Encyclopedia of Dinosaurs Prehistoric Life

SOUTH AMERICAN HOOFED MAMMALS

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

249

MAMMALS AND THEIR ANCESTORS Arsinoitherium
Two smaller
URANOTHERES horns grew
from the back
ONE OF THE MOST PECULIAR groups of mammals is the Uranotheria, of the skull.

a collection of plant-eating, hoofed mammals that includes elephants,
seacows, and hyraxes. It might seem strange that these very different
creatures are thought to be related, but they share features not seen
in other mammals. The earliest members of these groups seem to
have been similar in appearance. The first elephants, for example,
were not giant creatures with trunks, but dog-sized animals probably
similar to modern-day hyraxes. In fact, hyraxes may show how the
earliest uranotheres lived – as small, grazing plant eaters. A later
group of uranotheres, called the tethytheres, evolved an amphibious
lifestyle. Some of these became committed to life in water and
eventually evolved into the first seacows.

Arsinoitherium had a
comparatively small
and simple brain.

Males had larger
and more pointed
horns than females.

Arsinoitherium’s teeth
had tall crowns and could
have been used to chew
very tough plant material.

ARSINOITHERIUM

Scientific name: Arsinoitherium ARSINOITHERES
Size: 12 ft (3.5 m) long
Diet: Tough leaves and stems These rhinoceros-like uranotheres lived in Asia,
Habitat: Woodland, wooded grassland Europe, and Africa 40–30 million years ago, in
Where found: Egypt and Oman the Eocene and Oligocene epochs. The best-
Time: Late Paleogene (Eocene) known arsinoithere is Arsinoitherium –
Related genera: Crivadiatherium, Paleoamasia a large, heavy animal with two massive horns on
its skull. The largest individuals of Arsinoitherium
Cambrian 542–488.3 Ordovician 488.3–443.7 (probably old males) were about the size of
small elephants. Unlike rhinoceros horns,
arsinoithere horns were hollow. They have
grooves on their surface, showing that there
were blood vessels on the outside, and that
the horns were probably covered in skin.

Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

250

URANOTHERES

Its shoulders Tusklike
were massive front teeth
and powerfully Arsinoitheres probably
muscled. digested their food
in an enormous hind
gut region.

Short, stocky
limbs

HYRAXES Kvabebihyrax

Modern hyraxes are small African mammals that
look like guinea pigs. Fossil hyraxes, however,
were quite different and came in a huge range
of shapes and sizes. Kvabebihyrax, shown here,
was the shape of a hippopotamus and may have
been amphibious. Titanohyrax was the size of a
small rhinoceros. Antilohyrax was a long-legged
runner resembling an antelope. Other fossil
hyraxes had long heads and would have looked
similar to modern-day pigs.

Arsinoitherium’s limbs
were stout and heavy.

Each foot had five blunt
toes, each tipped with
a small hoof.

Broad, heavy It had tusklike front
body teeth and cylindrical
chewing teeth.

DESMOSTYLIANS The front legs
Desmostylians, such as Paleoparadoxia, were may have been
sea-dwelling uranotheres. They lived on the used as paddles
edges of the Pacific Ocean during Oligocene when swimming.
and Miocene times (33.9–5.3 million years
ago) and probably fed on seaweeds. Skeleton of Paleoparadoxia
Desmostylians perhaps looked like a cross
between a hippopotamus and a walrus.
Although they lived mainly in the sea, they
could probably walk clumsily on land.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present

MESOZOIC 251–65.5 MYA CENOZOIC 65.5 MYA–present

251

MAMMALS AND THEIR ANCESTORS In Hipparion a large
bony pocket called the
HORSES preorbital fossa grew
on the side of the
PERISSODACTYLS ARE A GROUP of snout. This was larger
hoofed, odd-toed, plant-eating in males than females,
mammals, and include horses, though its function
tapirs, rhinoceroses, and remains unknown.
brontotheres. Horses, the most TEETH FOR GRASS-EATING
suited to open grasslands, Advanced horses, such as
appeared in the Eocene Hipparion, had large, high-
(55.8–33.9 million years ago) crowned molar teeth with
and about eight species of them complicated chewing surfaces
survive today. Successive groups made up of loops of enamel.
of horse species evolved Their premolars became
different features and body large and squarish and came
sizes to suit their environments. to look like the molars. These
Hipparion, shown here, was one powerful, resistant teeth allowed
of several species of three-toed advanced horses to eat rough
horse that lived on the grasses, although they may
Northern Hemisphere initially have evolved in
grasslands during the response to the accidental
Miocene (23–5.3 chewing of sand and grit.
million years ago).

Life in open, grassland
environments favored the
evolution of large body size
and long limbs in horses.

THREE-TOED FEET
Like modern horses, Hipparion
was a grassland animal. Earlier
horses were probably inhabitants
of forests. Unlike modern horses,
which only have one toe on each
foot, Hipparion had three-toed
feet. However, most of its weight
was borne on the enlarged
central toe. Hipparion and its
relatives were distant cousins
of horses such as Merychippus,
which were the probable
ancestors of modern horses.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

252

HORSES

HIPPARION

Scientific name: Hipparion Modern horses have special
Size: 5 ft (1.5 m) long locking mechanisms, called
Diet: Leaves and grasses stay apparatus, on their
Habitat: Grasslands, open woodlands limb bones that allow them
Where found: North America, Europe, Asia, to remain standing with
and Africa a minimum of effort.
Time: Neogene (Miocene–Pleistocene) Hipparion did not
Related genera: Cormohipparion, Nannippus, have stay apparatus.
Neohipparion

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

253

MAMMALS AND THEIR ANCESTORS

BRONTOTHERES AND CHALICOTHERES
THESE TWO GROUPS OF CREATURES were odd-toed hoofed mammals,
Weak teeth suggest
or perissodactyls. Brontotheres were large, rhino-like animals known that brontotheres
only from North America and Asia in the Eocene (53–33.7 million mostly ate
years ago). Early brontotheres were about the size of sheep, but soft leaves.
later ones were giants, up to 8 ft (2.5 m) tall at the shoulder. Some
sported horns on the end of their snouts that grew in V or Y shapes.
Chalicotheres were horselike perissodactyls with long forelimbs and
curved claws on their fingers and toes. First appearing in the Eocene
in Asia and Europe, they later spread to Africa and North America
and survived into the early Quaternary.

BRONTOTHERE HORNS SKULL OF BRONTOPS
As brontotheres evolved, their horns became larger. Later brontotheres, such as
In later brontotheres, males had larger horns than Brontops, had very shortenend
females. This suggests that brontothere males used Injuries found on skulls and faces and eyes positioned close
their horns for displaying and fighting, like the two ribs suggest that brontotheres to the nose. Brontops had two
male Brontops shown here. Early brontotheres had fought each other with their short horns that stuck upward
horns, perhaps for dominance, and outward.

tusk-like front teeth, but territory, or mating rights.

Brontops and other later
brontotheres lacked
these and instead
had a mobile
upper lip.

The surface texture Powerful muscles were
of the horns shows attached to the massive
that they were spines on the shoulder
covered in skin. vertebrae and formed
a prominent hump.
In some brontotheres
one of the wrist bones,
a bone called the
trapezium, was absent.
No one knows why.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

254

BRONTOTHERES AND CHALICOTHERES

BRONTOPS Its skeleton
suggests that
Scientific name: Brontops Moropus could
Size: 17 ft (5 m) long stand up on its
Diet: Leaves
Habitat: Open woodland back legs.
Where found: Western North America
Time: Paleogene (Eocene) Its long, flexible
Related genera: Menops, Megacerops, neck allowed
Duchesneodus Moropus to
reach up into
Brontops branches.

The powerful
front legs were
longer than the
back legs.

The hip bones were Moropus could
very broad, probably hold its claws up
to help support the off the ground
weight of the body. when it walked.

A CLAWED “HOOFED MAMMAL”
Moropus was a chalicothere from North America. Like all
chalicotheres, it had massive, powerful front legs and curving
claws on its hands. Chalicotheres may have been digging animals
that fed on roots and tubers. However, their wrists were not very
mobile, and their teeth lack the wear marks normally created by
soil and grit. It is more likely that chalicotheres were browsers
that pulled branches down from trees.

Brontothere tails
probably ended
in a tuft of hairs.

Giant brontotheres LAST OF THE
had stout, short BRONTOTHERES
limbs suited to Embolotherium and
carrying the its relatives were an
immense weight advanced group of
of their bodies. brontotheres, found
only in Asia. They were
related to Brontops.
Embolotherium was one of
the last and largest of the
brontotheres. It was
similar in size to Brontops,
but was equipped with a
large, forked nose horn.

Its broad mouth
contained small,
rounded incisor teeth.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

255

MAMMALS AND THEIR ANCESTORS

RHINOCEROSES ELASMOTHERIUM
The surviving species of rhinoceros are members of
TODAY THERE ARE FIVE SURVIVING SPECIES of the rhinocerotid group. The biggest rhinocerotid was
Elasmotherium, which reached 16 ft (5 m) in length and
rhinoceros. They are plant-eaters with horns had an immense conical horn 6 ft 6 in (2 m) tall on its
made from keratin – the same structure that forehead. Elasmotherium lived in the Pleistocene
skin, nails, and claws are made from. Fossil (1.81–0.01 million years ago).
rhinoceroses were diverse and evolved many
different lifestyles and body shapes. Perhaps
the most primitive rhinoceroses were the
hyracodontids, or running rhinoceroses.
These were hornless, long-legged creatures
with simple teeth suited for browsing.
Another family, the amynodontids, included
amphibious rhinoceroses with short mobile
trunks, like the trunks of modern-day tapirs.
Amynodontids appear to have been very
primitive rhinoceroses, and it has even been
suggested that they are not rhinoceroses
at all, but part of the tapir group of
perissodactyls instead.

THE BIGGEST LAND MAMMAL

Paraceratherium was a gigantic hyracodontid rhinoceros. In
contrast to the small early hyracodontids, Paraceratherium
was 18 ft (6 m) tall at the shoulder and weighed around
15.7 tons (16 tonnes), making it the biggest land
mammal of all time. Its skull alone was about
4 ft (1.3 m) long. Paraceratherium was
probably a browser that ate leaves
from the tops of trees.

PARACERATHERIUM

Scientific name: Paraceratherium Despite its great size,
Size: 9 m (30 ft) long Paraceratherium had
Diet: Leaves and twigs long, slim legs and
Habitat: Open woodland could probably run.
Where found: Eastern Europe, Asia
Time: Palaeogene–Neogene
(Oligocene–Miocene)
Related genus: Forstercooperia

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

256

RHINOCEROSES

Paraceratherium Its skull structure
Hollows in the sides suggests that
of Paraceratherium’s Paraceratherium had
back bones made a flexible upper lip.
them light but strong.

Its long neck enabled WOOLLY RHINOCEROS
Paraceratherium to Coelodonta, the woolly rhinoceros of Asia and
browse from trees. Europe, lived in the Pleistocene (1.75–0.01
Some Teleoceras million years ago). It is known from bodies
species had a preserved in frozen soil and from prehistoric
flexible upper lip. cave paintings. We therefore have a good idea
of what Coelodonta would have looked like. It
had two large horns, a hump over its shoulders,
thick stocky limbs, and long, dark fur.
Barrel-shaped
body

Tall cheek teeth Teleoceras probably
for chewing walked along the
tough grass bottom of rivers.

