Pronunciation: RO-kah-SOR-us
Meaning: Roca City Lizard
Author/s: Salgado and Azpilicueta (2000)
Synonyms: None known
First Discovery: Salitral Moreno, Argentina
Discovery Chart Position: #470
Rocasaurus muniozi
Salgado and Azpilicueta named Rocasaurus in 2000 on the strength of a holotype thigh, some pelvic bones and vertebrae, which is a depressingly decent haul for an Argentine sauropod. And they were initially thought to belong to a juvenile, but further discoveries showed that not to be the case.
Its closest relative is the slightly younger Saltasaurus loricatus, anchor of the titanosaurian sub-family Saltasaurinae, whose Malteser-boned members are modestly sized for sauropods. At an estimated adult length of eight meters from snout to tail-tip and maybe four tons in weight, Rocasaurus was small, even for a saltasaurine. But being built to dine on lower-lying vegetation meant it avoided being eaten into extinction by its larger, long-necked, treetop-hogging contemporaries.
What was initially thought to be another dinky saltasaurine — Bonatitan reigi — was discovered in the same formation as Rocatitan and described by Martinelli and Forasiepi in 2004. Bone-wise, the only part present in both specimens that could be compared was a thigh, and they were remarkably similar, differing only in the design of the distal condyles (two bulbous bits on the end that join the knee): they are both roughly the same size in Rocasaurus, but one is bigger than the other in Bonatitan. However, during a restudy in 2014 by Salgado and colleagues, they realised not only that the two listed specimens of Bonatitan belonged to five individuals of different sizes with the original holotype accounting for three, but also that Bonatitan wasn't a saltasaurine at all.
What was initially thought to be another dinky saltasaurine — Bonatitan reigi — was discovered in the same formation as Rocatitan and described by Martinelli and Forasiepi in 2004. Bone-wise, the only part present in both specimens that could be compared was a thigh, and they were remarkably similar, differing only in the design of the distal condyles (two bulbous bits on the end that join the knee): they are both roughly the same size in Rocasaurus, but one is bigger than the other in Bonatitan. However, during a restudy in 2014 by Salgado and colleagues, they realised not only that the two listed specimens of Bonatitan belonged to five individuals of different sizes with the original holotype accounting for three, but also that Bonatitan wasn't a saltasaurine at all.
(Juan Carlos Muñoz' General Roca Lizard)Etymology
Rocasaurus is derived from "General Roca" (the city close to its place of discovery) and the Greek "sauros" (lizard). The species epithet, muniozi (moo-NYOH-sie), is named for Juan Carlos Muñoz, director of the Paleontology Area of the "Carlos Ameghino" Museum in Cipolleti, for his long-term support of palaeontological investigations in the region.
Discovery
The remains of Rocasaurus were discovered in the Allen Formation at Salitral Moreno, near the city of General Roca, Río Negro Province, Patagonia, Argentina.
The holotype (MPCA-Pv 46/1—16) consists of a left femur (thigh), pelvic bones (both ischia, left pubis, the left ilium and a fragment of the right one), one partial cervical (neck) vertebra, two partial dorsal (back) vertebrae, two tail vertebrae, and several neural arches.
