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 to almost 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 (lýkos, "wolf") and (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.
Following the description of the holotype, additional specimens of L. vanderrieti were discovered in the Karoo Supergroup, bringing the total number of currently recognized fossils to five. In 1929, Werner Janensch discovered at Letjesbosch, near Beaufort West, an incomplete skull consisting of an isolated but nearly complete lower jaw, associated with a portion of the snout and a braincase. He assigned it to Lycosuchus sp. in his 1952 brief description. This specimen is now housed under the number MB.R.995 in the fossil reptile collections of the Museum für Naturkunde, Berlin, Germany, and has been subsequently reassigned to the type species in the few later studies in which it is mentioned. It was ultimately described in detail in two studies led by Luisa C. Pusch, published in 2020 and 2024. Using micro-CT scans on this material, these studies have made it possible to examine the internal anatomy of the brain, snout, and dentition, providing new insights into the structure of the inner ear, the innervation of the snout, and the process of tooth replacement, while also enhancing phylogenetic analyses through the inclusion of characters derived from internal cranial anatomy.
Two specimens are housed at the Council for Geoscience in Pretoria, South Africa, under the numbers CGS MJF 68 and CGS M793. The latter, discovered by A. Chuma, has been regarded as one of the best preserved specimens of Lycosuchus, with the bones of the palate and braincase being mostly intact and better exposed compared to other specimens (though the superficial bones of the snout are badly weathered). This specimen was extensively described by Jurgens van den Heever in his 1987 PhD thesis, and in a later paper published in 1994. The largest known specimen of Lycosuchus is housed at the Evolutionary Studies Institute (formerly the Bernard Price Institute) of the University of the Witwatersrand in Johannesburg, under the catalogue number BP/1/7162. Other specimens of Lycosuchus at the Evolutionary Studies Institute were listed by both Jennifer Botha and colleagues and Fernando Abdala in 2007: BP/1/276, BP/1/499, BP/1/1100 and BP/1/1768. However, of these specimens BP/1/276 and 1768 have since been identified as Pristerognathus and BP/1/1000 as Glanosuchus instead, and none are recognised as Lycosuchus.
CGS M793 is the stratigraphically highest (and therefore the youngest) occurrence of Lycosuchus in the fossil record, coming from the Drie Kop 396 farm in the uppermost Poortjie Member (uppermost Lycosuchus-Eunotosaurus SZ of the Endothiodon AZ). By contrast, the stratigraphically lowest specimens are CGS MJF 68 and BP/1/7162. The former was discovered on the Uitzigt 171 farm to the north of Victoria West in the uppermost Abrahamskraal Formation. BP/1/7162 was discovered on the Hilary farm in Jansenville of the Eastern Cape Province. Historically, the equivalent strata from the Eastern Cape was regarded as a separate formation, the Koonap Formation, but it has recently been incorporated into the Abrahamskraal Formation. Both localities correspond to the uppermost Tapinocephalus AZ, defined as the Diictodon-Styracocephalus SZ. These lowest localities are stratigraphically close to the boundary of—and therefore can only be slightly older than—the Capitanian mass extinction event between the Abrahamskraal and Teekloof formations, which is radiometrically dated to approximately 260.259 ± 0.081 million years ago. The upper boundary of the Eunotosaurus-Lycosuchus SZ—and so the last occurrence of Lycosuchus—is less precisely constrained, but is thought to be between 259 and 258 million years ago. This range therefore also crosses the Guadalupian/Lopingian boundary (i.e. from the middle to the late Permian), which is accepted as 259.51 ± 0.21 million years ago by the International Commission on Stratigraphy as of December 2024.
Proposed and formerly classified species
Although currently considered monospecific, additional species of Lycosuchus were proposed by researchers in the 20th century. In his third paper from 1903, Broom named the new species L. mackayi from a poorly preserved maxilla discovered some years earlier by Mr. G. Mackay. Broom assigned the specimen to Lycosuchus based on a similar pattern of dentition to the holotype (two concurrent canines and a single small postcanine), but justified erecting a second species due to it being larger than the holotype of L. vanderrieti yet presumed to be less mature. This was based on the second (and the assumed permanent) canine being smaller (i.e. from a younger animal) in this specimen, which has since been recognised as a typical part of the alternating theriodont canine replacement pattern and not indicative of age. The specimen otherwise lacks diagnostic features and so L. mackayi is now regarded as a nomen dubium. The specimen itself was re-identified only as Theriodontia incertae sedis at first by van Den Heever in 1987. However, as it comes from a stratigraphic position above the range of large early therocephalians (based on the specimen's direct association with a specimen of the dicynodont Oudenodon) and because the postcanine is tilted back somewhat, it most likely belongs to a gorgonopsian.
Van den Heever himself also proposed a new species of Lycosuchus in his 1987 thesis, "L. keyseri". This taxon was based upon CGS C60, a partial snout and dentary collected by and proposed to be named after Dr. Andre W. Keyser. CGS C60 is well preserved, including much of the internal anatomy of the skull, and it contributed extensively to van den Heever's description of lycosuchid skull anatomy. He proposed that it belonged to a new species owing to the absence of a ventral maxillary flange that he considered diagnostic for L. vanderrieti. However, when the descriptive part of his thesis based upon CGS C60 was later formally published in 1994, he refrained from naming "L. keyseri" and instead only referred to the specimen as a lycosuchid. Consequently, "L. keyseri" was never established as a valid species and so the name is a nomen nudum. The specimen itself is currently considered to be Lycosuchidae incertae sedis.
Description
Lycosuchus is a large therocephalian, with the holotype skull measuring long and the largest measured skull BP/1/7162 at long. This is relatively mid-sized compared to other lycosuchids, however, and it is surpassed in size by several other lycosuchid specimens, including a mature Simorhinella at long.