Three stout toes LIVING LIKE A HIPPOPOTAMUS
supported its Teleoceras was a long-bodied rhinoceros from North America
weight. that lived in the Miocene (23.5–5.3 million years ago). It had
very short legs and a small nose horn. Teleoceras had long teeth,
which show that it was a grass-eater. It probably lived like a
hippopotamus, wallowing in water but grazing on land at night.
Its fossils are frequently found in the beds of ancient streams.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

257

MAMMALS AND THEIR ANCESTORS

PROBOSCIDEANS
THE TWO MODERN-DAY species of elephant are the living representatives of a
much larger group of hoofed mammals, called the proboscideans.
The earliest known proboscidean was Phosphatherium from the Paleocene Phiomia
probably had
a short trunk.
(65–56 million years ago). It weighed only about
33 lbs (15 kg) and was just 2 ft (60 cm) tall at
the shoulder. Later proboscideans
increased in size and evolved straight,
columnlike legs. They also grew
massive tusks in their upper jaws,
which they used for fighting and
gathering food. The structure of their
PHIOMIA
skulls shows that nearly all fossil This primitive proboscidean
proboscideans had a trunk. lived in northern Africa
during the Oligocene
(33.9–23 million years ago).
Phiomia was larger than
Moeritherium but still only
about as big as a large
modern horse. It had
MOERITHERIUM columnlike legs, a shorter
neck, and a much bigger skull
One of the most primitive known proboscideans is Moeritherium. than more primitive elephants.
It lived in Africa in the Eocene. Moeritherium’s skull indicates Like later elephants, Phiomia
that it had an enlarged upper lip, but experts do not know had air-filled spaces, called
whether this was a true trunk. Its bulky body was similar in diploe, in its skull. This meant
shape to a hippopotamus, and its legs were short. These features that its skull was light, despite
suggest that Moeritherium wallowed in lakes and rivers, perhaps its size.
feeding on water plants. Enlarged
incisor teeth in both the
upper and lower jaws
formed small tusks
that probably
protruded
from its
mouth.

Primitive proboscideans like
Moeritherium had not yet
developed the columnlike
legs of an elephant.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

258

ELEPHANTS

Gomphotherium SHOVEL-TUSKERS
was about as big Like nearly all primitive proboscideans, Phiomia
as an Asian elephant. had tusks in both its upper and lower jaws. Its
lower jaw was long and had flattened, square-
tipped tusks. This formed a shovel-shaped jaw
that could have been used to scoop up water
plants, or cut branches or bark from trees.
Later, more advanced kinds of proboscidean,
such as Gomphotherium, had
similar lower jaws.
Skull of
Phiomia

GOMPHOTHERIUM DEINOTHERES
A successful group of elephants called These strange proboscideans had no
gomphotheres spread around the world tusks in their skulls and two down-
in the Miocene and Pliocene (23–1.8 curved tusks in their lower jaws.
million years ago). Gomphotheres, These may have been used to dig
such as Gomphotherium, inhabited up roots, strip bark, or wrench
marshes, grasslands, and branches down from trees.
forests. Gomphotherium’s upper Deinotheres seem to have
jaw tusks were probably used had shorter trunks than
for fighting and display and, living elephants.
as in living elephants, were
larger in males than in Deinotherium was
females. Elephants similar 13 ft (4 m) tall at
to Gomphotherium were the the shoulder.
ancestors of mammoths and
of modern-day elephants. MOERITHERIUM

The enlarged upper Scientific name: Moeritherium
lip and nose may Size: 10 ft (3 m) long
have formed a Diet: Water plants
very short trunk. Habitat: Lakes, rivers, riverside forest
Where found: Northern Africa
Moeritherium’s neck was Time: Paleogene (Eocene–Oligocene)
longer than that of more Related genus: Phosphatherium
advanced proboscideans.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

259

MAMMALS AND THEIR ANCESTORS

PLATYBELODON

PLATYBELODON WAS A WIDESPREAD “shovel-tusker”

gomphothere. It had a long, scooplike tip to its lower jaw,
formed by the tusk and mandible. In some specimens the
lower jaw curved downward along its length, while in others
it was straighter and curved upward at the tip. Platybelodon
was once thought to have lived in marshes, where it used its
lower jaw to scoop up water plants. Wear patterns on its tusks
suggest instead that Platybelodon mostly lived in grasslands
and forests and cropped tough vegetation from trees.

A FLEXIBLE TRUNK
Old reconstructions of Platybelodon show it with a
short, wide trunk that would not have been very
flexible. This is because the reconstructions were
based on evidence from the more primitive Phiomia.
The nasal openings in Phiomia’s skull show that its
trunk was short and poorly developed. However,
Platybelodon had the same kind of nasal openings as
modern elephants. Like modern elephants therefore,
Platybelodon probably had a long, flexible trunk.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

260

PLATYBELODON

PLATYBELODON

Scientific name: Platybelodon
Size: 3 m (10 ft) tall at shoulder
Diet: Leaves, grasses, bark
Habitat: Grasslands, forests
Where found: North America, Africa,
Asia, Europe
Time: Neogene (Miocene–Pliocene)
Related genera: Amebelodon, Torynobelodon

LOWER JAW
The wear marks on
Platybelodon’s lower jaw tusks
show that vegetation was often
pulled across the tips of the
tusks. Platybelodon probably
used the tusks as blades. It
would have grabbed a branch
with its long trunk and pulled it
repeatedly across the tusks until
they sliced through the wood. It
seems that most of this branch-
cutting happened where the
two tusks touched one another,
as this is usually the most
heavily worn area.

LEGS AND FEET
Like all advanced elephants, Platybelodon had straight legs.
Its knees were positioned directly above its ankles, so
each leg formed a column beneath its body. Platybelodon’s
ankles were very close to the ground because the bones
that formed its feet were very short. Fatty pads under its
feet supported the foot bones and helped to spread the
animal’s great weight as it walked.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

261

MAMMALS AND THEIR ANCESTORS Mammoth hair, found on
the frozen specimens, can
MAMMOTHS be up to 3 ft (90 cm) long.

THE EIGHT SPECIES OF MAMMOTH were all true elephants, closely related Shoulder hump

to the two living species. Mammoth genetic material, or DNA, was
discovered in 1994 and found to be almost identical to that of living
elephants. The woolly mammoth (Mammuthus primigenius) is perhaps
the most famous fossil animal from the Pleistocene (1.75–0.01 million
years ago). An inhabitant of the cold Ice Age grasslands, it had a shaggy
coat, huge, curving tusks, and a tall, domed skull, but was small compared
to some other extinct elephants. As in living elephants, male mammoths
probably wandered on their own and fought for dominance with
their tusks. Some males even died locked in combat and have been
preserved this way as fossils. The last mammoths, a population
of dwarf woolly mammoths, lived on Wrangel Island north of
Siberia and died out only 4,000 years ago.

WOOLLY MAMMOTH Mammuthus primigenius
These mammoths lived in
herds and fed on grasses
and other small plants,
which they plucked with Both male and female woolly
the two “fingers” on the mammoths had long, curving
tusks. They used their tusks
in combat and display, and
tips of their trunks. as tools for gathering food.
Several woolly mammoths
have been found preserved
in the frozen ground of
Siberia. Their fur, skin,
muscles, and even their
stomach contents are still intact.
These frozen specimens show that,
unlike living elephants, mammoths
had very short tails. This is probably because
a long tail would be vulnerable to frostbite.

DIMA THE MAMMOTH Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian
Dima was the name given to
a frozen male baby woolly
mammoth, recovered in
1977 on the bank of the
Berelekh River, Russia,
and preserved in a
remarkably complete
condition. How Dima
died has been the subject
of debate. It has been
suggested that he drowned, fell into
a crack in the frozen ground, or
became caught in wet mud. X-rays
show that Dima had not yet grown
the domed skull and tall shoulder
hump seen in adult mammoths.
Cambrian 542–488.3 Ordovician 488.3–443.7

PALEOZOIC 542–251 MYA

262

MAMMOTHS

CAVE PAINTINGS WOOLLY MAMMOTH
About 400 prehistoric cave
paintings and sculptures of Scientific name: Mammuthus primigenius
woolly mammoths are known. Size: 11 ft (3.3 m) tall
Most have been found in French Diet: Grasses and other plant material
or Spanish caves and are about Habitat: Woodlands and grasslands
30,000 years old. The paintings Where found: North America, Europe, Asia
show mammoths with the same Time: Late Neogene (Pleistocene–Holocene)
features as the mammoths Related genus: Elephas (includes
preserved in frozen ground, living elephants)
such as a shoulder hump and
small, rounded ears. Some
paintings depict mammoths
moving in groups while others
show mammoths fighting.

The tusks
were so long
and curved
that they
crossed over.

Huge
columnlike
limbs
supported
its weight.

IMPERIAL MAMMOTH
Mammuthus imperator (Imperial mammoth) was
a giant North American Pleistocene mammoth
and one of the biggest elephants that ever
lived. It was 12 ft (3.7 m) tall at the shoulder
and its huge, curving tusks could be 14 ft
(4.3 m) long. Many fossils have been found
in California, where this mammoth inhabited
warm grassland and woodland environments.
Warm-weather mammoths probably lacked
the furry coats of their cold-climate cousins.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

263

MAMMALS AND THEIR ANCESTORS

PIGS, HIPPOS, AND PECCARIES
THE LARGEST AND MOST SUCCESSFUL group of hoofed
mammals are the artiodactyls, or even-toed hoofed DAEODON
mammals. All artiodactyls have distinctive ankle
and foot bones that allow many of them to run fast.
Their feet are symmetrical, and most forms have two
or four toes, hence the group’s name. Artiodactyls
include three major groups that all first appeared in
the Eocene. The first group is the suiforms, including
pigs, hippopotamuses (hippos for short), peccaries,
and various extinct relations. Unspecialized teeth
and flexible snouts have allowed them to become Scientific name: Daeodon
omnivores that can eat most kinds of plant material Size: 10 ft (3 m) long

Diet: Vegetation, carrion, smaller animals

and fungi, as well as carrion and small animals. Many Habitat: Grasslands, open woodland

suiforms had, or have, large fang- or tusk-like teeth Where found: North America
used for fighting and display. These tusks have Time: Paleogene–Neogene (Oligocene–Miocene)
become massively enlarged in the hippos. The Related genera: Archaeotherium, Choerodon

second artiodactyl group, the tylopods, includes
the camels. The third group, the pecorans,
includes giraffes, deer, and cattle. Skeleton of
Entelodonts had small Archaeotherium

brains, but parts of the
brain devoted to smell
HIPPOPOTAMUSES were well developed.
The first hippos appeared in the Late Miocene. Two kinds
survive today – the large, amphibious Hippopotamus and
the small, land-living Hexaprotodon. The recently extinct
Hippopotamus lemerlei was a pygmy river-dwelling hippo from Bony cheek flanges
Madagascar. Hippos have huge, curving tusks at the front of were especially large,
the mouth. These are larger in males than females and are with swollen ends.

used in fighting and displaying. Genetic
studies suggest that hippos may
be related to whales, but
this is controversial.

Eyes located on ANCIENT BEAST
top of the head Entelodonts were
pig- to bison-sized
Amphibious hippos suiforms known
have elongated snouts from Eocene and
and lower jaws. Miocene Europe,
Skull of Hippopotamus lemerlei Asia, and North
America. They had long legs and deep
bodies. Their huge skulls have bony
bumps on the cheeks and lower jaws,
crushing teeth, and huge, curving canine
teeth. Archaeotherium was a successful pig-
sized entelodont that lived across North
America and Asia.

