age The time represented by the time-stratigraphic unit
called a stage. (Informally, may indicate any time span in Antler orogeny A Late Devonian and Mississippian
geologic history, as “Age of Cycads.”) episode of mountain building involving folding and
thrusting along a belt across Nevada to southwestern
Agnatha The jawless vertebrates, including extinct ostra- Alberta.
coderms and living lampreys and hagfishes.
Aragonite A calcium carbonate mineral (CaCO3) that
Albedo The percentage of incoming solar radiation that is differs from calcite in its crystal form. (Aragonite is
reflected by the ground, ice, snow, water, clouds, or orthorhombic rather than rhombohedral as in calcite.)
particulates in the atmosphere.
Archaea The domain that includes thermophylic (heat-
Algae Any of a large group of simple plants (thallophyta) dependent), halophylic (salt-dependent), methane-pro-
that contain chlorophyll and are capable of ducing, and sulfur-producing bacteria. (The remaining
photosynthesis. two domains are the Bacteria and Eurkarya.)

Allegheny orogeny The late Paleozoic episodes of Archaeocyatha A group of Cambrian marine organisms
mountain building along the present trend of the having double, perforated, calcareous walls and conical-
Appalachian Mountains. (Also termed the Appalachian to-cylindric skeletal form. Archaeocyathids lived during
orogeny.) the Cambrian.

Alleghenian orogenic belt Regional tract of Paleozoic Archean Pertaining to the division of Precambrian time
rocks strongly deformed during the Allegheny orogeny. beginning 3.8 billion years ago and ending 2.5 billion
years ago.
Alluvium Unconsolidated, poorly sorted detrital sedi-
ments ranging from clay to gravel sizes and characteristi- Archosaurs Advanced reptiles of a group called diapsids,
cally fluvial in origin. which includes thecodonts, “dinosaurs,” pterosaurs, and
crocodiles.

G1

G2 c Glossary Bivalvia A class of the Phylum Mollusca (also known as the
Class Pelecypoda).
Arcoids A group of bivalves (pelecypods) exemplified by
species of Arca. Blastoids Sessile (attached) Paleozoic echinoderms
having a stem and an attached cup or calyx composed
Artiodactyl Hoofed mammals that typically have two or of relatively few plates.
four toes on each foot.
Bolide A meteorite, asteroid, or comet that explodes on
Asteroid One of numerous relatively small planetary bod- striking the Earth.
ies (less than 800 kilometers in diameter) revolving around
the Sun in orbits lying between those of Mars and Jupiter. Brachiating Swinging from branch to branch and tree to
tree by using the limbs, as among monkeys.
Asthenosphere The zone between 50 and 250 kilometers
below the surface of the Earth, where shock waves of Brachiopod A bivalved (doubled-shelled) marine inverte-
earthquakes travel at much reduced speeds, perhaps brate. Brachiopods were particularly common and wide-
because of less rigidity. The asthenosphere may be a spread during the Paleozoic and persist in fewer numbers
zone where convective flow of material occurs. today.

Atoll A ring-like island or a series of islands formed by Breccia A clastic sedimentary rock composed largely of
corals and calcareous algae around a central lagoon. angular fragments of granule size or larger.

Atom The smallest divisible unit retaining the character- Bryozoa A phylum of attached and incrusting colonial
istics of a specific element. marine invertebrates.

Atomic fission A nuclear process that occurs when a heavy Burgess Shale fauna A beautifully preserved fossil fauna
nucleus splits into two or more lighter nuclei, simulta- of soft-bodied Cambrian animals discovered in 1910 by
neously liberating a considerable amount of energy. Charles Walcott in Kicking Horse Pass, Alberta, Canada.

