MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 51 ded. Gasparini (1985) reviewed the Jurassic marine reptiles of South America, listing the finds until then reported in northern Chile. At that date, all findings of plesiosaurs in northern Chile corresponded to indeterminate forms within the group. Subsequently, the first determinations of possible family-level clades were proposed for remains from the Upper Jurassic of Cerritos Bayos, west of Calama. Otero and Soto Acuña (2010) suggested the eventual presence of cryptoclidid plesiosaurs based on very fragmentary material. These remains were subsequently reevaluated, being later referred to Cryptoclididae (Otero et al., 2015a) and subsequently complemented with new, more informative specimens (Otero et al., 2020b). Additionally, during 2017, associated and apparently articulated remains of a large marine reptile were found. Its excavation was interrupted due to the COVID-19 pandemic in 2019, however, the remains exhumed until then allowed us to recognize their correspondence to a still indeterminate Pliosauridae (Otero et al., 2020a). 3. LOCALITIES AND GEOLOGICAL SETTING Six geological units have provided remains of Jurassic plesiosaurs in Chile. All of them are located in the northern part of the country. These units are listed below, indicating their age, environment and taxonomic determination for the plesiosaur remains found (numbering is also consistent with the map of Fig. 2). 1) Los Molles Formation (Cecioni and Westerman, 1968)― Unit of Coastal marine transitional environment, constrained to the Anisian-Pliensbachian on the basis of cephalopods and flora (Cecioni and Westermann, 1968). In this unit, the presence of presumed gastralia of plesiosaurs was reported (Casamiquela, 1973). 2) El Profeta Formation (Chong, 1973)―Continuous sequence, of marine character, with abundant fossil content that allows constraining its age to the Triassic-Kimmeridgian. The plesiosaur remains in this unit come from Sinemurian levels (Lower Jurassic). 3) Lower Caracoles Group (sensu Tomlinson et al., 2001)―
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 52 Marine levels exposed in the Ojo Opache sector, West of Calama, with cephalopod fauna that allows the unit to be restricted to the Aalenian-Bajocian. These levels have provided remains referable to Rhomaleosauridae plesiosaurs and new material still under study. 4) Lautaro Formation (Segerstrom, 1959)—Carbonate marine sequence exposed in the eastern part of the Región de Atacama as NNE-NS stripes. The plesiosaur remains known in this unit come from the Quebrada de la Iglesia Member (upper member), comprised by red carbonate sandstones, and restricted to the middle Toarcian-upper Bajocian based on their fossil content (Salazar et al., 2013). 5) Quehuita Formation (Vergara, 1978)―Marine sedimentary succession in overlying contact with Paleozoic and Triassic rocks, and underlying Cenozoic continental sedimentary sequences. Its abundant fossil fauna, and especially the presence of ammonoids, allowed constraining it to the lower Callovian. The plesiosaur remains known in this unit come from Sierra del Medio, Antofagasta Region. 6) Cerro Campamento Formation (Lira, 1989; emend. Duhart et al., 2018)—It comprises a well-stratified marine sedimentary succession, regressive in nature towards its roof, with the presence of evaporites in its youngest levels. Its abundant fossil content allows constraining it to the Bathonian?-Kimmeridgian (Biese, 1960; Duhart et al., 2018). Remains of plesiosaurs have been found in Callovian and Oxfordian levels of this unit. Remains of Pliosauridae and Cryptoclididae have been recovered in this unit.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 53 Figure 2: Distribution of plesiosaur finds in northern Chile.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 54 4. MATERIALS Part of the historical records were revised from their original illustrations, since their repository was not clarified in their first publications. Likewise, for some of these materials their current whereabouts are unknown, making a direct re-evaluation impossible. On the other hand, some materials from Sierra Moreno (Región de Antofagasta) were directly observed, while those materials from Cerritos Bayos (Región de Antofagasta) were directly inspected in detail, or even prepared for study. The materials reviewed here and their condition for this work are listed in Table 1. The locations of the findings reviewed here are illustrated in Fig. 2. Institutional Abbreviations—MUHNCAL, Museum of Natural and Cultural History of the Atacama Desert, Calama, Chile. SGO.PV., Paleontology Area, National Museum of Natural History, Santiago, Chile. NHMUK, Natural History Museum, London, UK. Institutional Permits—The collection of recent material was done under authorization from the National Monuments Council (Consejo de Monumentos Nacionales, Chile), through Ord. CMN No. 1464/2018.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 55 First taxonomical referral Original reference Updated taxonomical referral Anatomical elements stage horizon locality Remarks Teleosaurus neogaeus Burmeister and Giebel (1861) Burmeister and Giebel (1861) Plesiosauroidea indet. a single dorsal vertebra Bajocian Lautaro Formation Cerro Blanco, SW Lautaro dam, Región de Atacama Originally referred to as a crocodile, and later reassessed as a plesiosaur (‘Plesiosaurus neogaeus’ von Huene; nomen dubium). Repository unknown. ‘Plesiosaurus neogaeus’ von Huene (1927) Plesiosauria indet. a dorsal vertebra likely Bajocian Lautaro Formation Cerro Blanco, SW Lautaro dam, Región de Atacama reassessment of the vertebra previously described by Burmeister and Giebel (1861) Plesiosaurus Biese (1957; 1961) ? ? lower Callovian; Oxfordian Cerro Campamento Formation Calama, Región de Antofagasta Material never figured, repository unknown Plesiosauria indet. Casamiquela (1973) ? presunt gastralia Upper