Incisors protrude Unlike many other suiforms,
forward, and can entelodonts had only two
be used for digging. toes on each foot.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

264

PIGS, HIPPOS, AND PECCARIES

Macrogenis Powerful neck tendons
skull attached to the shoulder
spines helped to support head.

Elongated bony
spines grew from
shoulder vertebrae.

PECCARIES Daeodon
Another group of suiforms,
which appeared in the Late Eocene
(around 40 million years ago), and
lived mostly in North America, are
the peccaries. They survive to the
present as three species. Peccaries look
much like pigs and live in similar ways.
They have large, vertical canine teeth.
Some extinct peccaries, like the Late
Miocene Macrogenis, had massive
triangular protrusions of bone
growing out from their cheeks.

Skull bumps
became larger
with age.

Curving canine
teeth with
serrated edges
Big crushing molars
suggest Daeodon
ate bones

KILLER BUFFALO PIG Unlike in smaller Unlike in smaller
entelodonts, the lower entelodonts, the
Daeodon, formerly called Dinohyus, leg bones of Daeodon lower leg bones of
is one of the biggest, best known, and were fused together Daeodon were fused
last of the entelodonts. Like others of its group, for strength. together for strength.
it had tall shoulders, a deep body, and long legs.
The bumps on its skull and jaws were probably
used for fighting – some fossil specimens have
wounds that appear to have resulted from such
battles. The bony bumps in Daeodon were actually
smaller than those of most other entelodonts,
though they were still prominent. The teeth
and muscle scars of Daeodon suggest that it was
an omnivore, easily able to break bones and
eat animal carcasses. Entelodonts may have
been scavengers, finding their food in a
similar way to modern hyenas.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Palaeogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

265

MAMMALS AND THEIR ANCESTORS

CAMELS
CAMELS AND THEIR RELATIVES EVOLVED in the Eocene
HIGH CAMEL
(56–34 million years ago), and include nearly 100 fossil
species. Although modern camels inhabit deserts, they Scientific name: Aepycamelus
were once abundant grassland and woodland herbivores. Size: 2 m (7 ft) tall at shoulder
Two groups of artiodactyls – the bovoids and the camels Diet: Leaves from trees
and relatives – evolved a special way of digesting plant Habitat: Open woodland, grassland with trees
material called rumination. Once swallowed, food passes Where found: North America
to the first of three or four stomach chambers, and is Time: Neogene (Miocene)
later regurgitated to be chewed a second time (“chewing Related genera: Oxydactylus, Hesperocamelus
the cud”). In each stomach chamber, microorganisms
break down the plant material further. Ruminant
mammals recycle urea, one of the body’s waste products,
and use it to feed these microorganisms. As a result,
less urine is produced, and less water wasted, which
is why ruminants have adapted to dry environments
like deserts more successfully than
other hoofed mammals.

Stenomylus
probably lived
in large herds.

Skull very short
compared to
other camels

Long, slender
legs would
have made
Aepycamelus
a fast runner.

NARROW TOOTH When standing Aepycamelus walked
The six living camel species are native to Africa, Asia, and South Stenomylus was less on the whole length of
America. However, most of camel history occurred in North America, than 3 ft 3 in (1 m) its toes, unlike earlier
and camels still lived here as recently as 11,000 years ago. The first tall at the shoulder. Stenomylus.
camels were small, and perhaps lived like modern gazelles. Stenomylus
from the Oligocene (around 30 million years ago) was a small
early camel with enormous chewing teeth. Unlike advanced camels,
Stenomylus had pointed hooves and walked on the tips of its toes.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

266

CAMELS

Features of teeth and
FEEDING STRATEGIES skull suggest a closer
Living camels are grazers that relation to living llamas Pointed
mostly eat grasses. The skulls than to modern camels. front teeth
were small.
and teeth of fossil camels,
however, show that many
of them were browsers,
feeding on shrubs and trees.
Oxydactylus from Miocene GIANT GIRAFFE CAMEL
North America had long
legs and a long neck. Aepycamelus (“high camel”)
Perhaps Oxydactylus fed was a large camel with
on trees by standing tremendously long leg and
tall on its back legs
like the modern neck bones. It was probably
Gerenuk antelope. a browsing herbivore that,
Feeding Gerenuk like modern giraffes, fed from trees. Eight
Aepycamelus species are known, each with a
slightly different skull and jaws. They inhabited
grasslands with scattered trees, and may have
become extinct as the tree cover gradually
disappeared. Aepycamelus probably shared
a number of features with living camels,
including a divided upper lip, a long, curved
neck, unusual two-toed feet, and legs that are
not joined by a sheet of skin to the side of the
body. Camels also have special fanglike teeth
Neck bones that the males use in fighting.
longer than
those of any
other camel

Front and back legs Fossil Oxydactylus foot
of camels are more Two “metapodial” bones
equal in size than are fused together in
they are in other advanced camels.
hoofed mammals. Advanced camels
like this have only
two toes.

Like living kinds Primitive Eocene camels
of camel, fossil still had four toes.
species perhaps
had dense, CAMEL FEET AND WALKING STYLE
woolly fur. Advanced camels have unique feet. Unlike other
artiodactyls, they do not walk on the tips of their
As in modern toes, but on the whole length of their toes. Soft toe
camels, two pads help them walk on rocks or sand with ease.
main hand Camels walk using a technique called pacing. Both
bones were legs on one side of the body move in the same
fused together. direction at once.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

267

MAMMALS AND THEIR ANCESTORS In the largest males,
the antlers spanned
DEER AND KIN 12 ft (3.7 m).
GIANT ANTLERS
SEVERAL NEW GROUPS OF SMALL, forest-dwelling The largest antlers of all time
belong to Megaloceros, a giant
herbivores diversified during the Miocene Pleistocene deer that was still alive
(23–5 million years ago). The spread of 9,000 years ago. Despite the huge
grasslands allowed some of them to move size of these antlers, microscopic
out of the forest, becoming larger and stress marks show that they were
more successful. Like bovoids, many used for fighting and not just
evolved horns or equivalent structures display. Antlers are shed each year
for fighting and displaying. The most and, except in reindeer, are grown
successful of these mammals were the only by males. Antlers may have
deer – antelope-like animals distinguished first developed from scar tissue
by their antlers. Early antlers were resulting from injuries.
simple in shape – any fighting was
probably done with fanglike teeth, and
some living deer still fight in this way.
Giraffids (the giraffes and their relatives)
were one of the first groups to move to the
grasslands and evolve large body size. Some
fossil giraffes were deerlike, and all possessed
bony horns called ossicones. Several other groups
of deerlike mammals, including the paleomerycids

and protoceratids, evolved their
own impressive bony horns.

Syndyoceras Protoceras
Synthetoceras

EARLY HORNS A dappled coat
The deerlike protoceratids may have helped
(“early horns”) lived in North Cranioceras to hide
America from about 45 to 4 million in dense foliage.
years ago, from the Eocene to the Pliocene. Male
protoceratids displayed some of the most spectacular and complex All weight
horns ever evolved. In earlier protoceratids, such as Protoceras, the was carried
horns looked most impressive in side view. Later kinds, including by the middle
Syndyoceras and Synthetoceras grew horns more suited for display two toes.
from the front. Protoceratids had stout limbs and bodies, and
their teeth suggest that they ate soft vegetation and they probably
had a flexible upper lip like a camel’s.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

268

DEER AND KIN

THREE-HORNED DEER RELATIVE Second Long rear Giraffokeryx restoration
pair of ossicones
Cranioceras was a paleomerycid – one of a group of
deerlike hoofed mammals that lived from about 34 to 4 ossicones
million years ago, from the Oligocene to the Pliocene. Many, on nose

but not all, paleomerycids had bony horns that grew
backward, forward, or upward from above their eyes. In the
group that includes Cranioceras, a third horn grew upward
and back from the rear of the skull. Healed injuries seen on
paleomerycid horns show that they were used for fighting –
probably to establish mating rights and social dominance. As
in most horned mammals, only males possessed horns.
While some paleomerycids had
long limbs and probably lived in
the open, Cranioceras and its Paleomerycid
relatives were short-legged horns may have
denizens of dense woodlands, been more
about 10 million years ago. Later like ossicones,
paleomerycids grew larger, but suggesting GIRAFFIDS
then smaller just before a close link Giraffokeryx was a primitive giraffid that lived
to giraffids. in Miocene and Pliocene Asia, Europe, and
Africa, around 5 million years ago. It had two
their final extinction. pairs of pointed, furry, hornlike structures called
ossicones. The giraffids are cud-chewing hoofed
mammals that probably share an ancestor with
bovoids. Only two survive today – the African
giraffe (Giraffa camelopardalis) and the Okapi
(Okapia johnstoni). As well as distinctive ossicones,
both use a flexible tongue to bring foliage to
the mouth. However, many other giraffids
thrived from the early Miocene era (around
20 million years ago) and the recent past. One
major group of extinct giraffids, the sivatheres,
had enormous branching ossicones, and would
have looked more like deer than giraffes.

CRANIOCERAS

Limbs were Scientific name: Cranioceras
not as long or Size: 1 m (3 ft) tall at shoulder
slim as those Diet: Leaves
of grassland- Habitat: Subtropical woodland
dwelling Where found: North America
relatives. Time: Neogene (Miocene)
Third horn Related genera: Procranioceras, Yumaceras
could have
been used for
display as well
as fighting.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

269

MAMMALS AND THEIR ANCESTORS

CATTLE, SHEEP, AND GOATS
CATTLE AND THEIR RELATIVES are
Sharp, strong horns
the most plentiful large, hoofed, that are never shed
grazing animals alive today. Wild
and domestic cattle, sheep, goats,
antelopes, and musk oxen (but not
the antelopelike pronghorns) are
grouped together as bovoids, named from
the Latin word for ox. All these animals
probably evolved more than 20 million years
ago from small, hornless, deerlike ancestors.
Early forms resembling gazelles gave rise to
huge variety, with more than 100 genera by about
two million years ago, but all bovoids share some
common features. These include strong, defensive
horns which never shed on the heads of both
sexes, and teeth and stomachs adapted for eating
and digesting grass. Legs and two-toed feet are also
designed for fast running or agile leaping to escape
enemies. The cattle family spread first through
Europe, Africa, and Asia. By one million years ago,
some crossed the Bering Land Bridge into North
America where bison, bighorn sheep, and Rocky Jaws have high-
Mountain goats persist today. crowned teeth, which
evolved for chewing.

PREHISTORIC ANIMALS IN CAVE PAINTINGS ANCESTRAL OX
An artist depicted this great ox on a cave wall at Lascaux
in southwest France some 15,000 years ago. At the time, Bos primigenius, also known as the
Old Stone Age hunter-gatherers hunted wild herds of aurochs, was the ancestor of most
cattle for their meat. Perhaps another 7,000 years went domesticated cattle. It was larger
by before people learned to tame and farm the least than modern cattle, wild and fierce,
fierce individuals for meat, milk, and hides. The old wild and roamed the forests of Europe,
cattle strain is now extinct, but millions of its descendants Asia, and Africa, dying out in recent
graze peacefully in pastures worldwide. times. The last wild aurochs was killed in
Poland in 1627. Bovoids such as Bos and
Bison priscus left large fossil horn cores of
bone. In life, horny sheaths covered these
cores, making the horns even longer.
Fossils of the prehistoric ox Pelorovis,
related to the modern African buffalo,
have 6 ft 6 in (2 m) horn cores. With the
addition of their sheaths, its horns could
have spanned as much as 13 ft (4 m). These
awesome horns were used by rival males for display
and fighting, as well as for self-defense. Although
these prehistoric creatures are no more, wild cattle
of several genera survive. The best known kinds are
bison, buffaloes, and yak.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

270

CATTLE, SHEEP, AND GOATS

Muscular neck Bos stood up to ANCESTRAL OX
and shoulders 6 ft 6 in (2 m) tall
at the shoulder.

