Patagosaurus

Extinct genus of dinosaurs

Patagosaurus (meaning "Patagonia lizard") is an extinct genus of eusauropod dinosaur from the Middle Late Toarcian of Patagonia, Argentina. It was first found in deposits of the Cañadón Asfalto Formation, which date to around 179 to 177 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 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 being quadrupedal. 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.

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. 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. 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, An earlier estimate by John S. McIntosh and his colleagues in 1997, found that Patagosaurus was approximately long, and also in weight, similar to the later estimates by Holtz. 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 also possess marginal denticles on the crown.

Most of the postcranial skeleton is known in Patagosaurus. The cervical, caudal and dorsal vertebrae are generally similar to Camarasaurus, although the sacrum possesses many distinct features. The sacrum is well preserved, showing that Patagosaurus possessed five sacral vertebrae. All the vertebrae but the fifth are fused together. All the neural spines are tall, and the centra are occasionally transversely narrow. The neural canal of the vertebrae is unique among sauropods, however. Starting from the very end of the first vertebra, and extending to almost the end of the third there is an enlargement of the canal, forming a well defined cavity. Even though the sacrum itself is distinguishing, its sacral ribs resemble Camarasaurus. The sacral vertebrae have a total length of , with the total sacral length being
Later in 1995, Paul Upchurch published a paper on early sauropods, finding Patagosaurus as a cetiosaurid again. He found that although earlier works had distinguished two groups, the shunosaurines and cetiosaurines, in the family, but that Shunosaurus and relatives were actually closer to Euhelopus, and cetiosaurines (Cetiosaurus, Patagosaurus and Amygdalodon) were the only true cetiosaurids. Upchurch noted, however, that further work on the group might reveal different conclusions. In a 2009 revision of Euhelopus, Jeffrey A. Wilson and Upchurch published a joint analysis on primitive eusauropodan relationships. They found that Patagosaurus was in fact not a sister taxon of Cetiosaurus, but instead more basal than the genus, effectively invalidating Cetiosauridae. Their results are shown below:

A 2021 study found Patagosaurus to be a member of the Cetiosauridae.

Patagosaurus was uncovered in the Jurassic Cañadón Asfalto Formation, originally thought to be Middle or Late Jurassic, but found recently to be Late Early Jurassic (Middle Toarcian) in age. The fauna is dominated by tetrapods, ranging from aquatic amphibians to terrestrial turtles, mammals and dinosaurs. The sole amphibian known is Notobatrachus; turtles are represented by a distinct form that was named Condorchelys; mammals are known from a few genera, including Argentoconodon, Asfaltomylos and Henosferus; multiple dinosaurs have been identified, including the sauropods Volkheimeria, Patagosaurus and a potential third genus that is yet unnamed, and theropods include the related Piatnitzkysaurus and Condorraptor.