Triassic not provided. Likely, it belongs to Los Molles Formation Los Molles, Región de Valparaíso plesiosaur Chong and Gasparini (1976) Plesiosauria indet. remains of a limb Sinemurian not provided Cerro Campamento, south of Escondida Mine, Región de Antofagasta Material identified by R. Casamiquela, but never figured probable plesiosaurs Chong and Gasparini (1976) Plesiosauria indet. teeth and other fragments Callovian not provided Sierra de Moreno, Región de Antofagasta Material never figured probable plesiosaurs Gasparini and Chong (1977) aff. Pliosauridae a large coracoid fragment and a dorsal centrum lower Callovian Quehuita Formation Sierra del Medio, Región de Antofagasta material in exhibition at Museo Ruinas de Huanchaca (pers. Obs. 2022) Ichthyosaurus leucopetraeus, Ichthyosaurus posthumus Tavera (1981) Plesiosauroidea indet. middle Bajocian Lautaro Formation among the material, few plesiosaur remains were included in the description, being confused with ichthyosaur remains. Most of the material was lost, except by a single vertebra, reassessed by Otero et al. (2020b). Plesiosauria Gasparini (1985) Plesiosauria indet. Lower to Upper Jurassic several units several localities from northern Chile Gasparini (1985) listed all the historical reports of plesiosaurs from northern Chile Muraenosaurus sp.; Vinialesaurus sp. Otero et al. (2020c) a vertebral series, a postcranial skeleton and a jaw lower and middle Oxfordian Cerro Campamento Formation Calama, Región de Antofagasta Pliosauridae indet. Otero et al. (2020a) a fragmentary jaw, and two propodials of the same individual lower Oxfordian Cerro Campamento Formation Calama, Región de Antofagasta aff. Rhomaleosauridae Otero et al. (2020b) Rhomaleosauridae indet. a radius, gastralia, pelvic elements and 10 caudal centra Aalenian-Bajocian lower Caracoles Group Ojo Opache, Calama, Región de Antofagasta reassessed in this study with the first description of its radius Table 1: List of the reports regarding plesiosaurs found in northern Chile, including remarks on the previous mentions of the material and their advances, on each case.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 56 5. SYSTEMATIC PALEONTOLOGY Plesiosauria de Blainville, 1835 Plesiosauria indet. (Fig. 3A-D) Teleosaurus neogaeus Burmeister and Giebel, 1861; nomen dubium. Plesiosaurus neogaeus (von Huene, 1927); nomen dubium. Material―Remains illustrated by Burmeister and Giebel (1861: tafel I), corresponding to a complete dorsal vertebra and remains of a rib. Location and Horizon―Cerro Blanco, 10 km southwest of Tranque Lautaro, Atacama Region. Lautaro Formation, Middle Bajocian. Remarks―Observations based on the illustration provided by Burmeister and Giebel (1861: Tafel I) allow recognizing that both the center and its respective transverse process are well fused, with a diffuse or inconspicuous suture line. The center is somewhat deformed, however, it allows assessing its proportions as longer than broad, and as wide as high. In articular view, the neural arch is wider than the centrum, while the transverse processes are depressed dorsoventrally and recurved caudally. The combined breadth of both zygapophyses is similar to the total breadth of the centrum. The neural arch is similar in height to the centrum, showing a wide, sub-oval neural canal in articular view. Pliosauroidea Welles, 1943 (sensu Brown, 1981) Rhomaleosauridae Kuhn, 1961 Rhomaleosauridae indet. (Fig. 3E-M) Material―MUHNCAL.20173, postcranial fragmentary remains of a small individual. Location and Horizon―Ojo Opache, West of Calama, Región de Antofagasta. Caracoles Group (Tomlinson, 2001), Aalenian-Bajocian. Remarks―In their first description, Otero et al. (2020c) referred this specimen to Plesiosauria indet., however, these au-
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 57 thors indicated then affinities to the clade Rhomaleosauridae. Among the elements described, a putative phalanx actually shows general proportions with respect to the other bone elements that suggest its belonging to a zeugopodial and not acropodial element. Indeed, the morphology of that element is remarkably coincident with the radius of some rhomaleosaurids such as Meyerasaurus victori or Lindwurmia thuida (Smith and Vincent, 2010; Vincent and Storrs, 2019). The new anatomical identification of the radius adds to the characteristics of the pelvic girdle previously described in Otero et al. (2020c), whose general outlines look similar to some Rhomaleosauridae. With the new information, MUHNCAL.20173 is here referred to Rhomaleosauridae indet., being the second austral record of the clade (previously recorded in Argentina; Gasparini, 1997), and constituting a novel ecomorphotype, of small adult size. Figure 3: Plesiosauroidea indet. Isolated remains from the Bajocian of the Río Juntas sector, Copiapó. A) dorsal vertebra in anterior view; B) ventral view; C) left lateral view; D) Rib fragment. Modified from Burmeister and Giebel (1861). Rhomaleosauridae indet. E-F) Associated remains of a single small individual, exposed in different blocks, and recovered from Aalenian-Bajocian beds of Ojo Opache. G) Scheme of the preserved elements. Scale bar = 5 cm in all cases.