Prolacerta broomi

Prolacerta broomi is an Early Triassic archosauromorph known from South Africa and Antarctica. Its name once encouraged comparisons with lizards, but modern analyses place it on the archosauromorph branch, outside true lizards. The Cambridge holotype is a compressed skull and lower jaws; a larger Antarctic specimen preserves much of the postcranial skeleton. In 2023, micro-CT scanning of the type corrected earlier bone identifications and exposed structures hidden inside the fossil. The animal's history shows why its anatomy remains an active subject in the other fossil reptile catalogue.

Quick facts

The name and its type specimen

Francis R. Parrington named Prolacerta broomi in 1935 from a small, partly disarticulated skull found at Harrismith Commonage in South Africa. The holotype, UCMZ 2003.41R, includes most of the skull and the lower jaws, but compression obscures some contacts between bones. Early comparisons with lizards reflected the questions palaeontologists were asking at the time. The genus name is historical; it does not mean that this animal was a lizard or the ancestor of modern lizards.

Additional fossils accumulated from the Karoo Basin, and later work recognised related specimens in Antarctica. This expanded sample improved knowledge of the trunk and limbs, but created a practical issue: many referred skeletons preserve body anatomy better than the type, while the type preserves a more complete skull. To diagnose a species consistently, comparisons must connect the two kinds of evidence without assuming every referred specimen belongs to one taxon.

A larger Antarctic skeleton and a Gondwanan range

Stephan Spiekman's 2018 description of UWBM 95529 from the lower Fremouw Formation reported the largest Prolacerta specimen described at that time. It is nearly articulated and preserves a nearly complete postcranium as well as four skull elements. Comparison with South African fossils revealed no clear characters separating the Antarctic material, supporting its assignment to P. broomi.

The specimen helped revise features of the premaxilla, hand and pelvic girdle. It also provides a valuable point of comparison across southern Gondwana. The conclusion is that currently known Antarctic material fits the South African species, not that every similar Early Triassic bone from the continent must belong to it. A distribution across two regions is supported by identifiable fossils; a precise dispersal route is not.

Micro-CT changed the reading of the holotype

In 2023, Gabriela Sobral revisited the holotype using micro-computed tomography. The scan corrected the identification of some elements, including the left prefrontal and lacrimal, and revealed bones that were not visible in the earlier description: parts of the palate, lower jaw and braincase. The lacrimal contributes to the dorsal alveolar canal, a detail that would be easy to miss if the type were understood only from its exposed surface.

That study also entered the holotype as a separate operational unit in phylogenetic analyses. In those tests, the type did not group consistently with all referred Prolacerta specimens, and some runs placed it more basally than expected. This points to possible inconsistency in the material currently assigned to the species. It is a prompt for further revision, not proof that the named species must immediately be split.

What the teeth and limbs imply

The teeth are recurved and suited to gripping food. A small predator is a plausible interpretation of the jaws and body plan, but no stomach contents identify prey. The fossils establish bone shape, not a menu. Likewise, the long tail and limb bones inform proportions, but they do not preserve a trackway or a measured running speed.

Classification has moved away from the old lizard comparison. Current work treats Prolacerta as an early-diverging archosauromorph, a member of the broader branch that includes archosaurs, although its exact position relative to other stem forms can vary with the analysis. Comparisons with other early diapsids help test these relationships; superficial resemblance is not enough to establish direct ancestry.

A profile still being refined

The strongest account combines a name-bearing skull, a growing set of South African fossils, a large Antarctic postcranium and new internal views from scanning. These records do not all contribute the same information. The holotype anchors the name, the Antarctic skeleton clarifies body anatomy, and CT helps check whether referred skulls have been interpreted consistently.

Prolacerta broomi is therefore both a familiar Early Triassic reptile and a useful caution about taxonomic certainty. Its body proportions and many skull bones are documented, while the unity of every referred specimen remains open to testing. Colour, skin, social behaviour and exact diet are not preserved. The new scan matters because it gives future comparisons a more complete description of the actual type.