Lycosuchus

Lycosuchus is a genus of early therocephalian (an extinct type of therapsid, the group that modern mammals belong to) that lived roughly 260–258 million years ago, straddling the boundary of the Middle and Late Permian period, from what is now the Karoo Basin of South Africa. The type and only species is L. vanderrieti, named by paleontologist Robert Broom in 1903. Lycosuchus is known from a handful of well-preserved specimens mostly preserving the skull and lower jaw; the holotype specimen itself being a nearly complete and undistorted occluded skull and jaws. Other specimens have revealed more details of the palate and even its internal endocranial anatomy. Lycosuchus fossils are known from the uppermost Abrahamskraal and lowest Teekloof Formations, corresponding to the Tapinocephalus and Endothiodon faunal assemblage zones.

With a skull ranging from 23 cm (9.1 in) to almost 30 cm (12 in) long, Lycosuchus was a large therocephalian but still relatively mid-size compared to some other early therocephalians. Like other early therocephalians, it resembles a gorgonopsian with large incisors and its sabre-like canines, though its snout is relatively shorter and broader than other early therocephalians, with even fewer teeth behind the canines. Historically, Lycosuchus was thought to bear not one but two pairs of functioning canines in its upper jaws, unlike other therapsids. However, it has since been recognised that the two pairs instead represent the overlap of alternating replacement teeth (the pattern seen in other predatory therapsids), caught in fossilisation as one pair replaced the other. However, the pattern of replacement still seems to be unusual in Lycosuchus, as overlap between both pairs occurs much more frequently compared to typical therapsids (where this condition is rarely preserved).

Lycosuchus forms the basis of the family Lycosuchidae and is a distinct lineage from most other early therocephalians (most of which belong to the family Scylacosauridae). It is one of the earliest evolutionarily branching members of Therocephalia, a group of stem mammals with a diverse range of anatomy and diets. Early therocephalians were typically large carnivores, exemplified by Lycosuchus with its gorgonopsian-like teeth and a relatively robust snout and jaws, more so than other early therocephalians. Lycosuchus survived a mass extinction at the end of the Middle Permian that saw the extinction of most other large therocephalians (including its close relative Simorhinella and most scylacosaurids), as well as larger therapsid carnivores like Anteosaurus. Lycosuchus is the last known lycosuchid in the fossil record, and it may have competed with large gorgonopsians (such as Gorgonops) as the ecosystem recovered before it went extinct.