Patagosaurus (meaning "Patagonia lizard") is an extinct genus of eusauropod dinosaur from the middle Toarcian of Patagonia, Argentina. It was first found in deposits of the Cañadón Asfalto Formation, which date to around 178 million years ago. Although originally twelve specimens were assigned to the taxon, at least one of them may belong to a different genus. Patagosaurus probably lived alongside genera such as Piatnitzkysaurus, Condorraptor, and Volkheimeria. Since Patagosaurus is known from many specimens, including at least one juvenile, its anatomy and growth are fairly well understood. Both ages exhibit the typical features of a sauropod: a long neck, small head, a long tail, and quadrupedal stance. The juvenile exhibits features different from the adult in regions like the mandible, pectoral girdle, pelvis, and hindlimb, although overall their anatomy is quite similar. The many known specimens help fill in gaps in the anatomy of the genus, such as the forelimb and skull. Parts of the skeleton, like the pectoral girdle, tibia, and pubis are more robust, while others, like the forelimb and ischium, are more gracile. The material of Patagosaurus is similar to closely related taxa like Cetiosaurus and Volkheimeria, more primitive genera such as Barapasaurus and Amygdalodon, and more derived sauropods like Diplodocus and Camarasaurus.
Discovery and naming
In the 1970s many specimens of a previously unidentified dinosaur were found associated together in the same bed and locality: a pebbly stratum near a route to Cerro Condor. The specimens were first described by José Bonaparte in 1979. For the fossil he erected the genus Patagosaurus, as well as its type species P. fariasi. The generic name of Patagosaurus comes from the location of its find in Patagonia, and the fact that it is a reptile. The specific name honours Ricardo Farias, on whose land the initial discovery was made. The genus was originally known from an almost complete postcranial skeleton lacking a skull as the holotype, and many referred specimens; however, in 2003 it was found that a dentary was referable to the species, so more specimens are probably this taxon. Its skeleton was found near those of Piatnitzkysaurus and Volkheimeria in the layers originally suggested as Callovian- to Oxfordian-aged Patagonian deposits of the Cañadón Asfalto Formation. These layers have been recently re-dated, finding out thanks to advanced zircon datation that the bones of the three genera and all the vertebrates of Las Charcitas member where deposited in between 179 and 178 million years, that is Middle-Late Toarcian. Patagosaurus is almost completely known with many articulated specimens found covering almost all of the skeleton, including parts of the skull. Over twelve specimens have been referred to the species, although some of the material is probably from a unique taxon. Bonaparte (1986) assigned three specimens other than the holotype PVL 4170, PVL 4076, MACN CH 934 and MACN CH 933 to the genus. While the holotype includes a postcranial skeleton, the others are known from cranial material and a nearly complete juvenile skeleton and skull. MACN CH 933 is directly comparable with the type material of Patagosaurus, which confirms its association with the genus. A specimen first referred to Patagosaurus in 2003, MPEF-PV 1670 (which includes just a lower jaw), is also very similar to MACN CH 933, and differences can be associated with age, so therefore, MPEF-PV 1670 presumably represents adult cranial material. However, the teeth of MACN CH 934 are very different from those of both lower jaws (MACN CH 933 and MPEF-PV 1670), so it can be identified as another sauropod from the same deposit as Patagosaurus. Thus, the taxon only certainly includes PVL 4170, MACN CH 933 and MPEF-PV 1670.
Description
Patagosaurus is a sauropod that possessed a general and unspecialized bauplan of being quadrupedal, having an elongate neck, a small head and a very long tail. Therefore, it is similar to Cetiosaurus and other related genera, who possessed the same morphology. It has been estimated that it was about 16.5 m (54 ft) long and weighed about 7.88 tonnes (7.8 long tons; 8.7 short tons). An earlier estimate by John S. McIntosh and his colleagues in 1997, found that Patagosaurus was approximately 15 m (49 ft) long, and also 9.44 metric tons (9.3 long tons; 10.4 short tons) in weight, similar to the later estimates by Holtz. A 2006 study by Donald M. Henderson calculated the weight of Patagosaurus to be 7.89 t (7.8 long tons; 8.7 short tons), a smaller estimate than McIntosh's. The skull of Patagosaurus is not very well known, with a 2003 revision by Oliver Rauhut determining only a few jaws are certainly referrable to it, as opposed to nearly the entire skull. MPEF-PV 1670 shows what the morphology of the adult or subadult skull was like, while MACN CH 933 represents a juvenile individual. Based upon how broad, high and short the adult articulated mandibles of Patagosaurus are, its snout would have been short, high and broad as well, a typical feature of most sauropods. The teeth of Patagosaurus are reminiscent of more derived sauropods. They are similar in morphology to Euhelopus, being concave on one side as well as having crowns with fairly great expansions. They are also similar to Camarasaurus, although the latter genus has less of a concavity and expansion. The teeth also possess marginal denticles on the crown. Based on histological studies, an individual of Patagosaurus would have replaced a tooth every 58 days, similar to 62 days for Camarasaurus, and 34 days for Diplodocus.
Postcranial skeleton
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