Scientific name: Bos primigenus
Size: 10 ft (3 m) long
Diet: Plants
Habitat: Forest glades
Where found: Europe, Africa, Asia
Time: Neogene (Pliocene–Holocene)
Related species: Bison, Pelorovis

Branched horns
with sheaths shed
annually

Hind limbs with short
thigh bones, but long
shin and foot bones

Long foot
with high
ankle, a
design for
fast running

Sturdy limbs to Foot has two Tiny early
support weight large toes tipped pronghorn
EARLY SHEEP AND GOATS with hooves. Ramoceros
Goats and sheep, including PREHISTORIC PRONGHORN
mountain sheep like Ovis canadensis Ovis canadensis skull Miocene and Pliocene North America
shared a common ancestor with was home to the antelopelike pronghorn
other bovoids. This animal or antilocaprid family, of which only one
probably existed in the member now survives – the second fastest
Oligocene, more than mammal in the world. Ramoceros was a small,
20 million years ago. Its prehistoric relative of the living pronghorn.
descendants gave rise first to Its long, forked horns may have been used
antelopes, then to sheep and by rival males in pushing contests. Like other
goats, and finally to cattle. antilocaprids, Ramoceros shed the sheaths of
its horns every year, and new horns formed
from hair sprouting on the bony cores.
This difference between pronghorns
and cattle persuades many scientists
that these agile mammals may be
more closely related to deer.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

271

MAMMALS AND THEIR ANCESTORS

HOOFED PREDATORS

WHEN SOMEONE MENTIONS “HOOFED MAMMALS,” we tend to think

of unaggressive plant-eating creatures: cattle, antelope, and sheep.
Early in their evolution, however, the ancestors of these even-toed
hoofed mammals included very different creatures – the
so-called mesonychians. Like sheep or cows, these
had toes tipped with hooves, not claws. But instead of
molars shaped for munching leaves, the creatures
had massive teeth designed for slicing meat
or crushing bones. Mesonychians
looked rather like, and played
the same role as,
wolves, hyenas, and
bears. They lived
across Europe, Asia,
and North America
for around 30 million
years, from the middle
Paleocene (60 MYA)
to the early Oligocene
(30 MYA).

Long, narrow jaw with Toes tipped
teeth rather like a bear’s with short
hooves instead
Head broad at the back of long sharp
with powerful jaw muscles. claws

Andrewsarchus skull

Massive molars with blunt Long, curved, GIGANTIC OMNIVORE
cusps for crushing pointed canine tooth
for piercing flesh The enormous Andrewsarchus (“Andrews’ flesh-
eater”) lived in Eocene Mongolia more than
POWERFUL JAWS 40 million years ago, and was the biggest known
The skull of Andrewsarchus shows its powerful jaws and carnivorous land mammal of all time. Its skull
formidable collection of teeth. The canines at the front alone was 33 in (83 cm) long and 22 in (56 cm)
were long, curved, and piercing for delivering the killer bite wide. The rest of the skeleton has not been
to its prey. The back teeth were also pointed – the lower molars discovered, but its body probably grew up to
bladelike for cutting, and the upper molars broad, designed for 19 ft (6 m) long or even more. Andrewsarchus’s
crushing. Notches in the top and bottom teeth were much like jaws were equipped with long, sharp, curved canine
those in living carnivores, for gripping meat to tear it from the teeth, and massive, crushing back teeth, powerful
bone. The back teeth, however, were generally not as well- enough to have killed and crunched the bones of
designed for slicing flesh as those of modern carnivores. young hoofed mammals, but this enormous beast
was probably as unfussy about its diet as a grizzly
bear. It would have munched juicy leaves and
berries, insect grubs, and small rodents, as well as
scavenging from large corpses that it came across.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

272

HOOFED PREDATORS

Long, heavy body Skull shape shows Long, lean body
(exact shape is unknown) Mesonyx had shaped something
a strong bite. like a wolf’s

Like Mesonyx, MIDDLE NAIL
Andrewsarchus Mesonyx (“middle nail”) was a member of the
may have had mesonychids, the best-known mesonychian family.
a long tail. It was a wolflike predator from the Middle Eocene
Strong limbs must of Wyoming and East Asia (around 45 million years
have supported ago). Agile limbs made it a fast runner, and it probably
its great weight. hunted hoofed plant eaters, moving lightly on its toes,
not flat-footed like the less advanced mesonychians. Yet,
Andrewsarchus may instead of claws, Mesonyx’s toes ended in small hooves.
have been flat-footed, Its long skull had a crest above the braincase to anchor
like a bear. large jaw muscles and give it a powerful bite.

Archaeocetes skull

ANDREWS’ FLESH-EATER

Long, low, narrow
jaws like those
of mesonychians

Scientific name: Andrewsarchus WHALE ANCESTORS
Size: Up to 19 ft (6 m) long Mesonychians probably became extinct when outcompeted by
Diet: Meat, plants, insects new kinds of more efficient predators, including the ancestors
Habitat: Scrub and open woodland of carnivores alive today. Meanwhile, though, according to a once
Where found: East central Asia popular theory, they gave rise to a much longer-lived and more
Time: Paleogene (Eocene) successful group of mammals – the whales. The skulls and teeth
Related species: Eoconodon, Goniaconodon of early whales such as Archaeocetes strongly resemble those of
certain mesonychians. But other anatomical features and
molecular evidence place whales with the artiodactyls.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

273

MAMMALS AND THEIR ANCESTORS

EARLY WHALES Square tail vertebrae Long tail flukes
show that the tail provided the main
LIVING CETACEANS – whales, dolphins, and their kin – had flukes (fins swimming thrust.
along its sides)
are fish-shaped, with flipperlike
forelimbs, powerful fluked tails for Long tail
propulsion, and no hind legs. The
earliest Eocene whales were very different: Large hindlimbs Tiny, three-toed
they had four legs and ran around on land. made Ambulocetus hindlimbs would
Yet skeletons show some had started to swim a strong swimmer have projected
with an up and down motion of the tail. By the from sides.
end of the Eocene, fully aquatic whales like
Basilosaurus had evolved. Eocene whales were
predators that mostly inhabited shallow tropical seas.
They evidently descended from close kin of, or
actual, artiodactyls that had taken to foraging for
food in shallow water. Mesonychians’ skulls are
strikingly like those of the first whales, but early
whales’ ankle bones show features only seen in
artiodactyls. DNA studies even hint that whales
could have arisen from the artiodactyl group
that includes hippopotamuses.

Long skull, with
nostrils close to
the tip of snout

ECHOLOCATION AT WORK
Throughout their evolution, whales developed
a method called echolocation to gain a mental
picture of their surroundings. Many project
Ambulocetus probably noises through a structure on the forehead
spent most of its life
on land, taking to the called the melon. Echoes of the noises are
seas to hunt.
then transmitted to the whale’s ears via
a fatty pad in its lower jaw. Eocene
whales do not appear to have
had melons though they
Artist’s restoration of Ambulocetus do show evidence of

FIRST WHALES sensitive hearing.
The first known whale, Pakicetus, comes from the
Middle Eocene of Pakistan, a site rich in early whale
fossils. From one of these fossilized skeletons, we now
know that Pakicetus was small – probably less than 6 ft
6 in (2 m) long – and not specialized for life in water.
However, its ear bones possessed features unique to
whales, and its delicate front teeth suggest that it
caught fish, perhaps while paddling in shallow water.
Other early whales were formidable predators –
Ambulocetus looked something like a cross between a The melon sits Any nearby
wolf and a seal and had a long crocodile-like head. Its in a large bony
skull was strong enough to resist the struggles of large depression on the
mammalian prey. top of the skull.

object, such as
another animal,
creates an echo.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

274

EARLY WHALES

Dorudon skull Nostrils were not
located on the forehead
in Eocene whales.

Dorudon and other Eocene whales SKULL EVOLUTION
have two different kinds of teeth. In early whales like Pakicetus, the nostrils were located close
to the tip of the snout, as they are in most land mammals.
More advanced whales like Basilosaurus and Dorudon
have their nostrils located midway along their snouts. In

advanced whales like the Miocene Prosqualodon, the
nostrils are on the top of the head where they
form the blowhole. Whales’ nostrils have
therefore gradually moved backward,
making room for the developing
melon in the forehead.

It is unknown whether
fossil whales had
dorsal fins or not.

Prosqualodon skull Teeth of advanced whales
are all similar in shape.

Unique long body. EOCENE GIANT
Other Eocene whales
were much shorter. Basilosaurus is one of the biggest fossil whales known,
growing to more than 60 ft (20 m). The vertebrae
BASILOSAURUS that make up Basilosaurus’ back and tail
are unusual, elongated bones, unlike the
shortened vertebrae seen in most whales.
These could have made Basilosaurus
more flexible than living whales.
Its huge skull, which can be
more than 3 ft 3 in (1 m)
long, had curved front teeth
and triangular, serrated
cheek teeth. Using these,
Basilosaurus could have
grabbed and sliced
up fish as well
as other marine
mammals.

Scientific name: Basilosaurus Ribs were made
Size: 66–83 ft (20–25 m) long of very thick,
Diet: Other marine mammals, fish heavy bone.
Habitat: Shallow tropical seas
Where found: North America, North Africa, Unlike modern whales, Wear on teeth shows that
South Asia basilosaurs had a Basilosaurus preyed on
Time: Paleogene (Eocene) flexible elbow. large animals.
Related genera: Basiloterus Dorudon

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

275

276

Reference Section

In this section, you can scan a pictorial summary
of life through time, with pauses for dramatic mass
extinctions. Retrace the journeys of prehistoric
creatures, from their deaths millions of years ago to
their stunning resurrection in museum halls. Along
the way, step into the shoes of a paleontologist –
spend time on an exotic dig, then learn what
goes on when fossils reach the laboratory. Watch
scientists reassemble fossil bones and see sculptors
recreate lifelike replicas of ancient animals. Get
tips on conducting your own fossil hunt. Read
about personalities who helped solve puzzles of
the past. Then discover where to see exciting
fossils on display.

277

REFERENCE SECTION

GEOLOGICAL TIME CHART
ROCKS ARE DEPOSITED IN LAYERS, and the layers
such as the Triassic and Jurassic. Periods are
at the bottom of a sequence are the oldest. grouped together to form eras, such as the
The actual ages in years of different rock Mesozoic and Cenozoic. Eras are one of the
layers are worked out by techniques that biggest subdivisions of geological time and
involve measuring the decay of radioactive are separated from one another by major
elements within the rock. Groups of rock extinction events in which important fossil
layers are classified together to form periods, groups disappear from the geological record.