Atomic fusion A nuclear process that occurs when two Caledonian orogeny A major early Paleozoic episode of
light nuclei unite to form a heavier one. In the process, a mountain building affecting Europe that created an oro-
large amount of energy is released. genic belt, the Caledonides, extending from Ireland and
Scotland northwestward through Scandinavia.
Atomic mass A quantity essentially equivalent to the
number of neutrons plus the number of protons in an Carbon-14 A radioactive isotope of carbon with an atomic
atomic nucleus. mass of 14. Carbon-14 is frequently used in determining
the age of materials less than about 50,000 years old.
Atomic number The number of protons in the nuclei of
atoms of a particular element. (An element is thus a Carbonate A general term for a chemical compound
substance in which all of the atoms have the same atomic formed when carbon dioxide dissolved in water combines
number.) with oxides of calcium, magnesium, potassium, sodium,
and iron. The most common carbonate minerals are calcite
Aulocogen The failed arm of a triple junction rift. (which forms the carbonate rock limestone) and dolomite.
Australopithecines A general term applied loosely to
Carbonization The concentration of carbon during
Pliocene and early Pleistocene primates whose skeletal fossilization.
characteristics place them between typically ape-like indi-
viduals and those more obviously human. Carnosaurs Very large theropods with short necks and
Autotroph An organism that uses an external source of small forelimbs.
energy to produce organic nutrients from simple
inorganic chemicals. Cast (natural) A replica of an organic subject, such as a
fossil shell, formed when sediment fills a mold of that
Bacteria Unicellular, prokaryotic microorganisms belong- object.
ing to the Kingdom Monera. One of the three great
domains of organisms that include also the Archaea Catskill delta A build-up of Middle and Upper Devonian
and the Eukarya. clastic sediments as a broad, complex clastic wedge
derived from the erosion of highland areas formed largely
Basin A depressed area that serves as a catchment area for during the Acadian orogeny.
sediments (basin of deposition). A structural basin is an
area in which strata slope inward toward a central loca- Ceboidea The New World monkeys, characterized by
tion. Structural basins tend to experience periodic down- prehensile tails, and including the capuchin, marmoset,
sinking and thus receive a thicker and more complete and howler monkeys.
sequence of sediments than do adjacent areas.
Centrifugal force The apparent outward force experi-
Belemnites Members of the molluscan Class Cephalo- enced by an object moving in a circular path. Centrifugal
poda, having straight internal shells. force is a manifestation of inertia, the tendency of moving
things to travel in straight lines.
Benioff seismic zone An inclined zone along which fre-
quent earthquake activity occurs and that marks the Ceratites One of the three larger groups of ammonoid
location of the plunging, forward edge of a lithospheric cephalopods having sutural complexity intermediate
plate during subduction. between goniatites and ammonites.

Benthic Pertaining to a bottom-dwelling organism. Ceratopsians The quadrupedal ornithischian dinosaurs
Bentonite A layer of clay, presumably formed by the characterized by the development of prominent horns
on the head.
alteration of volcanic ash.
Beta particle A charged particle, essentially equivalent to Ceratosaurs Primitive theropods appearing first in the
Early Triassic.
an electron, emitted from an atomic nucleus during
radioactive disintegration. Cercopithecoidea The Old World monkeys (of Asia,
Bioturbation The disturbance of sediment by burrowing, southern Europe, and Africa), including macaques, gue-
boring, and sediment-ingesting organisms. nons, langurs, baboons, and mandrills.

Cetaceans The group of marine mammals that includes Glossary b G3
whales and porpoises.
Contact metamorphism The compositional and textural
Chalicotheres Extinct perissodactyls having robust claws changes in a rock that result from heat and pressure
rather than hoofs. emanating from an adjacent igneous intrusion.

Chalk A soft, white, fine-grained variety of limestone Convergence (in evolution) The process by which simi-
composed largely of the calcium carbonate skeletal larity of form or structure arises among different orga-
remains of marine microplankton. nisms as a result of their becoming adapted to similar
habitats.
Chert A dense, hard sedimentary rock or mineral com-
posed of submicrocrystalline quartz. Unless colored by Cordaites A primitive order of tree-like plants with long,
impurities, chert is white, as opposed to flint, which is blade-like leaves and clusters of naked seeds. Cordaites
dark or black. were in some ways intermediate in evolutionary stage
between seed ferns and conifers.
Chlorophyll The catalyst that makes possible the reaction
of water and carbon dioxide in green plants to produce Core The central part of the Earth that lies beneath the
carbohydrates. Photosynthesis is the reaction. mantle.

Choanichthyes That group of fishes that includes both Coriolis effect The deflection of winds and water currents
the dipnoans (lungfishes with weak pelvic and pectoral to the right in the Northern Hemisphere and to the left in
fins) and crossopterygians (lungfishes with stout lobe- the Southern Hemisphere as a consequence of the Earth’s
fins). rotation.

