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.

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.

[4] 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.

[4] 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.

[5] Patagosaurus is almost completely known with many articulated specimens found covering almost all of the skeleton, including parts of the skull.

[2][4] MACN CH 933 is directly comparable with the type material of Patagosaurus, which confirms its association with the genus.

[4] 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.

MPEF-PV 1670 shows what the morphology of the adult or subadult skull was like, while MACN CH 933 represents a juvenile individual.

The cervical, caudal and dorsal vertebrae are generally similar to Camarasaurus, although the sacrum possesses 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.

[2] The hindlimbs of Patagosaurus are based on scant material, some femora, a tibia and a few nondescript pedal bones.

The forelimb of Patagosaurus is much more gracile and different from the robust later sauropods like Camarasaurus and Apatosaurus, and instead resembles more Diplodocus.

Features uniting the genera were identified in the pelvic structure and vertebrae, specifically the caudal neural spines and the ilium and ischium.

[11] 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.

[14] The Cañadón Asfalto Formation, which was deposited about 179-178 million years ago,[5] was a lush ecosystem, in which many organisms lived.

[14] The fauna is dominated by tetrapods, ranging from aquatic amphibians to terrestrial turtles, mammals and dinosaurs.