Prolacerta is a genus of archosauromorph reptile from the lower Triassic of South Africa and Antarctica. The only known species is Prolacerta broomi. Prolacerta was a small and slender animal with a rather long neck, low skull, and serrated teeth. It would have resembled a modern monitor lizard at a quick glance, though this is an example of convergent evolution as opposed to close affinities. When first discovered, Prolacerta was considered to be ancestral to modern lizards ("lacertilians"). However, a study by Gow (1975) instead found that it shared more similarities with the lineage that would lead to archosaurs such as crocodilians and dinosaurs (including birds). Prolacerta is now understood to be one of the most well-known early members of this lineage, formally known as Archosauromorpha. Some paleontologists have previously used the term "Prolacertiformes" in reference to superficially lizard-like early archosauromorphs, though the usage of Prolacertiformes as a valid group has lost support in recent decades. Many modern paleontologists consider Prolacerta to be among the closest relatives of the Archosauriformes, an advanced group of archosauromorphs including true archosaurs.
History of discovery
South African fossils Prolacerta was first described by Francis Rex Parrington in 1935 from a single skull discovered near the small town of Middelburg in the Eastern Cape of South Africa. The fossil was recovered from an exposure of rock from the Katberg Formation in the Lystrosaurus Assemblage Zone. This original skull, the holotype, is now stored at the Cambridge University Museum of Zoology as specimen UMZC 2003.40 (or UCMZ 2003.41R). The generic name Prolacerta is derived from Latin, meaning "before lizard", and its species name broomi is in commemoration of the famous paleontologist Robert Broom, who discovered and studied many of the fossils found in rocks of the Karoo Supergroup. Beyond Parrington's original skull fossil, additional skull material was slowly accumulated over the course of the mid-20th century. One skull, BPI 471, was originally described as a new genus and species, Pricea longiceps, by Broom and Robinson (1948). Later authors concluded that Pricea was a junior synonym of Prolacerta, only distinguishable by its style of preservation. As of 2018, 25 different Prolacerta specimens have been found in South Africa. One (the holotype) is accessioned at Cambridge, one at UCMP (University of California Museum of Paleontology), 7 at BPI (Bernard Price Institute for Palaeontological Research), 2 at NMQR (National Museum, Bloemfontein), 13 at SAM-PK (Iziko South African Museum), and one is yet to acquire a repository. Gow (1975) provided the most complete description of the fossil material collected and stored at BPI up to that point, establishing Prolacerta's affinities with archosaurs rather than lizards. Evans (1986) described the braincase in more detail. Modesto and Sues (2004) redescribed the skull as a whole, focusing on the UCMP specimen alongside 5 specimens stored at BPI. The holotype skull in Cambridge was redescribed by Gabriela Sobral (2023).
Antarctic fossils Prolacerta was first reported from Antarctica by Edwin H. Colbert in 1987. The original Antarctic fossils were collected from 1969 to 1971 by James Kitching and his colleagues, working in the Fremouw Formation near the junction of the McGregor and Shackleton glaciers. Colbert described 17 different Prolacerta specimens from Antarctica, all of which are stored at the American Museum of Natural History (AMNH). Most of the AMNH specimens are rather fragmentary, but two nearly complete skulls are included among the sample: AMNH 9520 and AMNH 9521. The Antarctic Prolacerta fossils were amended by Stephan Spiekman (2018), with the description of a new articulated skeleton stored at the Burke Museum of Natural History and Culture (UWBM). This specimen, UWBM 95529, is both the largest and most complete Prolacerta skeleton which has been described, though only fragments of the skull are preserved. The 2018 study re-evaluated Colbert's sample, finding that 14 of the AMNH specimens are still validly referable to Prolacerta. The AMNH fossils are distinctly smaller than the South African remains, and several anatomical differences are apparent. The AMNH fossils tend to have a shorter snout, more conical teeth, dorsal neural spines which are slanted backwards, and a proportionally shorter tibia, among other traits. Colbert preferred the hypothesis that they simply represent juvenile fossils, though he could not disprove the idea that they were from a second species which was smaller than P. broomi. Some of the differences between the AMNH and South African fossils are ambiguous due to quirks of preservation and limited overlap between specimens. UWBM 95529 is not only comparable in size to the South African fossils, but also anatomically indistinguishable from them. This supports the interpretation that the AMNH fossils are juveniles, while dissuading the idea that the Antarctic remains are from a dwarfed species.
Description
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