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 58 Pliosauridae Seeley, 1874 aff. Pliosauridae indet. (Fig. 4A) Material—A dorsal vertebral centrum and part of a coracoid. Remains on display at the Museo Ruinas de Huanchaca, Antofagasta, documented during 2022. Location and Horizon―Sierra del Medio, north of Calama. Quehuita Formation, Lower Callovian. Remarks―These elements correspond to the material mentioned by Chong and Gasparini (1976) and Gasparini and Chong (1977), from Sierra del Medio, which was recovered in association with the holotype of ‘Metriorhynchus’ casamiquelai Gasparini and Chong (1977). The coracoid is a large table-like element, adhered to the rock matrix, which only preserves its lateral and posterior margin, showing a pronounced lateral cornua, while its anterior and symphyseal margins are absent. The vertebral centrum is also a large-sized element, consistent with the measurements of the coracoid (eventually suggesting a same individual), whose proportions are similarly broad as high, and almost twice high than its axially long. It has an amphicoelous body and dorsally, a marked depression consistent with the ventral margin of the neural canal. Although part of its ventrolateral surface is damaged, it is still possible to estimate the complete articular contour based on the preserved half, being almost circular in articular view. In ventral view, the centrum has two small subcentral foramina. On its dorsal surface, the breadth between the neural facets is slightly narrower than the centrum itself, while each neural pedicel has a broad contact surface with the centrum. The artricular characteristics of the center and the coracoid are consistent with a large Pliosauridae. The general shape of the centrum can be compared to posterior dorsal or even sacral centra of some pliosaurids (Linder, 1912; Barrientos et al., 2015; Fischer et al., 2015). However, the lack of more informative morphologies prevents referring it with greater confidence to its the clade Pliosauridae.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 59 Pliosauridae indet. (Fig. 4B) Material―MUHNCAL.20181, left mandibular ramus fragment. Locality and Horizon―Larga Sur, Cerritos Bayos, west of Calama. Cerro Campamento Formation, Middle Oxfordian. Remarks―The preserved elements include at least the location (sockets) of 5 teeth, whose orientation allows assessing that the fragment in question corresponds to the left mandibular ramus. At least one tooth is in an anatomical position, although naturally sectioned, preserving only a fragment of visible enamel, which corresponds to the apex of the lingual surface, showing fine striations. The spaces between the alveoli correspond to a very spongy tissue, with a large number of cavities, consistent with similar conditions previously described in Pliosauridae (Sassoon et al., 2015). On the internal (lingual) surface, a marked notch of the dentary is observed, consistent with the contact of another bone element, possibly the splenial. The general characteristics of the dentary, its dentition, and the characteristics of the tissue that makes up the partitions between alveoli, allow the material to be referred to a still undetermined Pliosauridae. Pliosauridae indet. (Fig. 4C-E) Material―MUHNCAL.20188, articulated individual, in the process of extraction. To date, a posterior fin (unprepared), an isolated femur, a humerus and part of a girdle, possibly pelvic (unprepared) have been recovered. Locality and Horizon―MUHNCAL.20188, informal locality Biese 3, Cerritos Bayos, west of Calama. Cerro Campamento Formation, lower Oxfordian. Remarks―To date, the materials listed here correspond to bone remains recovered from a more complete context, which includes at least part of a girdle, and likely the complete skull. These elements are in the process of being excavated in an area of hard logistical difficulty. Among the materials already recovered are a femur, collected in several naturally
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 60 rolled sections, plus an almost complete humerus, and part of a posterior fin not yet prepared. The anterior dentition of the skull and the characteristics of the propodials allow for the moment referring the specimen to an indeterminate Pliosauridae, pending the extraction of the rest of the skeleton, as well as its preparation and subsequent study. Figure 4: aff. Pliosauridae. A) Apparently associated remains of a large specimen. Fragment of coracoid and dorsal vertebral center on display at the Museo Ruinas de Huanchaca (photograph from April 2022), from the Calovian of Sierra del Medio, Antofagasta Region. Pliosauridae indet. B) MUHNCAL.20181, fragmentary mandibular ramus, from the middle Oxfordian of Loma Larga Sur, Cerritos Bayos sector. Pliosauridae indet. Associated remains from Biese 3 informal locality, lower Oxfordian, Cerro Campamento Formation. D) MUHNCAL.20188, in situ anterior tip of the skull, showing its dentition. E) Humerus of the same specimen. F) Femur of the same specimen. Scale bars = 10 cm, except in C = 5 cm.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 61 Plesiosauroidea Welles, 1943 Plesiosauroidea indet. (Fig. 5A-F) Material―T-334, a cervical vertebra (unlocatable), T-333, a dorsal vertebral center (missing), T-335 (original numbering in Tavera, 1981), a caudal center, currently deposited in the National Museum of Natural History (MNHN) under the acronym and number SGO.PV.15100. Location and Horizon―Quebrada de la Iglesia, 95 km southeast of Copiapó, Región de Atacama. Lautaro Formation, Middle Bajocian. Remarks―These vertebrae correspond to material initially identified as ichthyosaur remains by Tavera (1981). The elements illustrated by the latter author belong to a cervical vertebra (T334, missing), a dorsal centrum (T-333, missing) and a caudal centrum (T-335; currently SGO.PV.15100). The cervical vertebra (T-334) shows an almost circular articular contour, while its neural arch reaches almost two-thirds of the total breadth of the centrum. The centrum is broader than long (in axial direction), and has two subcentral foramina typical of the clade Plesiosauria (O’Keefe, 2001). It also preserves the proximal part of the left rib fused, allowing assessing that this is a simple articulation (‘single-headed’ sensu O’Keefe, 2001). The dorsal centrum (T-333) has a similar, almost circular articular contour, while dorsally, the facets of the neural arch reach a breadth similar to the centrum. In lateral view, the facets of the neural arch are slightly recessed on the lateral flank of the centrum. Finally, the caudal centrum (T-335=SGO.PV.15100) is somewhat deformed laterally, being probably depressed dorsoventrally. The centrum is broader than high and similarly high than long. In dorsal view it can be seen that the facets of the neural arch are displaced with respect to the middle part of the centrum, suggesting that its anterior articular facet corresponds to that with the neural arch shifted. In right lateral view it can be seen that the caudal facet is dorsoventrally higher than axially long. The relative sizes of the three elements, as well as their anatomical characteristics, are consistent with a single individual. The presence of fusion between the centers and the cervical and dorsal ribs suggests that the specimen was an adult (Brown, 1981). Similarly, the presence of a simple articulation in the cervical ribs (single-headed) indicates its belonging to
