Proterosuchus fergusi

Proterosuchus fergusi is a basal archosauriform from the Early Triassic, known for its appearance shortly after the great Permian–Triassic extinction, approximately 252 million years ago. Its fossils have been found in the Katberg Formation of the Beaufort Group (South Africa), specifically in the Lystrosaurus biostratigraphic zone, one of the earliest of the Triassic. The first specimen was described by Broom in 1903, but due to the poor preservation of the holotype, a neotype (RC 846) was proposed and accepted by Ezcurra and Butler in 2015.

Morphologically , Proterosuchus had a long, low skull with a noticeably downward-curved snout, the result of an elongated premaxilla that projected beyond the lower jaw. This structure is one of its most distinctive features and has been the subject of various functional interpretations, from defense to prey manipulation. The skull could reach up to 50 cm in length, suggesting that adult animals could measure between 2.5 and 3.5 meters in total length.

The dentition was ziphodont: the teeth were curved backward, laterally compressed, and had serrated edges. There were between 7 and 9 premaxillary teeth, and up to 30 in the maxilla per side. This indicates that it was an active predator, probably a generalist, capable of capturing medium- to small-sized prey, possibly including amphibians and small synapsids.

In terms of its evolutionary position , Proterosuchus fergusi is considered one of the most basal archosauriforms, lying at the base of the radiation that gave rise to later forms such as Erythrosuchus and eventually to the true archosaurs (including dinosaurs, pterosaurs, and crocodiles). Its intermediate morphology between primitive diapsids and advanced archosaurs has been key to understanding the early origin of this group.

Recent studies of bone histology and cranial development (Botha-Brink & Smith, 2011; Ezcurra & Butler, 2015) have shown that Proterosuchus grew rapidly during the early stages of its life, with a skeleton that modified significantly throughout its ontogeny. In juvenile specimens, for example, the curved snout is less developed, and the number of teeth is proportionally fewer, while in adults the nasal curvature is accentuated and the skull becomes proportionally taller.

Functionally, Proterosuchus has long been interpreted as a semiaquatic animal, based on the position of its nostrils, the general shape of its skull, and its comparison with modern crocodiles. However, CT scans of the endocranium (Brown et al., 2020) revealed an inner ear with semicircular canals oriented in a way that suggests a slightly elevated head posture, and a brain with structures compatible with a more terrestrial lifestyle. The long, specialized cochlear canal would also indicate hearing sensitivity at low frequencies, which may have been useful for detecting prey or predators.

Although there is no complete monograph on the skeleton of Proterosuchus fergusi , numerous authors have described various aspects of its anatomy, including the skull, vertebrae, shoulder girdle, and pelvis. Its locomotion is interpreted as quadrupedal, with well-developed limbs and a somewhat extended but higher stance than in more primitive reptiles, which would have allowed it to move efficiently both on land and, possibly, in humid environments or near bodies of water.

Approximate measurements of Proterosuchus:

• Scale 1:20 Complete
• Length 97 mm
• Height 27 mm
• Width 66 mm
• Snout-tail length 175 mm