Chondrichthyes The broad category of fishes with carti- Correlation Determining strata that are equivalent in age
laginous skeletons that is exemplified by sharks, skates, but from different locations.
and rays.
Cosmic rays Extremely high-energy particles, mostly pro-
Chondrites Stony meteorites that contain rounded silicate tons, that move through the galaxy and frequently strike
grains or chondrules. Chondrules are believed to have the Earth’s atmosphere.
formed by crystallization of liquid silicate droplets.
Craton The long-stable region of a continent, commonly
Chromosome A thread-like, microscopic body composed with Precambrian rocks either at the surface or only thinly
of chromatin. Chromosomes appear in the nucleus of the covered with younger sedimentary rocks.
cell at the time of cell division. They contain the genes.
The number of chromosomes is normally constant for a Cratonic sequence A sequence of strata recording a com-
particular species. plete transgressive-regressive cycle on the craton.

Chromosphere One of the concentric shells of the Sun, Creodonta Primitive, early, flesh-eating placental
lying above the photosphere and telescopically visible as a mammals.
thin, brilliant red rim around the edge of the sun for a
second or so at the beginning and end of a solar eclipse. Crinoidea A taxonomic class of the Phylum
Echinodermata.
Cladistic phylogeny An approach to biologic classifica-
tion in which organisms are grouped according to simi- Crinoids Stalked echinoderms with a calyx composed of
larities that are derived from a common ancestor. regularly arranged plates from which radiate arms for
gathering food.
Clade A group of organisms in which all members are
more closely related to each other than to any other Cross-bedding (cross-stratification) An arrangement
organisms. of laminae or thin beds transverse to the planes of
stratification. The inclined laminae are usually at incli-
Clastic texture Texture that characterizes a rock made up nations of less than 30A7 and may be either straight or
of fragmental grains such as sand, silt, or parts of fossils. concave.
Conglomerates, sandstones, and siltstones are clastic
rocks; the individual clastic grains are termed clasts. Crossopterygii That group of choanichthyan fishes ances-
tral to earliest amphibians and characterized by stout
Clastic wedge An extensive accumulation of largely clastic pectoral and pelvic fins as well as lungs.
sediments deposited adjacent to uplifted areas. Sediments
in the wedge become finer and the section becomes Crust (Earth) The outer part of the lithosphere; it aver-
thinner in a direction away from the upland source areas. ages about 32 kilometers in thickness.
The Queenston and Catskill “deltas” are examples of
clastic wedges. Crustacea A subphylum of the phylum Arthropoda that
includes such well-known living animals as lobsters and
Coelurosaurs The most birdlike of the theropod crayfishes.
dinosaurs.
Crystal form The characteristic crystal shape of a mineral.
Coccolithophorids Marine, planktonic, biflagellate, Curie temperature The temperature at which a cooling
golden-brown algae that typically secrete coverings of
discoidal calcareous platelets called coccoliths. mineral acquires permanent magnetic properties that
record the surrounding magnetic field orientation and
Colorado mountains Highlands uplifted in Pennsylva- strength at the time of cooling. Magnetic properties of a
nian time in Colorado. Sometimes inappropriately mineral above the Curie temperature will change as the
termed the “ancestral Rockies.” surrounding field changes. Below the Curie temperature,
magnetic characteristics of the mineral will not alter.
Conodont elements Small, tooth-like, stratigraphically Cyanobacteria Prokaryotic, photosynthetic microorgan-
useful fossils composed of calcium phosphate and found isms that possess chlorophyll and produce oxygen. For-
in Cambrian to Triassic rocks. Conodonts are elements of merly termed blue-green algae.
an apparatus used by primitive chordates in capturing and Cycadales A group of seed plants that were especially
chewing food. common during the Mesozoic and were characterized
by palm-like leaves and coarsely textured trunks marked
by numerous leaf scars.

G4 c Glossary Edentata An order of placental mammals that includes
extinct ground sloths and gyptodonts, as well as living
Cyclothem A vertical succession of sedimentary units armadillos, tree sloths, and South American anteaters.
reflecting environmental events that occurred in a con-
stant order. Cyclothems are particularly characteristic of Ediacaran biota The late Proterozoic fauna of multi-
the Pennsylvania System. cellular animals first discovered in Australia but subse-
quently found in rocks about 600 million years old in
Cystoids Attached echinoderms with generally irregular many continents.
arrangement and number of plates in the calyx and
perforated by pores or slits. Endemic population The native fauna of any particular
region.
Deccan traps A thick sequence (3200 meters) of Upper
Cretaceous basaltic lava flows that cover about 500,000 Entelodonts A group of extinct artiodactyls bearing a
kilometers2 of peninsular India. superficial resemblance to giant wild boars.