MILLION YEARS AGO PRECAMBRIAN First single-celled and Mawsonites Collenia
multicellular life.
4,600-542

PALEOZOIC ERA

542-488.3 CAMBRIAN PERIOD All major animal Olenellus
groups appear. Orthoceras
488.3-443.7 ORDOVICIAN PERIOD First nautiloids and
jawed vertebrates. Cyrtoceras
First plants and
443.7-416 SILURIAN PERIOD arachnids on land. Baragwanathia Pseudocrinites
First vertebrates with four limbs
416-359.2 DEVONIAN PERIOD and distinct digits. Pteraspis
359.2-299 CARBONIFEROUS
299-251 PERIOD First reptiles and flying insects Sandalodus
PERMIAN PERIOD on land.
Sail-back synapsids Edaphosaurus Diplocaulus
appear on land.

MESOZOIC ERA

251-199.6 TRIASSIC PERIOD First dinosaurs, mammals, Lystrosaurus
turtles, and frogs.
199.6-145.5 JURASSIC PERIOD First birds appear, dinosaurs Pterodactylus
rule the land. Proceratosaurus
145.5-65.5 CRETACEOUS First modern mammals.
PERIOD Non-avian dinosaurs die out. Triceratops

CENOZOIC ERA

65.5-55.8 PALEOGENE PERIOD PALEOCENE EPOCH First owls, shrews, and Taeniolabis Phenacodus
hedgehogs.

55.8-33.9 EOCENE EPOCH First horses, elephants, Palaeochiropteryx Hyracotherium
dogs, and cats.
33.9-23 OLIGOCENE EPOCH First monkeys, deer, Phiomia
23-5.3 MIOCENE EPOCH and rhinoceroses.
5.3-1.81
1.81-0.01 PLIOCENE EPOCH First apes, mice, and many Samotherium
0.01-Present PLEISTOCENE new mammals.
EPOCH
NEOGENE PERIOD HOLOCENE EPOCH First cattle and sheep. Bison Balaena
Whales diversify.

First modern humans Gigantopithecus
appear.

Extinctions caused Homo sapiens
by human activity.

Formation of the Earth PRECAMBRIAN TIME
4,600 MYA

278

FOSSIL TIMELINE

PRECAMBRIAN TIME 4,600-542 MYA

AQUATIC ANIMALS COLLENIA
Stromatolites are layered structures that
THE RISE OF LIFE resemble stony pillars or platforms. They
were widespread in Precambrian times
The first living things were and still exist today in Australia and
prokaryotes – microscopic, elsewhere. These bizarre structures
single-celled bacteria-like were built by colonial microorganisms,
organisms. They evolved in the
Precambrian, probably in the hot such as Collenia, which grew in mats using
water around deep-sea volcanic sunlight for energy. When studied under the
vents. Their fossils first appear microscope, stromatolites can be seen to be made
around 3,500 million years ago. up of fossil prokaryotes and other microorganisms.
Multicellular organisms, or eukaryotes,
arose late in the Precambrian, perhaps Round, flattened
when single-celled forms took to body, with projection
living in colonies. By the end of the at the center
Precambrian, soft-bodied animals were
present. Some of these may be ancestors Body made of
of animals, such as jellyfish and worms, three connected
but others might be bizarre dead ends segments
unrelated to later animals.
EARTH FACTS
EDIACARA
This simple, disk-shaped Precambrian
organism probably lived a static life on the
seafloor, absorbing oxygen directly from the

surrounding water. It formed part of the
Vendian fauna – a group of soft-bodied organisms

first discovered in rocks in southern Australia, and
later found worldwide. Such fossils are highly

controversial because they are difficult to interpret.
Scientists are not even sure if they were animals or plants.

DICKINSONIA NOGORTNHDEWRANNA
This 5-in (13-cm) long SOUTHERN
segmented animal appears GONDWANA
to have lived on or in sandy
parts of the seafloor. The Precambrian represents more
Dickinsonia is known from than 85 percent of geological time
the Vendian faunas of during which the Earth changed
Australia and Russia. Its from a molten ball to a planet
identity is controversial. with continents, oceans, and an
Some experts argue that it atmosphere. The first tectonic plates
was a kind of flat-bodied developed 3,800 million years ago
worm. Others suggest that it and life evolved. Oxygen built up in
was a soft-bodied coral. One the atmosphere much later.
expert has even argued that
Dickinsonia and similar fossils CENOZOIC
were actually lichens. MESOZOIC

This timeline shows each era as
a proportion of all geological time.
The Precambrian era is more than
eight times longer than all the time
elapsed since.

PALEOZOIC

542 MYA 251 MYA 65.5 MYA TODAY

279

REFERENCE SECTION

CAMBRIAN PERIOD METALDETES
AQUATIC ANIMALS The appearance of shells and other hard parts was a

EXPLOSION OF LIFE key event in animal evolution that occurred at the
very end of the Precambrian. Microscopic fossils
Most of the major groups of animals of early shelled animals are found worldwide
that exist today evolved in the Cambrian in Cambrian rocks. They include mollusks
Period. This huge growth in diversity with coiled shells and worms that lived
occurred only in the seas – the land in straight tubes. Archaeocyathans, such
was still bare of life other than as Metaldetes, had porous cone-shaped
micro-organisms – and is called the calcite skeletons. They probably lived
“Cambrian explosion.” Soft-bodied fixed to the seafloor.
animals and stromatolites (bacterial Metaldetes probably
colonies) of the Precambrian were resembled a
largely replaced by species with hard modern sponge.
parts, especially trilobites. Their fossils
have been found in abundance in the Metaldetes taylori
Burgess Shale, a famous fossil-rich Large eyes
area in the Canadian Rocky
Mountains that dates back around
505 million years.

XYSTRIDURA PIKAIA
Trilobites were a tremendously Chordates, the group
successful and varied group of that includes vertebrates,
arthropods, and they make up evolved in the Early
one third of all fossils known Cambrian. A later kind was Pikaia,
from the Cambrian period. a swimming eel-like animal,
Types such as Xystridura had 2 in (5 cm) in length. Pikaia had a
many legs, complex eyes flexible rod called a notochord
made of numerous stiffening its body. In later animals,
individual lenses, and this developed into the backbone.
long antennae. Some Pikaia swam by contracting blocks
burrowing trilobites of muscle around the notochord
from the Cambrian, to produce a wavelike motion.
however, lacked eyes. 280
Other species were
good swimmers,
while others could
roll into balls for
protection.

Each body segment
supported a walking leg
and a gill-bearing leg.

V-shaped muscle blocks
around the notochord

FOSSIL TIMELINE

542–488.3 MYA

WIWAXIA Ridged scale
Perhaps distantly
related to the The head shield supported large
mollusks, Wiwaxia backward-pointing horns.
was 1 in (3 cm) long,
dome shaped, and MARRELLA
covered in scales. It The most common
was equipped with long arthropod in the Burgess
spines, probably for self- Shale is Marella – more than
defense. Wiwaxia is from 25,000 specimens have been
the Burgess Shale, but new collected to date. Up to 1 in
discoveries show that such (2 cm) long, this animal had
animals were widespread a large head shield, and two
in the Cambrian. pairs of long antennae,
although it seems to have
Wiwaxia probably lacked eyes. Its body was
ate algae. made up of 24–26 segments,
each of which carried a two-
branched appendage. The
lower branch was a walking
leg, while the upper branch
carried long gills. The
animal was able to both

walk and swim.
Indentations may
have been sites
of muscle
attachment.

EARTH FACTS

Concave G ONDWANA IAPETUS OCEAN NA
inner surface
indicates an G O N DWA
older
individual. During the Cambrian, most of the
MOBERGELLA world’s landmasses were united as
Among the early the supercontinent Gondwana. This
shelled fossils of the was surrounded by the vast Iapetus
Cambrian are tiny limpetlike Ocean. Smaller landmasses that today
forms, such as Mobergella from form Europe, North America, and
Scandinavia. These might not have Siberia lay in tropical and temperate
been separate, individual animals but zones. There were no ice caps in the
scalelike structures that covered the bodies seas, and water levels were high.
of larger species. Members of another Cambrian
group with hard parts, the halkieriids, were elongate
with scaly bodies. It is possible that Mobergella may have
actually been halkieriid body scales.

281

REFERENCE SECTION

ORDOVICIAN PERIOD

AQUATIC ANIMALS Estonioceras Uncoiled final ESTONIOCERAS
perforatum whorl of shell This swimming mollusc was a nautiloid – a
FILTER FEEDERS group which survives today as the animal
Nautilus. It had a loosely coiled shell and
Another burst of evolution in was adapted for hunting in fairly deep
the Ordovician gave rise to European waters, grabbing prey with its
thousands of new animals. tentacles. Estonioceras was small, just
Many were filter feeders that 4 in (10 cm) across, but straight-
fed on increasing numbers shelled relatives had shells up to 16 ft
of plankton – microscopic (5 m) in length. At the time, these
free-floating organisms – in intelligent Ordovician predators were
the water. These included the largest animals ever to have lived.
mosslike bryozoans, Shell could be
bivalves, and corals, which locked shut by
formed reefs that were home internal pegs and
to swimming molluscs and sockets
other animals. Trilobites
diversified greatly into STROPHOMENA
swimming forms equipped Among the most abundant
with huge eyes and bottom- of Ordovician animals were
feeders with shovel-like brachiopods – filter-feeders whose
snouts for plowing through two shells were joined at a hinge.
mud. The earliest jawed Strophomena was a small
vertebrates – a group that brachiopod that probably lived
includes sharks and bony on sand or mud, although many
fish – probably also appeared of its relatives cemented
in the Ordovician. themselves to submerged rocks.

AQUATIC PLANTS

ALGAE AND LIFE ON LAND MASTOPORA
This reef-forming green alga grew in
Colonial blue-green algae – the stromatolites – which rounded clusters with a characteristic
had evolved in the Precambrian, were still widespread honeycombed surface pattern.
during the Ordovician. True algae, including globular Fossils of the clusters, each about
forms that resembled sponges, lived alongside other 3 in (8 cm) across, are found
reef builders, such as corals, while green worldwide. Limestone
algae, the ancestors of land plants, secreted by the algae covered
colonized freshwater habitats. the surface, protecting
Most significantly, plants Mastopora from hungry
similar to liverworts and herbivores. Superficially
mosses evolved late in resembling a sponge,
the Ordovician and Mastopora was originally
began to colonize thought to be an animal.
the land, which until
this time had been
barren of life. These
plants were still
strongly tied to
water, needing it
for reproduction.

Honeycomb Mastopora favus
pattern on
surface of cluster

282

FOSSIL TIMELINE

488.3–443.7 MYA

Colony about 3 in
(8 cm) long

Serrations on CONODONT
the interlocking Long known only from their small serrated
teeth were used teeth, conodonts were eel-like vertebrates,
to bite and cut or close relatives of vertebrates. With large
up prey. eyes, they probably hunted and ate small
animals. At 16 in (40 cm) in length,
Promissum, an Ordovician conodont from ORTHOGRAPTUS
South Africa, was the largest known Graptolite fossils first appeared in the Cambrian,
conodont. The group has a fossil record but most groups arose in the Ordovician.
that extends from the Late Cambrian to Graptolites formed colonies of interlinked cuplike
the Triassic. structures called thecae, each inhabited by a soft-
bodied filter-feeding animal called a zooid. Some
kinds of graptolites were attached to the seafloor
while others floated in the surface waters.
Orthograptus was a common graptolite whose
colonies consisted of two parallel strips of thecae.