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 62 the Plesiosauroidea, for the moment, indeterminate. Figura 5: Plesiosauroidea indet. Associated remains from the Bajocian of Río Juntas sector, Copiapó (material currently lost). A) Cervical vertebra in articular view; B) Ventral view; C) Dorsal centrum in articular view; D) Lateral view; E) Caudal centrum in dorsal view; F) Lateral view. Scale bar = 20 mm.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 63 Cryptoclidia Ketchum and Benson, 2010 Cryptoclididae Williston, 1925 Cryptoclididae indet. (Fig. 6A, B) Material―MUHNCAL.20175, three dorsal vertebrae contained in a block. MUHNCAL.20172, an isolated dorsal centrum. Location and Horizon―MUHNCAL.20146 and MUHNCAL.20172, Cerro Campamento, West Calama. Cerro Campamento Formation, middle to upper Oxfordian. Remarks―MUHNCAL.20175 and MUHNCAL.20172 correspond to dorsal vertebrae with centra having articular surfaces with a heart-shaped contour, determined by a slightly keeled ventral margin, and a dorsal margin where the articulation of the transverse processes is broad and extends until the edge of the centrum. The presence of recurved and distally widened transverse processes is also informative in MUHNCAL.20175. These characteristics are coincident with those illustrated for dorsal vertebrae of some Cryptoclididae (Brown, 1981: fig. 9.4). Considering the latter, and given the absence of additional informative elements, both specimens are referred to as indeterminate Cryptoclididae. Genus Muraenosaurus Seeley, 1874 aff. Muraenosaurus sp. (Fig. 6C) Type Species—Muraenosaurus leedsi, NHMUK PV R.2421 (holotype). Peterborough, England, Callovian. Material―MUHNCAL.20146, a dental fragment preserving some teeth. Location and Locality and Horizon―MUHNCAL.20146, Quebrada Campamento, West Calama. Cerro Campamento Formation, middle to upper Oxfordian. Remarks―The teeth of MUHNCAL.20146 preserve part of the tooth enamel. The latter is smooth in its labial face, without visible striations. A tooth whose apex is absent still preserves their mold in the sandstone matrix, allowing observing
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 64 fine striations over the lingual surface. Among the known Cryptoclididae that preserve dental elements, the presence of lingual striations and absence of labial striations is only described for the genus Muraenosaurus (Brown, 1981: fig. 19). Although MUHNCAL.20146 corresponds to teeth of a size noticeably smaller than those illustrated by Brown (1981), its characteristics allow it to be distinguished from the genera Cryptoclidus and Kimmerosaurus, which lack striations on their lingual and labial surfaces, while the genus Tricleidus has teeth with profuse striations on both sides of the tooth (Brown, 1981: figs. 5, 24 and 39). Considering this evidence, MUHNCAL.20146 is here referred to as aff. Muraenosaurus sp. This determination would be expectable, given the presence of other local specimens previously referred to the same genus (Otero et al., 2020a). Muraenosaurus sp. (Fig.6 D-F) Material―MUHNCAL.20174, partial vertebral column preserving the posterior section of the neck and anterior section of the trunk; MUHNCAL.20176, fragmentary skeleton preserving teeth, cranial fragments, cervical, pectoral and dorsal vertebrae, part of its pectoral girdle, gastralia, a humerus and a partial femur. Location and Horizon―MUHNCAL.20174, Cerro Amarillo, Cerritos Bayos, West Calama, Región de Antofagasta; MUHNCAL.20176, informal locality Biese 3, Cerritos Bayos, West Calama, Región de Antofagasta. Both specimens come from the Cerro Campamento Formation, lower Oxfordian. Remarks―The absence of visible neurocentral sutures in MUHNCAL.20174 and MUHNCAL.20176 suggests that both individuals belong to adults (Brown, 1981). Along with this, both specimens have a matching vertebral size, in addition both show gracile neural pedicels and absence of notches on the ventral part of their centra. In both specimens, the posterior cervical vertebral centra acquire an oval-shaped articular contour. All of these characteristics are aspects previously described in the genus Muraenosaurus, and can be distinguished from other Cryptoclididae such as the genus Cryptoclidus, which possesses neural arches with thick pedicels in its cervical elements (Brown, 1981; fig. 8). On the other hand,
