Patagosaurus

*Patagosaurus fariasi*

***Patagosaurus*** (meaning "Patagonian lizard") was a large herbivorous dinosaur from the long-necked group Sauropoda. It reached a length of 18 meters. Similar to other primitive eusauropods, it was rather heavily built and similar to *Cetiosaurus* in general appearance. It is known from a dozen individuals, though some referred material may belong to another related dinosaur genus. It lived during the Callovian of the Middle Jurassic (163-161 mya) in what is now Argentina. Other Argentinian dinosaurs living approximately at the same time were *Piatnitzkysaurus*, *Condorraptor* and *Amygdalodon*.

It was described by Jose Bonaparte in 1979. The type species is P. fariasi. Some authors (such as Bonaparte and Upchurch) have placed *Patagosaurus* in the family Cetiosauridae, but not all paleontologists agree; sauropod classifications are still uncertain.

## 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 Jose 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 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, 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 post cranial 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 934, 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 t (7.76 long tons; 8.69 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 (10.41 short tons; 9.29 long tons) in weight, similar to the later estimates by Holtz.[1] A 2006 study by Donald M. Henderson calculated the weight of *Patagosaurus* to be 7.89 t (7.77 long tons; 8.70 short tons), a smaller estimate than McIntosh's.

The skull of *Patagosaurus* is not very well known, with a 2003 revision by Oliver Rahut determining only a few jaws are certainly referable 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.[8] The teeth also possess marginal denticles on the crown. Based on histological studies, an individual of *Patagosaurus* would have replaced all its teeth within 58 days, similar to 62 days for *Camarasaurus*, and 34 days for *Diplodocus*.

## Postcranial skeleton

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 540 mm (21 in), with the total sacral length being 920 mm (36 in).

The pelvic girdle is well-preserved and well studied. In the holotype, the pelvic girdle is almost complete, only lacking the proximal ends of each ischium. The ilia of the holotype are well known, and show many distinct features. The pubic peduncle, where the ilium articulates with the pubis, is long and straight and has an expansion on the end, as in many sauropods. The upper edge of the iliac blade is curved and thick, with rugosities (rough spots) for cartilage attachment. The pubic elements are large and robust in adults, more so than in juveniles. They are flat when viewed from in front, and convex when seen from behind. *Lapparentosaurus* resembles Patagosaurus when comparing their pubes. The ischia are much more gracile than the pubes, and only have a small distal expansion. While the ilia resemble *Barapasaurus*, and the pubes resemble *Lapparentosaurus*, the ischia are most similar to *Diplodocus* and *Apatosaurus*.

The hindlimbs of *Patagosaurus* are based on scant material, some femora, a tibia, and a few nondescript pedal bones. Two femora come from an adult, with a single additional bone known from the juvenile. The adult femora are proportionately different from the juvenile, being mostly straighter and more ovoid in cross-section. The femoral head is well preserved, although lacking the greater trochanter. The distal end is rather symmetrical when viewed from behind, with two similarly sized condylar surfaces. In the juvenile, the fourth trochanter is completely in the proximal end. The tibia has a well-developed cnemial crest, and is also short and robust. The surface that would have articulated with the astragalus in life has the anterior half raised, and the posterior half lowered.

The pectoral girdle is well known. Both the left and right scapulae and coracoids are known, though incomplete. The scapulae are large, and robust, and thicken as they near the glenoids. The scapular blades are flat, although they are both convex along the anterior edge. Where the scapulae and coracoids articulate, the coracoids are thickest, and they become gradually thinner as they gain distance from the scapulae. The younger specimen of Patagosaurus possesses a slightly different morphology of the pectoral girdle, with slightly differing proportions, such as a slightly smaller scapular blade. The coracoids resemble *Barapasaurus* in shape, and differ from *Camarasaurus*, although they cannot be directly compared with those of *Cetiosaurus*.

The forelimbs of *Patagosaurus* are only based on three bones from the juvenile specimen, and no manual elements are preserved. The humeri are slender and elongate, lacking great proximal and distal expansions. The incomplete deltoid crest, only shows that it was wide, and likely had a projection below and behind. Like the humeri, the radius is slender, and lacks large expansions on either end. On the edge closest to the ulna, the radius possesses a ridge along its edge, which corresponds to where radioulnar ligaments would have attached. The ulna is complete, although sediment-filled breaks might have altered its original shape. The forelimb of *Patagosaurus* is much more gracile and different from the robust later sauropods like *Camarasaurus*, and *Apatosaurus*, and instead resembles more *Diplodocus*.

## Classification

When originally described, *Patagosaurus* was identified as a relative of *Cetiosaurus* in the family Cetiosauridae. It can be distinguished from *Cetiosaurus*, a similar genus, by features of the ischium and vertebrae. Another genus also identified as a cetiosaurid by Bonaparte, *Volkheimeria*, was named in the same paper as *Patagosaurus*. Features uniting the genera were identified in the pelvic structure and vertebrae, specifically the caudal neural spines and the ilium and ischium. These characteristics show that the genera are more derived than *Amygdalodon*, yet more primitive than *Haplocanthosaurus*.

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:

## Paleoecology

*Patagosaurus* was uncovered in the Middle Jurassic Cañadon Asfalto Formation, which preserves a large variety of flora and fauna. In fact, Escapa et al. noted that "the fossil record of this formation represents the most completely known biota from the continental Middle to Late Jurassic of the Southern Hemisphere and one of the most complete of the entire world".[12] The Cañadon Asfalto Formation, which was deposited about 165 to 161 million years ago, was a lush ecosystem, in which many organisms lived. In the Middle Jurassic, the region would have been part of the great southern landmass of Gondwana. Most of the plants are conifers, although ferns and equisetales are also abundant. Directly below the formation is a layer of ash, indicating a nearby volcano.

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*.

## JPInstitute.com Description

Patagosaurus was a large member of the plant-eating, long-necked sauropods. It was related to Cetiosaurus and lived at about the same time. What makes it important is that it was found in South America and since Cetiosaurus was in Europe and Africa, it shows that these huge sauropods traveled from one continent to another.

Patagosaurus is the oldest known South American sauropod. It is known from a dozen individuals found in the same formation.

## Links

http://web.archive.org/web/20040214162320fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_patag.html