Surface protected
and strengthened by
calcium carbonate

EARTH FACTS

IAP AN
G WANA
ONDWANA ETU S O CE GOND

ACANTHOCHONIA The Gondwanan supercontinent
The surface of Acanthochonia was made up of numerous remained separate from the
diamond-shaped cells arranged in a spiral pattern. All of these landmasses that would become
cells originated from a single central stem, which anchored the North America and Europe, though
alga to rocks or corals. The rounded alga was only about 2 in the Iapetus Ocean had started to
(5 cm) in diameter and lived in coral reefs. close. The Ordovician was a time of
global cooling. Late in the Period a
283 huge ice sheet covered much of the
southern hemisphere.

REFERENCE SECTION

SILURIAN PERIOD

AQUATIC ANIMALS Small body,
about 3 in
NEW LIFE (6 cm) in length

A large-scale extinction event at BIRKENIA Birkenia elegans
the end of the Ordovician greatly
reduced the richness of animal Primitive jawless fish evolved in the Cambrian, but were
life early in the Silurian. However, still thriving well into the Silurian. The small, spindle-
surviving groups – including shaped Birkenia lived in European lakes and rivers. Like
brachiopods, mollusks, trilobites, other jawless fish, it lacked paired fins, making it unstable
and graptolites – soon recovered when swimming. This poor swimmer was unable to catch
and increased in diversity in the fast prey and probably foraged in mud taking in tiny food
warm, shallow continental seas of particles through its vertical slitlike mouth. Its body was
the period. Entirely new aquatic covered by deep, overlapping scales arranged in rows. A
invertebrates, such as primitive sea
urchins, also appeared for the first
time. Jawless fish still thrived while
jawed fish – including armored
placoderms and acanthodians
or “spiny sharks” – diversified,
becoming increasingly important.
The very first land-living animals –
arthropods including millipedes,
centipedes, and scorpions –
evolved from aquatic ancestors
during the Silurian.

row of taller defensive scales grew along the top of its back.

LAND PLANTS COOKSONIA Cooksonia
Best known from hemisphaerica
THE PIONEERS Silurian rocks of southern
Ireland, Cooksonia was the first Branching
The Silurian marks the upright vascular plant. Lacking stems
appearance of the first leaves and roots, it was composed of formed
true land plants, cylindrical stems that branched into two Y-shapes.
making it a critical time in at several points along their length. At PARKA
the evolution of plants. The the ends of the stems were cap-shaped Low-growing, liverwortlike Parka was a land
first land-living plants were spore-bearing structures. Compared to plant, or maybe green alga, from Silurian and
mosses and liverworts that later vascular plants Cooksonia was very Devonian North America and Europe. It had
grew along the edges of small, growing to just 4 in (10 cm) in a flattened, loosely branching shape and was
ponds and streams. Among height, and very simple in shape. It only 2 in (4 cm) or so in diameter. A thick
later Silurian forms were grew along pond and lake margins. protective covering on its outer surface may
the first vascular plants. have helped prevent Parka from drying out,
These contained internal suggesting that it may have grown on land
hollow tubes with a woody rather than in water.
lining, which helped
support the plant and also
carried water around its
body. Because of the
vessels, vascular plants were
able to grow to larger sizes
and farther from water than
mosses and liverworts.

284

FOSSIL TIMELINE

443.7–416 MYA

Each arm was free The paired legs
and could be moved could have been
by strands of muscle. used for walking or
for handling prey.

Abdomen PARACARCINOSOMA
SAGENOCRINITES Sea scorpions were Silurian arthropods –
Crinoids, or sea lilies, were relatives of the spiders. They had long tails and
important animals of the many were equipped with large pincers, which
Silurian seas. Many species they used to grab and dismember their prey.
survive today in deeper waters. Paracarcinosoma was a small sea scorpion, only
Attached to the seafloor by long, about 2 in (5 cm) long. It may have lived in
cylindrical stalks, their tentacled brackish and fresh water as well as in the sea.
heads collect plankton and The squarish head, body, and its six pairs of
suspended food from the sea. limbs were encased in a hard external skeleton.
Sagenocrinites was a small crinoid The last pair of limbs were paddle-shaped and
from Silurian Europe and North would have been used for swimming.
America. Its head and tentacles
were very compact in shape,
suggesting that it lived in
shallower waters that were
constantly churned by waves.

Base of the stem attached
to the seafloor

Stem covered with
short fine leaves

EARTH FACTS

BARAGWANATHIA LAURENTIA
Closely resembling a club
moss, Baragwanathia was a GONDWANA
relatively complex Silurian
Distinct rounded plant. It had branching stems During the Silurian, the southern
spore capsules about 10 in (25 cm) high, which continent Gondwana was fringed by
grew on its grew upward from creeping branches other landmasses. Smaller plate
surface. that spread across the ground. The fragments moved northward and
stems were clothed in short leaves, collided, producing new mountain
Parka decipiens giving the plant a “furry” look. ranges in North America and Europe.
Baragwanathia lived in the Sea levels rose as Ordovician ice
southern hemisphere and melted and the climate became
is known from Devonian warmer and less changeable.
as well as Silurian rocks.

Baragwanathia
longifolia

285

REFERENCE SECTION

DEVONIAN PERIOD
LAND ANIMALS

LIMBS ON LAND Sharp teeth
suggest a diet
The Devonian was one of the most of fish and other
important periods of vertebrate animals.
evolution. The first vertebrates with ACANTHOSTEGA
four limbs and distinct digits evolved Among the earliest of
from lobe-finned fish during this time, four-limbed vertebrates was
and by the Late Devonian they Acanthostega from Greenland. Like its
had spread widely around the world. lobe-finned fish relatives, it was a pond-
Land-dwelling arthropods increased dwelling predator that still had gills and a paddlelike tail.
in number throughout the period. Its limbs suggest that it would not have been good at walking
Primitive, wingless insects and even on land. However, fossilized tracks show that some four-
winged forms arose while spiders and footed vertebrates had ventured onto land by this time.
their relatives became more diverse.

AQUATIC ANIMALS Pointed fins with a
prominent central
DEVONIAN DIVERSITY row of bones.
DIPTERUS
Heavily armored jawless fish Lungfish such
flourished in the Devonian seas as Dipterus were
and jawed fish were by now also one of the most
abundant. Among the bony fish, abundant groups of the Devonian.
lobe-finned fish were numerous Five species of these lobe-finned fish
and diverse while ray-finned fish survive in modern times. Dipterus swam in
began to become more important. European waters and, like all lungfish, had large
Several groups of trilobites were crushing teeth. Fossilized stomach contents
still widespread and ammonoids show that it was preyed on by placoderms.
and modern-type horseshoe crabs
appeared. Their descendants
survive to this day.

LAND PLANTS ARCHAEOPTERIS
This widespread and highly successful
LEAVES AND ROOTS Late Devonian plant was one of the
first to resemble modern trees. It had
The Devonian Period saw the an extensive root system and its
most important steps so far in the trunk had branches with reinforced
development of land plants. Leaves joints at its crown. Archaeopteris was
and roots evolved independently in also one of the first plants to reach
a number of different groups. For great size, reaching about 65 ft (20
the first time, plants displayed m). Scientists once thought that its
secondary growth – their stems woody trunk belonged to a different
could not only grow in length, species and named it Callixylon.
but also in diameter. These
developments allowed plants to Branching, Archaeopteris
grow far larger than before. The fernlike leaves
early reedlike pioneers on land
gave way to gigantic trees and
species with complex leaves.
Horsetails, seed ferns, and
conifer ancestors appeared
late in the Devonian, and it was
these forms that would evolve
into species that later made up the
lush forests of the Carboniferous.

286

FOSSIL TIMELINE

416–359.2 MYA

Seven toes ICHTHYOSTEGA FOSSIL
on each foot Ichthyostega was an early four-footed
vertebrate. It probably hunted fish and
Ichthyostega other prey in shallow pools. Features of its
Limbs served limbs suggest that it was relatively advanced
as props for and was related to the ancestor of all later
walking on land. four-footed vertebrates. Ichthyostega had a short,
broad skull and very broad ribs, which helped
support its body when it crawled on land.
Large eye for
excellent vision

EASTMANOSTEUS PHACOPS Phacops
Placoderms were jawed fish that This small
were abundant in Devonian seas. trilobite lived in
They included predators, armored warm, shallow seas.
bottom-dwellers, and flattened ray- Like many arthropods,
like forms. Some Late Devonian each of its body segments
placoderms reached 33 ft (10 m) supported two sets of limbs.
in length, making them the For protection against predators
largest vertebrates yet to evolve. it could roll up its body and tuck its
Eastmanosteus, known from tail beneath its head. Seven of the
Australia, North America, eight groups of trilobites, including
and Europe, was less than the one to which Phacops belonged,
6 ft 6 in (2 m) long but died out at the end of the Devonian.
would still have been
a formidable hunter.

EARTH FACTS

ZOSTEROPHYLLUM Clusters of EURAMERICA
Lacking roots and leaves, spore-bearing
Zosterophyllum was a primitive land plant. Its stems GONDWANA
erect, branching stems grew not from roots, Zosterophyllum
but from a complex underground rhizome llanoveranum The Devonian world was warm and
(stem). The sides of the stems carried small mild. The huge continent Gondwana
kidney-shaped capsules in which spores 287 lay over the South Pole while modern
were produced. Reaching a height of Europe and North America were
around 10 in (25 cm), the plant probably positioned close to the equator. Sea
grew along the swampy edges of lakes. levels were high, and much of the
land lay under shallow waters, where
tropical reefs flourished. Deep ocean
covered the rest of the planet.

REFERENCE SECTION

CARBONIFEROUS PERIOD

LAND ANIMALS

ORIGIN OF THE AMNIOTES WESTLOTHIANA Sharp teeth
Primitive four-footed vertebrates are well suggest
Amniotes, vertebrates whose embryos known from fossils in North America and a diet of
are enclosed by a watertight membrane, Europe. Westlothiana was discovered in insects.
evolved in the Carboniferous. Both major Scotland, in rocks formed in a lake fed by
amniote groups – reptiles and the mammal- hot, volcanic springs. Its fossils were found
like synapsids – appeared at the time, while alongside those of four-legged and
other more primitive land-living vertebrates snake-like tetrapods as well as
diversified. At 10 ft (3 m) in length, the millipedes, scorpions, and
synapsid Ophiacodon was one of the biggest spiders. Westlothiana was about
known land animals of the time. Flying 12 in (30 cm) long. Its long
insects evolved and together with arachnids body was carried on short legs.
– spiders, scorpions, and mites – increased
in size and diversity. Westlothiana
lizziae

AQUATIC ANIMALS

DIVERSE DEPTHS SYMMORIUM Internal rodlike structures called
Many of the Carboniferous sharks ceratotrichia supported the fins.
Sharks and bony fish were bizarre compared to modern
dominated Carboniferous forms. Some were decorated with
seas, but ray-finned fish, peculiar spiky crests and spines.
the actinopterygians, also Stethacanthus had a spine on its
diversified greatly during this back covered with toothlike
period. Trilobites were still material, while Symmorium
present, but survived as only looked similar but lacked
a handful of groups. Crinoids, the spine. Some
brachiopods, echinoderms, scientists think that
and swimming mollusks it was the female
inhabited the tropical of Stethacanthus.
coral reefs of the time.