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 65 MUHNCAL.20176 preserves part of its coracoid which shows an axially extended contact in its midline, being consistent with a continuous symphysis without the presence of a cordiform fenestra. In addition, its respective humerus is noticeably thicker and longer than the femur, which is evident even when both elements are incomplete. All of these characteristics are present in the genus Muraenosaurus (Brown, 1981). Genus Vinialesaurus Gasparini, Bardet, and Iturralde-Vinent, 2001 Vinialesaurus sp. (Fig. 6F, G) Type Species―‘Cryptocleidus? cuervoi caroli’ De La Torre and Rojas, 1949 (Gasparini et al. (2001). Oxfordian of Cuba. Material―MUHNCAL.20205, a partial jaw. Locality and Horizon―Informal locality Biese 3, Cerritos Bayos, West of Calama, Región de Antofagasta. Cerro Campamento Formation, lower Oxfordian. Remarks―MUHNCAL.20205 was recovered in isolation and contained within a concretion. After its preparation, it was possible to compare the material with other plesiosaurs of the same age. In particular, both the general shape, its size and the number of alveoli present in MUHNCAL.20205 show a close similarity with the type material of Vinialesaurus caroli (Gasparini et al., 2001), which is also the only previously known specimen of the taxon. Considering this, MUHNCAL.20205 was referred to Vinialesaurus sp., but under open nomenclature, given the fragmentary nature of the material (Otero et al., 2020b). This specimen represents the second record of Vinialesaurus known so far.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 66 Figura 6: Cryptoclididae indet. A) Three dorsal vertebrae embedded in a block. Anterior view of the block. Middle-upper Oxfordian, Quebrada Campamento. B) MUHNCAL.20172, isolated dorsal centrum. aff. Muraenosaurus sp. C) MUHNCAL.20146, dentary fragment preserving few teeth. Middle-upper Oxfordian, Cerro Campamento. Muraenosaurus sp. D) MUHNCAL.20174, partial vertebral column form the neck-trunk portion. Cerro Amarillo, lower Oxfordian. E) MUHNCAL.20176, fragmentary skull. Biese 3 informal locality, lower Oxfordian. Vinialesaurus sp. F) MUHNCAL.20205, partial jaw in ventral view. Biese 3 informal locality, lower Oxfordian. G) same in oclussal view. All specimens from the Cerro Campamento Formation. Scale Bar = 5 cm in A, B, E; 10 mm in C; 10 cm in D; 50 cm in E.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 67 6. DISCUSSION 6.1. Plesiosaurs in northern Chile before the Middle Jurassic? Among the records of plesiosaurs known in Chile, there are only two mentions in rocks older than the Middle Jurassic. The presence of presumed plesiosaur gastralia from the Triassic of Los Molles was pointed out by Casamiquela (1973), while remains attributed to a plesiosaur fin, coming from Sinemurian levels of the Profeta Formation (locality of Cerro Campamento, south of Mina Escondida) were mentioned by Chong and Gasparini (1976). In neither case were descriptions or images of the material provided. In the case of Triassic gastralia, there is no way to reevaluate the material, reason why it is suggested to be rejected as a valid record. On the other hand, for the Sinemurian plesiosaur fin mentioned by Chong and Gasparini (1976), itts repository was indicated as the Humberto Fuenzalida Museum (Universidad Católica del Norte). However, efforts to find the material have been unsuccessful. Considering this situation, it is not possible to confirm for now the early presence of plesiosaurs in the Chilean Triassic, while their eventual presence in the Lower Jurassic remains pending confirmation, awaiting the appearance of this relevant material. Apart from the latter, there are currently no new records of plesiosaurs in the Lower Jurassic of Chile. 6.2. Plesiosaurs in northern Chile during the Middle Jurassic ‘Plesiosaurus neogaeus’ (Burmeister and Giebel, 1861) —The species ‘Plesiosaurus neogaeus’ (nomen dubium) proposed by Von Huene (1927) and based on a vertebra of Middle Bajocian age, constitutes the first historical determination of a Jurassic plesiosaur in Chile, and possibly also the first documented occurrence of plesiosaurs in the Jurassic of the southern hemisphere. Von Huene (1927) correctly recognized the affinities of the material illustrated by Burmeister and Giebel (1861), until then considered to be a marine crocodile (‘Teleosaurus neogaeus’; nomen dubium). The description provided by Burmeister and Giebel (1861) indicated that this vertebra measured 1 1/2” long, 1 1/3” high in the midline under
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 68 the neural canal, and 1 1/2” wide at the center. the same place. That is, the vertebral centrum is similarly long than broad, and slightly longer than high. Translated to centimeters, it corresponds to 3.8 cm long, 3.8 cm broad, and 3.4 cm high The aforementioned authors also pointed out the presence of two ‘vascular orifices’ (‘Gefässlöcher’) that unequivocally correspond to the typical subcentral foramina of Plesiosauria (O’Keefe, 2001). Burmeister and Giebel (1861) also indicated that the articular surfaces of the centrum were amphicoelous (concave), while the body of the vertebral centrum was medially waisted, shaped like an ‘hourglass’ (‘stundenuhrformige’). From the illustration provided by Burmeister and Giebel (1861: Tafel I) it is possible to recognize that the transverse processes are joined to the center by thick pedicels, delimiting a broader neural canal towards its base, and having a breadth similar to that of each pedicel. Furthermore, the neural arch is as wide as the center itself. Finally, in the available illustration a neurocentral suture is not observed, which leads to the assumption that it is an adult individual. The presence of two subcentral foramina on the ventral surface of the centrum is an unequivocal characteristic of Plesiosauria (O’Keefe, 2001; Benson and Druckenmiller, 2014), however, the general characteristics of this vertebra are quite unique within the group. The belted centrum, with amphicoelous articular faces, together with a neural arch as tall and wide as the centrum, are characteristics that resemble those observed among basal eosauropterygians (i.e., Pistosaurus, Pachypleurosaurus; see Carroll, 1988). In turn, in Plesiosauria, the size of the neural arch becomes comparatively smaller with respect to that of the centrum already in Early Jurassic taxa (e.g., Plesiosaurus dolichodeirus, Occitanosaurus tournemirensis; see Storrs, 1997; Bardet et al., 1999). In addition, the global record of Plesiosauria is especially scarce during the Aalenian-Bajocian (Sachs et al., 2019), adding difficulties to establish more meaningful comparisons. The small Plesiosauroidea of Tavera (1981) —While describing ichthyosaur remains from the Bajocian of the Lautaro Formation, Tavera (1981) inadvertently included a partial skull of a Metriorhynchoidea crocodile (recognized by Gasparini et al., 2000), as well as some postcranial elements of plesiosaurs (Otero et al., 2020c). At least three of the figured vertebrae can be identified as belonging to ple-