De collement The feature of stratified rocks in which Eon A major division of the geologic time scale. The
upper formations may become “unstuck” from lower Phanerozoic Eon comprises all of the geologic periods
formations, deform, and slide thousands of meters over from the Cambrian to the Holocene. The term is also
underlying beds. sometimes used to denote a span of 1 billion years.

Diatoms Microscopic golden-brown algae (chrysophytes) Epifaunal organisms Organisms living on, as distinct from
that secrete a delicate siliceous frustule (shell). in, a particular body of sediment or another organism.

Differentiation The process by which a planet becomes Epoch A chronologic subdivision of a geologic period.
internally zoned, as when heavy materials sink toward its Rocks deposited or emplaced during an epoch constitute
center and light materials accumulate near the surface. the series for that epoch.

Dinoflagellates Unicellular marine algae usually having Era A major division of geologic time, divisible into geo-
two flagella and a cellulose wall. logic periods.

Diploid cells Cells having two sets of chromosomes that Eukaryote A cell containing a true nucleus, enclosed
form pairs, as in somatic cells. within a nuclear membrane, and having well-defined
chromosomes and cell organelles.
Dipnoi An order of lungfishes with weak pectoral and
pelvic fins; not considered ancestral to land vertebrates. Eurypterids Aquatic arthropods of the Paleozoic, superfi-
cially resembling scorpions and probably carnivorous.
Disconformity A variety of unconformity in which bed-
ding planes above and below the plane of erosion or Eustatic Pertaining to worldwide simultaneous changes in
nondeposition are parallel. sea level, such as might result from change in the volume
of continental glaciers.
DNA (deoxyribonucleic acid) The nucleic acid found
chiefly in the nucleus of a cell that functions in the transfer Evaporites Sediments precipitated from a water solution as
of genetic characteristics and in protein synthesis. a result of the evaporation of that water. Evaporite minerals
include anhydrite gypsum (CaSO4) and halite (NaCl).
Docodonts A group of small, primitive Late Jurassic mam-
mals possibly ancestral to the living monotremes. Evolution The continuous genetic adaptation of orga-
nisms or species to the environment.
Dolomite (or dolostone) A carbonate sedimentary rock
of which more than 50 percent is the mineral dolomite Exotic terranes Crustal fragments that have been moved
CaMg (CO3)2. from their place of origin by seafloor spreading and
accreted onto the margin of another plate or continent.
Domain A major taxonomic division ranking higher than a Once accreted, they differ from surrounding terranes and
kingdom. The three domains are the Archaea, Bacteria, are therefore dubbed “exotic.”
and Eukarya.
Facies A particular aspect of sedimentary rocks that is a
Dome An upfold in rocks having the general configuration direct consequence of sedimentation in a particular dep-
of an inverted bowl. Strata in a dome dip outward and ositional environment.
downward in all directions from a central area. An exam-
ple is the Ozark dome. Fault A fracture in the Earth’s crust along which rocks on
one side have been displaced relative to rocks on the other
Drift An accumulation of clastic sediment transported and side.
deposited by a glacier.
Felsic Term used to describe light colored igneous rocks
Dryopithecine In general, a group of lightly built pri- having the general composition of granite.
mates that lived during the Miocene and Pliocene in
mostly open savannah country and that includes Dryo- Fermentation The partial breakdown of organic com-
pithecus, a form considered to be in the line leading to pounds by an organism in the absence of oxygen. The
apes. final product of fermentation is alcohol or lactic acid.

Dynamothermal (regional) metamorphism Metamor- Filter-feeders Animals that obtain their food, which usu-
phism that has occurred over a wide region, caused by ally consists of small particles or organisms, by filtering it
deep burial and high temperatures associated with pres- from the water.
sures resulting from overburden and orogeny.
Fissility That property of rocks that causes them to split
Echinoderms The large group (phylum Echinodermata) into thin slabs parallel to bedding. Fissility is particularly
of marine invertebrates characterized by prominent pen- characteristic of shale.
tamerous symmetry and a skeleton frequently constructed
of calcite elements and including spines. Cystoids, Flood basalts Regionally extensive layers of basalt that
blastoids, crinoids, and echinoids are examples of originated as low-viscosity lava pouring from fissure
echinoderms. eruptions. The lavas of the Columbia Plateau and the
Deccan Plateau are flood basalts.