LAND PLANTS Pointed teeth Fossilized
show that tubers and
FORESTS AND FLOODPLAINS Symmorium roots of
was a predator. Equisetites
Lush tropical forests forming vast
swamps and forested deltas were EQUISETITES
widespread in the Carboniferous. Equisetites is an extinct
Clubmosses and horsetails were horsetail, which came from
important components of these a group that survives today
forests, and some grew to immense in the form of Equisetum.
sizes. Lepidodendron was a clubmoss It grew to a height of
130 ft (40 m) tall, while Calamites around 20 in (50 cm) from
was a 50-ft (15-m) horsetail. underground stems (tubers),
Gymnosperms – the group of and its straight stem carried
plants with naked seeds that leaves arranged in regular rings
includes conifers and cycads – or whorls. Equisetites dominated the river
began to diversify during the banks and lake edges of the Carboniferous,
Carboniferous. Toward the end of and these habitats are still favored today
the period, the huge European and by modern forms of Equisetum.
North American floodplains began
to shrink as the climate became
less wet. The clubmosses were
then replaced by ferns and
seed ferns from drier habitats.

288

FOSSIL TIMELINE

Two eyes on a 359.2–299 MYA
projecting bump

GRAEOPHONUS
Arachnids, the arthropod group that includes spiders,
scorpions, and their relatives, are well represented in
the Carboniferous fossil record and many new kinds
made their first appearance at this time. Graeophonus was
an early member of a group that survives to this day – the
whip scorpions. These have six walking legs and a front
pair of serrated pincers that they use to grab prey. They
lack poisonous fangs, but have sharp jaws.
Growth lines,
or sutures,
on shell

Skeleton made Forked tail
of cartilage suggests fast
swimming
speeds. GONIATITES
This animal is a type
of swimming mollusk
with a coiled shell. It was a
member of a group of ammonoids
(ammonitelike animals) that was
dominant throughout the Paleozoic.
Like all ammonoids, Goniatites had gas-
filled shell chambers that allowed it to
float. It probably had complex eyes and
beaklike mouthparts. Goniatites lived in
large swarms over reefs in shallow seas.

Straplike leaves EARTH FACTS

CORDAITES Cordaites EURAMERICA
This coniferlike angulostriatus G O N D WA N A
land plant grew
in Carboniferous 289 The Carboniferous is known as the
mangrove swamps, “Age of Coal” because decaying
but died out in vegetation from the vast forests was
the Permian. It had transformed into coal. The main
characteristic long, leathery landmasses present were the two
leaves and its straight main trunk grew to a height huge continents of Gondwana and
of up to 100 ft (30 m), although other species of Euramerica. Oxygen levels were high,
Cordaites were shrublike. It produced seeds in loose and this may have allowed giant
cones. The leaves, stems, and seeds of Cordaites had terrestrial arthropods to evolve.
been given different names because they were
originally thought to belong to different species.

REFERENCE SECTION

PERMIAN PERIOD

LAND ANIMALS Fragment of EDAPHOSAURUS
palate with teeth This Permian synapsid had
SYNAPSIDS a broad, rounded body with

The most important and diverse a tall fin on the back. This
land-dwelling vertebrates of fin was richly supplied with
the Permian were the primitive blood vessels and so could
synapsids – early members absorb or radiate heat. It
of the group that includes
mammals. Most were small or may have been used to control
medium-sized animals equipped the animal’s body temperature.
with powerful skulls and sharp Edaphosaurus had two types of
teeth to deal with a diet of flesh teeth. Peglike teeth lined its jaws
or insects. They thrived, along and crushing teeth were located
with reptiles and arthropods, on its palate. These features
including spiders and insects. suggest that it was a herbivore
that fed on ferns and other
AQUATIC ANIMALS tough Permian plants.
DERBYIA
SEAS OF LIFE Brachiopods were shelled, filter-feeding
animals that evolved in the Cambrian
Immense reefs, mostly built by and still survive today as lamp shells.
bryozoans (tiny, colonial animals) Their larvae could swim, but
and sponges, teemed with marine life adults lived a static life on the
in Permian times. Shelled animals sea floor. Derbyia was a large,
called brachiopods burgeoned, heavy brachiopod that grew
important new fish groups evolved, to 3 in (8 cm) in diameter
and some reptiles – the mesosaurs in the Carboniferous and
– returned to live in water. The Permian seas. Brachiopods
Permian ended with the biggest were plentiful in the Devonian,
mass extinction of all time. Many but there were few left by
animals died out, although some, the end of the Permian.
such as fish, were not badly affected. Sword-shaped
leaves
LAND PLANTS
Glossopteris
NAKED SEEDS
Apart from lacking flowering plants, Permian plant
communities resembled some that thrive today. The
clubmosses and horsetails that had formed the vast
Carboniferous forests largely disappeared and were
replaced by gymnosperms, plants that produce their
seed “naked,” not enclosed
in a fruit. Conifers
(gymnosperms with GLOSSOPTERIS
needlelike leaves) One of the most
flourished and two other important Permian
gymnosperm groups – gymnosperms was
Glossopteris. This tree,
which grew to 26 ft
cycads and ginkgos – also (8 m), and its close
evolved. Late in the relatives dominated
Permian, many of the the southern part of the
conifers developed thick supercontinent Pangea.
fleshy leaves protected by Fossils of Glossopteris have an
important place in scientific
hairs. These features helped history. They were found across all the
the plants to tolerate the southern continents, thereby providing
hot and dry climate that one of the first pieces of evidence to
typified Late Permian times. support the theory of continental drift.

290

FOSSIL TIMELINE

Eye socket 299–251 MYA

Dimetrodon loomisi skull DIMETRODON
A stout skull and large, pointed
teeth made Dimetrodon an
awesome predator. This fin-
backed synapsid grew to
around 10 ft (3 m) in
length. It had lightly built
limbs so could run fast
to catch its prey. Animals
like Dimetrodon were
important because they
gave rise to an entirely
new group of synapsids,
the therapsids, which became
dominant in the late Permian.

PALEONISCUM Long, streamlined body Asymmetric
Ray-finned fish, which evolved in suited to fast swimming tail fin
the Devonian, continued to diversify
during the Permian, and a major
new group – the neopterygians –
appeared. Paleoniscum was a primitive
ray-finned fish distantly related to
the neopterygians. It grew to around
8 in (20 cm) in length. Covered
by a coat of overlapping scales,
this spindle-shaped predator
was a strong swimmer.

Paleoniscum magnus

Small, pointed MARIOPTERIS EARTH FACTS
leaflets Found in late
Carboniferous and PANG EA
early Permian swamps,
Mariopteris grew to a The two major landmasses of the
height of around 16 ft early Permian – Euramerica in the
(5 m). Its stem consisted north and Gondwana in the south –
partly of old leaf bases. collided late in the period to form
Some species were the supercontinent Pangea. The
treelike, while others Pangean climate became hotter
were climbing plants. and drier. While the south seems
to have been relatively cool, tropical
Mariopteris maricata conditions prevailed in the north.

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PERMIAN EXTINCTION
THE END OF THE PERMIAN PERIOD, 251 million years ago, saw
the greatest mass extinction of all time, a period of crisis
that has been called “the time of great dying.” Perhaps as
few as five percent of all species survived. In the seas, reef-
dwelling animals were severely affected and trilobites, sea
scorpions, and key coral groups disappeared. On land,
many synapsid and reptile groups vanished. Some
experts think that the Permian extinction happened
quickly, but it seems unlikely that a single catastrophe
was responsible. It is more probable that a series of
several events gradually resulted in the mass extinction.
The formation of the supercontinent Pangea, for example,
would have destroyed important shallow coastal seas and
coastline habitats. Climate changes and volcanic eruptions
undoubtedly contributed to the extinction. FIERY END
A possible cause of the end-Permian
extinction is volcanic activity. Huge
eruptions of volcanic material are known
to have happened in Siberia at this time.
Around one million cubic miles of lava
poured out, covering enormous areas of
the land surface, and pumping vast
amounts of gases and dust into the air.
This volcanic dust blocked the Sun’s rays,
causing the air to chill. Then, later, as dust
settled, carbon dioxide trapped so much of
the Sun’s heat that temperatures soared
with lethal effects.

CLIMATIC CRISIS Branching colonies
Climate change characterized the end of the Permian. Rocks from the of bryozoans, or
period indicate that cooling occurred in some areas and ice sheets built moss animals
up at the poles, causing the global sea level to drop. The white ice
sheets reflected sunlight back into space, lowering global temperatures Rugose corals
even further. Falling sea levels may have exposed huge areas of coal on completely
the seafloor. This would have released large amounts of carbon dioxide disappeared
into the atmosphere, so reducing oxygen content. Less oxygen in the in the Permian
atmosphere may have contributed to the extinction of animals with extinction.
active lifestyles, such as the mammal-like synapsids. Brachiopods like
Edriostege, grew
DESERT DEVASTATION on the tops of
When the Permian landmasses the reefs.
collided, they produced the vast
continent of Pangea. Rains
and mists that arose at sea
could no longer reach the
interior of the land, with the
result that some parts of the
Permian world became drier
and hotter. Deserts grew ever
larger, and animals not adapted
for life in the arid conditions

became extinct.

Cambrian 542–488.3 Ordovician 488.3–443.7 Silurian 443.7–416 Devonian 416–359.2 Carboniferous 359.2–299 Permian

PALEOZOIC 542–251 MYA

292

FOSSIL TIMELINE

DEATH OF A REEF The huge
tubular sponge
A Permian coral reef is shown healthy Heliospongia
on the left-hand side of the image – and was one of the
dying as it would have appeared during largest reef
the Permian extinction – on the right- organisms of
hand side. Permian reefs – complex the Permian.
environments built by corals and
sponges – were inhabited by thousands Reef animals
of different animals and plants. Lowered would have died
sea levels and reduced areas of shallow off as oxygen
seafloor that resulted from the formation levels in the sea
of Pangea destroyed the areas in which dropped.
reefs could grow. The reefs were
gradually killed off, causing an Gastropods
enormous drop in the diversity grazed on algae
of marine life. Reduced quantities that grew on
of oxygen in the Permian atmosphere the reefs.
would also have meant that sea water
contained less oxygen than before.
Entire oceans would have slowly
become stagnant, suffocating the
life they contained.

299–251 Triassic 251–199.6 Jurassic 199.6–145.5 Cretaceous 145.5–65.5 Paleogene 65.5–23 Neogene 23–present
MESOZOIC 251–65.5 MYA
CENOZOIC 65.5 MYA–present

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TRIASSIC PERIOD

LAND ANIMALS CYNOGNATHUS
This aggressive Early Triassic
THE AGE OF REPTILES predator was a member of the
cynodonts – a group of advanced
The Triassic was the start of the synapsids. Growing to 6 ft 6 in
“Age of Reptiles” and a time when (2 m) in length, it possessed
animals from very different lineages prominent canine teeth, shearing
lived alongside one another. Synapsid cheek teeth, and large jaw muscles
relatives of the mammals, were still that allowed it to hunt other large
important but were gradually being synapsids. It may have been warm-
driven to extinction. Archosaurs, the blooded and fur-covered like a
“ruling reptiles,” became important and mammal, and its close relatives
the first crocodylomorphs, pterosaurs, were themselves the ancestors
and dinosaurs all arose late in the of mammals.
Triassic. The first turtles, frogs, and
mammal-like animals also appeared.