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 69 siosaurs, on the basis of their subcentral foramina (Tavera, 1981: Lam II, fig. 2) and by the presence of simple facets for the articulation of the ribs (Tavera, 1981: Lam II, fig. 2) 1981: Lam. III, figs. 1, 5, 7), contrary to the double facet joints present in ichthyosaur ribs (Maisch and Matzke, 2000 and references therein). In a previous review of Tavera’s (1981) original photographs, Otero et al. (2020c) for the first time referred these materials to Plesiosauria indet., identifying one centrum (T333) as dorsal, and two centra (T-334 and T-335) as sacral. In this sense, the present synthesis has once again reviewed the available information, noting that the elements belong to a cervical vertebra (T-334), a dorsal centrum (T-333), and a sacral centrum (T-335). The cervical vertebra was identified due to its rib facet located in the ventral half of the centrum, in addition to showing a subcircular articular face, and a neural arch narrower than the centrum, with apparently thin pedicels. The dorsal centrum shows a somewhat extended area on the dorsolateral margin, being coincident with the articulation of the transverse processes. This centrum has a rounded ventral contour and a slight angular dorsal contour. Finally, the sacral vertebra is deformed laterally, showing a centrum that is broader than high and higher than long, with a rib facet located in an intermediate position between the neural arch and the centrum. In turn, the neural arch is slightly shifted anteriorly, suggesting a degree of overlapping with the immediately anterior element, although the neural spine and part of the arch are absent. The three vertebral elements are coincident in size, while none of them show neurocentral suture lines, suggesting that they belong to an adult (Brown, 1981). Given their common stratigraphic origin (Jensen, 1976), their coincident ontogenetic stage, anatomically coincident size, and similar preservation, they are here considered as the same individual. The presence of a cervical vertebra with simple facets for the cervical ribs allows the material to be distinguished with respect to basal forms from the Lower Jurassic (Stratesaurus, Avalonnectes, Eoplesiosaurus) and also from all Pliosauridae + Rhomaleosauridae (Benson et al., 2012; Benson and Druckenmiller, 2014). Based on this information, the material initially described by Tavera (1981) and belongjn to at least 3 vertebrae, is here referred to an indeterminate Plesiosauroidea. Another additional element representing the proximal part of a propodium (Tavera, 1981: Lam. III, fig. 2), also shows anatomical aspects typical of plesiosaurs (i.e., pro-
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 70 minent articular head, flattened diaphysis), and could eventually belong to the same individual. Rhomaleosauridae from Ojo Opache —The specimen MUHNCAL.20173, from Aalenian-Bajocian levels of the Caracoles Group, was previously described by Otero et al. (2020c) and then referred to Plesiosauria indet. The reevaluation of the remains has allowed reassessing that an element previously identified as a phalanx, actually corresponds to a radius. Indeed, the relative proportions of the radius are better consistent with the size of the preserved vertebrae, as well as the remains of the pelvic girdle available. The shape of the radius is quite unique, its outline being comparable with the same element in the Rhomaleosauridae Meyerasaurus victori (Smith and Vincent, 2010: fig. 4D) and Lindwurmia thuida (Vincent and Storrs, 2019: fig. 5J). Previously, Otero et al. (2020c) pointed out for MUHNCAL.20173, possible affinities with Rhomaleosauridae, based on the outline of the preserved pelvic girdle elements. With the addition of the radius, it has been possible to strengthen this previous opinion, reason why the specimen is here referred to as a small indeterminate Rhomaleosauridae. In the South American continent, there is only one previous record of a Bajocian Rhomaleosauridae in Argentina, represented by Maresaurus coccai Gasparini, 1997, a large taxon that evidently differs from the Chilean form. In any case, among the Rhomaleosauridae there are some small basal taxa, such as Lindwurmia thuida (Vincent and Storrs, 2019). aff. Pliosauridae of Sierra del Medio —Since its opening, and at least until 2022, the Museo Ruinas de Huanchaca (Antofagasta) inlcuded in its exhibition plesiosaur remains from Sierra del Medio, a locality north of Calama. These remains were previously reported (although never described) in the publication of the holotype of ‘Metriorhynchus’ casamiquelai Gasparini and Chong (1977). The age of the material was specified by Gasparini et al. (2008), belonging to lower Callovian levels of the Quehuita Formation. The remains comprise a large fragment of a coracoid and a large vertebra, presumably found in association. The coracoid fragment remains attached to the sedimentary matrix, with both its anterior and symphyseal margins being absent. The lateral margin shows a prominent cornua and a medial cons-
