Lycosuchus (meaning "wolf crocodile") 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 South Africa. The type and only species is L. vanderrieti, first described in 1903 by Robert Broom from a nearly complete skull discovered in the Karoo Supergroup. Additional specimens of the same taxon, with a more or less comparable degree of preservation, were later reported, allowing for a better description of the palate and even its internal endocranial anatomy. Two additional species were proposed, but the nature of the fossils on which they are based is considered doubtful. Recognised 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.
Research history
Sometime before 1902, Reverend van der Merwe collected a relatively complete skull from the fossil-bearing deposits of the Karoo Supergroup in South Africa, before donating it to Victoria College in Stellenbosch. Some time later, the specimen was examined in detail by Robert Broom, who described it as representing a new genus and species of theriodont, Lycosuchus vanderrieti. The generic name Lycosuchus is derived from the Ancient Greek λύκος (lýkos, "wolf") and σοῦχος (souchos, "crocodile"), while the specific name vanderrieti honours Professor van der Riet, who loaned the skull to Broom for study. Broom initially described the animal in a paper first read at a meeting of the Philosophical Society of South Africa on November 26th 1902, before it was formally published by the society in 1903. Subsequently, when Victoria College attained university status and became Stellenbosch University, the holotype skull of this taxon was retained there under the catalogue number US D173. The location where the fossil was discovered was only vaguely described by van der Merwe as the "Groot Vlakte between Prince Albert, Beaufort West and Willowmore". This area exposes layers of rock strata from both the Abrahamskraal Formation and the lowest member of the overlying Teekloof Formation (the Poortjie Member), which approximately corresponds to the Tapinocephalus Assemblage Zone (AZ) and the lower portion of the Endothiodon AZ biozones, respectively. Indeed, fossils of Lycosuchus are so characteristic of the base of the latter assemblage that it was formally defined as the Lycosuchus-Eunotosaurus Subzone (SZ) in 2020. Although the exact origin of the holotype from this relatively broad stratigraphic range is not known, it is consistent with the range bounded by the highest and lowest records of subsequent Lycosuchus specimens.
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