AQUATIC ANIMALS Diamond-shaped DICELLOPYGE
scales covered the Primitive ray-finned fish like
SEA CHANGE streamlined body. Dicellopyge were important
predators in the Triassic. This
Modern-type corals formed small freshwater fish from southern
the Triassic reefs and new Africa had a deeply notched tail
groups of ammonoid suggesting that it was a fast swimmer.
molluscs appeared. Its deep skull and jaws were armed
Advanced ray-finned fish with conical teeth that allowed it to
and the first modern sharks catch and eat smaller fish and
and rays replaced slower, swimming invertebrates.
older kinds of marine life.
Primitive ichthyosaurs evolved
and soon became dolphin-
shaped predators. Some were
as big as modern whales.

LAND PLANTS

DOMINANT CONIFERS Leaf fossilized
in mudstone
Most plants of the earlier Ginkgo
Paleozoic Era reproduced by biloba
spores and so relied on moist leaf
habitats to reproduce. These
groups – including the famous GINKGO
glossopterids of the southern This tree, which evolved in the
continents – suffered in the Triassic, survives essentially unchanged
drier conditions of the Triassic, to this day. A native of China, it has
when the landscape was been transported around the world for
increasingly dominated by planting in urban parks and gardens,
evergreen trees (conifers and partly because it grows well in heavily
other gymnosperms). Among polluted air. Ginkgo grows to around 115 ft
the more modern kinds of (35 m) in height. It is deciduous, and there
plants, cycads became well are abundant fossils of its leaves. Members
established. Ginkgos – relatives of the Ginkgo genus typically grew in damp
of the conifers – became more habitats in temperate climates.
successful and at least seven
genera, including the modern
genus Ginkgo, lived during
Triassic times.

294

Enlarged, stabbing FOSSIL TIMELINE
canine teeth
251–199.6 MYA

MEGAZOSTRODON
One of the earliest of all
mammaliaforms, Megazostrodon, was
only about 5 in (12 cm) long and
lived in Africa, although similar
forms inhabited Europe and Asia.
Like other early mammals, it was
probably nocturnal and
resembled a modern shrew in
appearance and lifestyle. Its teeth
and jawbones suggest that it
hunted insects and other small
animals and hid in burrows. As in
later mammals, some of its

jawbones formed
parts of its ear.

Deep jaws could Small,
hold struggling prey. delicate
bones

Limbs were NEUSTICOSAURUS
used as The sauropterygians were a group of marine reptiles
paddles that evolved during the Triassic. The most famous
when in members of the group were the plesiosaurs.
the water. Neusticosaurus was a small, amphibious, predatory
sauropterygian that lived in the shallow seas of Triassic
Europe,. where it hunted invertebrates and fish. Fossils
of babies preserved without eggshells suggest that these
reptiles may have given birth to live young.

Thick, heavy ribs helped keep EARTH FACTS
Neusticosaurus submerged.

PACHYPTERIS TETHYS
Seed ferns (pteridosperms), OCEAN
such as Pachypteris, were not
ferns at all, but primitive PANGEA
seed plants that lived in
swampy areas. They had Typical height The vast supercontinent of Pangea
woody stems studded 6 ft 6 in (2 m) straddled the equator during the
with dried-out leaf bases. Triassic. Hints that it would later split
Their tops had fernlike 295 up came from the narrow seaway that
fronds that carried the separated North America from
seeds. The group was Europe and another tongue of sea,
very successful late in the Tethys, which encroached on
the Paleozoic, but gradually Europe. The climate was generally
declined in importance during the warm and dry.
Mesozoic, finally becoming extinct
in the Cretaceous. Pachypteris, which grew
worldwide in tropical forests, was one of the
last seed ferns to die out in the Cretaceous.

REFERENCE SECTION

JURASSIC PERIOD

LAND ANIMALS PTERODACTYLUS
Pterosaurs were reptiles that
RULE OF THE DINOSAURS developed wings and powered
flight. They evolved in the Triassic
Life on land took on a very different and diversified during the Jurassic,
appearance in the Jurassic. Most when shorter-tailed, longer-winged
crocodile-group archosaurs and forms appeared. Pterodactylus was a
synapsids were wiped out at the small Jurassic pterosaur that lived
end of the Triassic (but some small along shorelines, feeding on fish and
synapsids, including early mammals, crustaceans. Just 12 in (30 cm) long, it
survived). Giant dinosaurs took over as had a lightly built skeleton and thin,
the dominant animals. On land, plated hollow bones. Its wing membrane was
stegosaurs and long-necked sauropods were supported by the long fourth finger.
preyed upon by large theropods. In the air,
new kinds of pterosaurs were seen and the first This specimen preserves its wing
birds evolved from small predatory dinosaurs. membranes, throat pouch, and foot webbing.

AQUATIC ANIMALS Slender clawed toes

JURASSIC DIVERSITY ICHTHYOSAURUS
Advanced ichthyosaurs (“fish lizards”), swimming crocodylomorphs, and
Important marine animals that appeared in new kinds of plesiosaurs all added to the diversity of marine reptiles in
the Jurassic include ammonites, belemnites, the Jurassic. Ichthyosaurus was a European fish lizard. It had large, sensitive
and modern-type sharks and rays. Teleosts –
bony fish – diversified greatly into long- eyes and a slim snout containing many cone-shaped teeth, both
bodied predatory forms as well as gigantic of which helped it catch fish and swimming mollusks. There
filter-feeders, which may have been the were several species of Ichthyosaurus ranging in size
biggest fish of all time. Crinoids, from 3–10 ft (1–3 m) long.
relatives of today’s sea lilies, were
important during the period.
Giant forms, some with stalks as
long as 50 ft (15 m), grew from
floating driftwood.

LAND PLANTS

THE AGE OF CYCADS Ring of bony plates Nostril was
located close to
Cycads, conifers, and ginkgos were Cycas fronds the eye socket.
important Jurassic plant made of many
groups. So many cycads parallel leaflets CYCAS
grew in the forests of the Cycads are gymnosperms that reached
time that the Jurassic is their greatest diversity and abundance
often called “the Age of during the Jurassic. Cycas, of which
Cycads.” One group of
cycadlike plants – the about forty species survive today, first
bennettitaleans – were appeared in the Jurassic. Some
significant because they may species grew into giant tree-
have been the ancestors of flowering like forms, while others were
plants. Jurassic conifers included smaller and more fernlike.
close relatives of living pines, yews, Jurassic cycads lived
redwoods, and cypresses. Ferns worldwide, but today’s
formed much of the ground cover, species are restricted to
and all three major fern groups had the tropical and
probably evolved by the Jurassic. Club subtropical zones.
mosses, horsetails, and seed ferns
continued to survive but were not Many cycad
as important as in earlier times. leaves were
poisonous.

296

Serrated teeth in FOSSIL TIMELINE
lightly built skull
196.6–145.5 MYA

Long hind limbs COMPSOGNATHUS ARCHAEOPTERYX
with four toes The chicken-sized Perhaps the first true bird,
Compsognathus was an Archaeopteryx evolved in the
advanced predatory dinosaur Jurassic from small theropod
from Late Jurassic Europe. ancestors. It retains many
It walked on its two long, slim features of its reptile past –
hind limbs and probably stalked three working fingers, true
its prey of small lizards teeth, and a breastbone
and insects. It was similar without a keel. This famous
fossil – known as the Berlin
in size, habit, and specimen – was discovered
distribution to the bird in the Solnhofen limestones
Archaeopteryx, and the of Germany in 1877.
two may have lived side- Remarkably, it preserves
by-side in the woodlands complete impressions of the
of southern Germany. wing and tail feathers.

ASPIDORHYNCHUS Triangular skull
Among the new Jurassic teleosts were long- with forward-
facing eyes
bodied predators, such as Aspidorhynchus.
Growing to around 20 in (50 cm) in length, it

had a pointed skull, large eyes, and sharp
teeth. Its upper jaw was extended beyond the

lower jaw, forming a prominent toothless
“beak.” Its tail was symmetrical, and thick

rectangular scales protected its body.
Aspidorhynchus was widely distributed in

shallow, subtropical seas.

EARTH FACTS

WILLIAMSONIA TETHYSPAN
This plant, which lived OCEAN
Flowers probably throughout the GEA
pollinated by insects Mesozoic, was a member
of the Bennettitales – a The Pangean supercontinent split as
group that may include the Atlantic opened up between the
the ancestors of flowering areas that today form Africa and
plants. It had a robust stem North America. The land that would
that was covered in diamond- later become Antarctica, India, and
shaped scales and grew large Australia started to move away from
flowerlike structures. The the rest of Pangea. The climate was
Bennettitales had leaves that warm, and, with no polar ice caps, sea
resembled those of cycads, levels were high worldwide.
and were probably related
to this group.

Williamsonia

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CRETACEOUS PERIOD

LAND ANIMALS Zalambdalestes Stiff tail helped balance
probably fed the heavy body.
NEW DINOSAURS on insects

Dinosaurs remained the dominant land ZALAMBDALESTES
animals during the Cretaceous. New Early Cretaceous mammals were small and
groups, including tyrannosaurs, duck- insignificant, just as they had been throughout
billed hadrosaurs, and horned the Triassic and Jurassic, but an important new
dinosaurs, spread across the northern group emerged later in the Period. Characterized by
continents, while birds evolved from three-cusped teeth, this group included Zalambdalestes,
toothed Archaeopteryx-like species into which probably resembled a modern elephant shrew.
forms that resembled modern kinds.
Snakes developed from lizard ancestors
and new groups of insects, including
moths, ants, and bees, appeared feeding
on and pollinating the newly evolved
flowering plants.

AQUATIC ANIMALS

MESOZOIC MARINE REVOLUTION MACROPOMA Mobile skull
Coelacanths – fleshy-finned fish that first appeared joint
Marine invertebrates took on a distinctly in the Devonian – grew to sizes of up to 10 ft (3 m) in allowed
modern look during the Cretaceous. Crabs Cretaceous seas, though the group was in decline later in jaws to
and other modern crustaceans appeared, the Period. Macropoma was a European coelacanth, less open wide
as did predatory gastropod mollusks and than 24 in (60 cm) long. It had a short, deep body and
burrowing sea urchins. Among fish, the large fins that would have aided maneuverability. Its tail
teleosts (advanced bony fish) underwent a had three lobes – a feature common to all coelacanths.
massive increase in diversity and relatives of
modern herrings, eels, carps, and perches
all appeared. Swimming lizards called
mosasaurs and the first marine turtles
and aquatic birds also evolved.

LAND PLANTS

FLOWER POWER BETULITES
Betulites is an extinct member of the birch family, and a close
Cretaceous forests were largely
dominated by several groups of relative of Betula, the familiar modern birch tree. Like
gymnosperms, particularly living birches, it grew in temperate climates,
conifers, including cypresses, favoring lakesides and other damp
bald cypresses, and monkey- habitats. Betulites had round or oval
puzzle trees. Other leaves that had teeth along their
gymnosperm groups, such as margins – typical of plants that grow
cycads and ginkgos, declined in cool or dry environments.
in importance. Flowering Because fossilized Betulites leaves
plants – the angiosperms – are frequently detached from
arose, first as small, weedlike twigs, this tree was probably
forms in areas of land deciduous.
disturbed and trampled by
herds of dinosaurs. Later in the Leaf fossil
period, flowering plants, in ironstone
including birches, willows, nodule
and magnolias, formed forests
in which the dinosaurs lived, Betulites
but ferns remained important
wherever rainfall was high.

298