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 71 triction. The vertebral centrum has one damaged side, while its opposite side is well preserved, allowing evaluation of the complete articular contour, which has a rounded ventral margin, while its dorsal margin represents the maximum breadth of the centrum, with two articular facets for the transverse processes, allowing the center to be identified as a dorsal element. This center is as broad as it is high, and almost twice as broad as it is long. It has amphicoelous (concave) articular surfaces and a marked dorsal depression consistent with the ventral surface of the neural canal. Two small subcentral foramina can be seen on the ventral surface of the centrum. The large size of both elements suggests their belonging to Pliosauridae, however, no definitive characteristics are preserved that would ensure their taxonomic determination at a more significant level. For this reason, it is referred to here as aff. Pliosauridae. Other records in the Callovian of northern Chile —There are mentions of remains referred to plesiosaurs in the Cerritos Bayos area, and particularly, in strata of Callovian age (Biese, 1957; 1961). Unfortunately, the repository of these materials is unknown, and they were never described or figured, making their present reevaluation impossible. 6.3. Plesiosaurs in northern Chile during the Upper Jurassic Pliosauridae and Cryptoclididae of Cerritos Bayos —So far, the record of plesiosaurs from the Upper Jurassic of northern Chile is restricted only to the Oxfordian (Biese, 1957; 1961; Chong and Gasparini, 1976; Gasparini, 1979; 1985). During recent years it has been possible to recover new specimens that have been informative even at the genus level. The presence of still undetermined Pliosauridae has been documented in two localities in Cerritos Bayos, belonging to the lower Oxfordian and middle Oxfordian (Otero et al., 2020a). These adds to the Sierra del Medio remains from Callovian levels (Gasparini and Chong, 1977), suggesting that Pliosauridae were present in the marine basins of northern Chile from the Middle Jurassic and onwards. At the moment, no remains of Pliosauridae younger than the Oxfordian are known in Chile, however, the group has been reported in Tithonian levels
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 72 of the Neuquén Basin, Argentina (Gasparini, 2007; Gasparini and O’Gorman, 2014). In turn, the South American records of cryptoclidid plesiosaurs have been limited to material of Callovian age recovered in the Neuquén Basin, indicating the presence of cf. Muraenosaurus sp. and cf. Cryptoclidus sp. (Gasparini and Spaletti, 1993; Gasparini, 2007). The known record in northern Chile allows us to complement the presence of the group during the Oxfordian, adding records referable to Muraenosaurus sp. and to Vinialesaurus sp. (Otero et al., 2020b). At the moment more recent records of austral Cryptoclididae are unknown. 6.4. Paleoecology The record of plesiosaurs in northern Chile is still meager, however, the available material allows a first approach to the diversity that inhabited these latitudes, especially during the Jurassic, which regionally, is the best documented period. However, at the moment it is not possible to ensure the presence of Triassic plesiosaurs in Chile, although the record of Casamiquela (1973) opens interesting perspectives for the search for new remains that may be informative. The Chilean forms of the Lower Jurassic are still indeterminate. At the moment they are valuable for locally documenting the group during this period, but they lack more relevant information in this regard. During the Middle Jurassic, there is a scarce global record of plesiosaurs prior to the Callovian and especially during the Bajocian (Buchy, 2004; Gasparini, 1997; Godefroit, 1994; Kear, 2012; Vincent et al., 2007; Sachs et al., 2019 ). The presence of small indeterminate plesiosauroids in the Bajocian of Cerro Blanco, Copiapó Region, is documented by two different finds (Burmeister and Giebel, 1861; Tavera, 1981). In turn, the presence of a non-plesiosauroid represented by the specimen referable to Rhomaleosauridae indet. from the Aalenian-Bajocian of Ojo Opache (Región de Antofagasta), coincidentally it also corresponds to a small adult. These small adults suggest an ecological role as secondary or tertiary consumers, considering their reduced estimated length (roughly about 2 to 2.5 m). During the Middle Jurassic and especially since the Calovian, the presence of Metriorhynchoidea crocodiles in some cases directly associated with these records, reaffirms a possible role of the local Plesiosauria as minor macropredators. From the Callovian and onwards, the local Plesiosauria begin to encompass new aspects, now including high-level
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 73 consumers and possibly apex predators, judging by the remains of aff. Pliosauridae from Sierra del Medio, and by the Pliosauridae material from Cerritos Bayos. The estimated size for the latter exceeds 7 m and it has robust teeth, being a predator unequivocally larger than the Metriorhynchidae locally documented in the same basin (Soto Acuña et al., 2015a, b; 2018) and also larger than the known macropredatory actinopterygians in the same geological unit (Otero, 2022). In turn, the most complete remains of Cryptoclididae allow us to estimate an approximate length of about 5 to 6 m (based on MUHNCAL. 20176). In particular, the dentition known in the genera Muraenosaurus and Vinialesaurus suggests an eminently piscivorous diet and/or soft-bodied benthic animals. 6.5. Paleobiogeography During the Early Jurassic there is scarce information on the marine vertebrates of northern Chile. Partial evidence suggests that the apex predators could have belonged to large ichthyosaurs, judging by the remains found in Hettangian rocks in Pan de Azúcar, Región de Atacama, and in Hettangian-Sinemurian rocks in Mantos Blancos, Región de Antofagasta (Suárez and Otero, 2010; Pardo-Pérez et al., 2015; Otero and Sepúlveda, 2020). Other remains of indeterminate ichthyosaurs have been recorded in the Early Jurassic of northern Chile (Casamiquela, 1970; Chong and Gasparini, 1972; 1976; Pardo-Pérez et al., 2015), proving the abundance of the group during this period. On the contrary, records of plesiosaurs are scarcer, corresponding to fragmentary material found in Sinemurian rocks from the Región de Antofagasta (Chong and Gasparini, 1976), being barely informative. In turn, the presence of thalattosuchian crocodiles (Chong and Gasparini, 1972), plus actinopterygians Leptolepidae and Mawsoniidae in the Sinemurian of Chile (Arratia, 2015; Arratia and Schultze, 2015), add evidence about a bi-hemispheric distribution of the groups during the Early Jurassic, with an exchange of fauna between the Tethys and Panthalassa through marine corridors linked to the fragmentation between Gondwana and Laurasia. Candidates for these marine routes are the Boreal Corridor, the Austral Corridor, and the Mozambique Corridor (Benedetto, 2010). From the Middle Jurassic and especially during the Late Jurassic, there is more solid evidence about bi-hemispheric exchange in the marine vertebrate fauna. The presence of Rhomaleosauridae in the
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 74 Bajocian of Argentina and Chile suggests an early exchange already during the Middle Jurassic. From the Late Jurassic onwards, this exchange hypothesis is better supported by the common record of Metriorhynchidae crocodiles, Ophthalmosauridae ichthyosaurs, Pliosauridae and Cryptoclididae plesiosaurs both on the southwestern coasts of Gondwana and in the Tethys Sea. The Cryptoclididae also include the only record of Vinialesaurus outside the Caribbean, reinforcing the hypothesis of an exchange through the Caribbean Marine Seaway (Iturralde-Vinent, 2003). Additionally, the actinopterygians from the Middle-Upper Jurassic of northern Chile include highly endemic elements (Arratia, 1981; 1982; 1986; Arratia et al., 1975a; 1975b; 1975c), but also with elements shared with the Tethys, represented by material referable to Scheenstia sp., Leedsichthys, aff. Hypsocormus sp., and other still undetermined Pachycormidae (Otero, 2022). 7. CONCLUSIONS The fossil record of plesiosaurs in northern Chile has been recognized since the second half of the 19th century. Locally, the group has finds restricted to the Jurassic, except for a dubious mention of fragmentary remains from the Triassic, which cannot currently be confirmed. The Early Jurassic forms have not been informative so far, however, they have allowed documenting the presence of the group in Sinemurian levels of the Región de Antofagasta. From the Middle Jurassic onwards there are more informative remains. Two finds in the Región de Atacama show the presence of indeterminate plesiosauroids, represented by small adult forms, estimated at 2 to 2.5 m. In turn, in the Región de Antofagasta the presence of a third taxon corresponding to a small adult has been documented, which has been referred to an indeterminate Rhomaleosauridae. Since the Late Jurassic, Plesiosauria achieved new ecological roles, probably positioning themselves as apex predators in the systems of northern Chile. In this regard, a Callovian specimen of a possible large Pliosauridae is documented, and two additional specimens of Pliosauride of Oxfordian age, one of which allows us to infer a body length of about 7 meters. Among the Oxfordian forms of Chile, there are also multiple records of Cryptoclididae, until now represented by the genera Muraenosaurus and Vinialesaurus.
MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE 75 This diversity of plesiosaurs known so far allows complementing the knowledge about the marine vertebrates that inhabited northern Chile during the Jurassic, adding to the valuable records of actinopterygians, metriorhynchid crocodiles, and ophthalmosaurid ichthyosaurs previously known regionally. The evidence available so far suggests that the fauna of marine reptiles and Jurassic actinopterygians of northern Chile was the result of an exchange with similar elements from the northern hemisphere, through marine corridors. This exchange should started at least during the Early Jurassic, coupled to the separation of Gondwana and Laurasia, but the routes are still difficult to elucidate. Since the Middle Jurassic and especially during the Late Jurassic, the evidence points to an exchange of fauna primarily through the Caribbean Seaway, which does not rule out other possible secondary routes. Finally, the persistent presence of plesiosaurs during much of the Jurassic exposed in Chilean territory opens important perspectives for the future study of the group. REFERENCES Arratia, G. 1981. Varasichthys ariasi n. gen. et sp. from the Upper Jurassic from Chile (Pisces, Teleostei, Varasichthyidae n. fam.). Palaeontographica A 175:107–139. Arratia, G. 1982. Chongichthys dentatus, new genus and species, from the Late Jurassic of Chile (Pisces: Teleostei: Chongichthyidae, new family), Journal of Vertebrate Paleontology 2:133–149. Arratia, G. 1986. New Jurassic fishes (Teleostei) of Cordillera de Domeyko, northern Chile. Palaeontographica A 192:75–91. Arratia, G. 2015. Los peces osteíctios fósiles de Chile y su importancia en los contextos paleobiogeográfico y evolutivo. En: Rubilar-Rogers, D.; Otero, R.A.; Vargas, A.; Sallaberry, M. (eds.), Vertebrados Fósiles de Chile. Publicación Ocasional del Museo Nacional de Historia Natural, Chile, 63:35–83. Arratia, G.; Schultze, H. P. 2015. A new fossil actinistian from the Early Jurassic of Chile and its bearing on the phylogeny of Actinistia. Journal of Vertebrate Paleontology e983524: 12 p. Arratia, G.; Chang, A.; Chong, G. 1975a. Leptolepis opercularis n. sp. of the Upper Jurassic from Chile. Ameghiniana 12:350–358. Arratia, G.; Chang, A.; Chong, G. 1975b. Sobre un pez fósil del Jurásico de Chile y sus relaciones con clupeidos sudamericanos vivientes. Revista Geológica de Chile 2:20–31. Arratia, G.; Chang, A.; Chong, G. 1975c. Pholidophorus domeykanus n. sp. del Jurásico de Chile. Revista Geológica de Chile 2:1–19.
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MUSEO DE HISTORIA NATURAL Y CULTURAL DEL DESIERTO DE ATACAMA CALAMA, CHILE Avenida Bernardo O Higgins s/n. Interior Parque El Loa, Calama, Chile.