# Lycosuchus

Lycosuchus ("wolf crocodile") is an extinct genus of carnivorous therocephalian from the Karoo Basin of South Africa that lived roughly 260—258 million years ago, straddling the boundary of the Middle Permian and Late Permian. As a member of the Lycosuchidae, the genus represents one of the earliest diverging therocephalians. The type and only species, L. vanderrieti, is known from a handful of well-preserved specimens preserving the cranium and lower jaw; the holotype US D173 itself, housed at the University of Stellenbosch, South Africa, is a near complete occluded skull and jaws.$^{:322}$ Specimen MB.R. 995, housed at the Museum für Naturkunde Berlin, Germany, consists of a near complete and isolated lower jaw, along with a partial snout and brain case. With the help of μCT data, Pusch et al (2020) described the endocranial anatomy of Lycosuchus vanderrieti. It was a medium-sized predator, reaching 1.2 m (3.8 ft) in length with a skull 23 cm long, typical of early therocephalians. L. vanderrieti bore two functional canines in each maxilla, possibly due to a protracted tooth replacement. Both the upper canines and the single canine of the lower jaw are serrated.
Discovered in South Africa, it was named by paleontologist Robert Broom in 1903 and later assigned by him to Therocephalia.

## History of study
### Discovery and naming

The first known fossil of Lycosuchus, the holotype US D173, was collected and presented to the museum of Victoria College, now known as Stellenbosch University (US), by Reverend van der Merwe prior to the year 1902. The specimen was held there "for some time" before being examined by Scottish-born South African palaeontologist Robert Broom (loaned to him by his colleague at the college Professor van der Riet), who would write a paper describing the fossil and naming it the new genus and species Lycosuchus vanderrieti. This paper was first read at a meeting of the Philosophical Society of South Africa on November 26th 1902 and then formally published by the society in 1903. Notably, Broom did not ascribe any significance to the presence of two pairs of canines and regarded them as comparable to the replacement of milk teeth by the adult pair in modern mammals.
The location where the fossil was originally discovered was only vaguely reported by Rev. van der Merwe as the "Groot Vlakte between Prince Albert, Beaufort West and Willowmore" in the Karoo Basin of South Africa. This area exposes strata from both the Abrahamskraal Formation and the lowest member of the overlying Teekloof Formation (the Poortjie Member), which approximately corresponds to the biozones of the Tapinocephalus Assemblage Zone (AZ) and the lower portion of the Endothiodon AZ. Indeed, the presence of Lycosuchus in the lower part of the latter assemblage zone is so characteristic that it was formally established 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 known range bounded by the known highest and lowest records of subsequently discovered Lycosuchus specimens.
The holotype US D173 is a well preserved and largely complete skull and lower jaws. Indeed, at the time it was one of only a few such completely preserved specimens of carnivorous therapsids from the Karoo, when most others were known and named only from partial fragments of snouts. Broom compared Lycosuchus to similarly complete and well preserved specimens of the cynodont Cynognathus, the gorgonopsian Lycosaurus and fellow therocephalian Ictidosuchus. At the time, our understanding of therapsid relationships was only rudimentary and the systematics and relationships of these forms was only vaguely defined as being grouped together as theriodonts. Broom recognised these forms as representing four distinct subgroups, two primitive (represented by Lycosaurus and Ictidosuchus) and two advanced (represented by Cynognathus and Gomphognathus (a synonym of Diademodon)). Broom identified Lycosuchus as a member of the primitive forms, and although the concept of Therocephalia as it is understood today did not exist yet he made the astute observation that it was in some ways similar to Ictidosuchus than to Lycosaurus, a gorgonopsian. However, in other respects he believed Lycosuchus to retain more primitive features he associated with anomodonts (then including herbivorous dinocephalians), and so considered it to be close to a common ancestor of anomodonts and later theriodonts. He also believed Lycosuchus to be near to the ancestry of the monotremes, which he interpreted as evolving from an ancestor slightly more derived than Lycosuchus but not so far derived as the "advanced" Cynognathus and Gomphognathus (i.e. cynodonts).
That year in April of 1903, Broom redefined Theriodontia to be equivalent to what we would now recognise as Cynodontia, and established the new group Therocephalia for what he previously considered primitive theriodonts (including various modern therocephalians, gorgonopsians and dinocephalians). Shortly after establishing Therocephalia, Broom published a subsequent paper in November 1903 wherein he explicitly identified Lycosuchus as one, although he left its relationships uncertain due to its palate being obscured.

### Early 20th century

The taxonomic significance of the "double canines" of Lycosuchus would not be raised until two consecutive papers published by Broom in May 1908, the first including the descriptions of the therocephalians Trochosuchus and Hyaenasuchus with similar "double canines" to Lycosuchus. In the second paper, Broom regarded these forms as their own "line of descent" amongst early therocephalians, but did not name a family or other subgroup for them. Such a grouping would not be named until 1923 when Baron Franz Nopcsa coined the family Lycosuchidae after Lycosuchus, for which it is typically regarded as the type genus.$^{:510}$ Consequently, the "double-canined" Lycosuchus was often presented as a general representative of lycosuchids, and by extension for early therocephalians as a whole.
Since the discovery of the holotype, additional specimens of Lycosuchus vanderrieti have been recovered from the Tapinocephalus and Endothiodon AZs in the Karoo. In 1952, German palaeontologist Werner Janensch reported on the discovery of the partial skull and mandibles of specimen MB.R.995, although his brief description only focused on superficial details of the lower jaw and he originally only referred the specimen to Lycosuchus sp. MB.R.995 was collected by Janensch in 1929 from Letjesbosch near Beaufort West and later prepared by E. Siegert and J. Schrober, and is housed in the reptile collection of the Museum für Naturkunde (MB.R.) in Berlin, Germany. Two specimens are also housed at the Council for Geoscience (CGS) in Pretoria, South Africa, 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 largely intact and exposed compared to other specimens (despite much of the superficial bones of the snout being badly weathered). This specimen was extensively described by palaeontologist Juri van den Heever in his PhD thesis in 1987 and a later paper in 1994. Another specimen, BP/1/7162 is housed at the Evolutionary Studies Institute (formerly the Bernard Price (BP) Insitute) of the University of the Witwatersrand in Johannesburg, South Africa. Additional specimens at the Evolutionary Studies Institute were each listed by Jennifer Botha and colleagues and Fernando Abdala in 2007 as belonging to Lycosuchus: 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.
CGS M793 is the stratigraphically highest (and therefore the youngest) occurance 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 so are only 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 occurance 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 millon years ago by the International Commission on Stratigraphy as of December 2024.

### 1980s revision to present

In 1980, Juri van den Heever challenged the validity of the "double canine" condition in Lycosuchus (and other lycosuchids), arguing that it simply represented individuals caught during the brief overlap of the alternating functional canine and its replacement at the time of death. This brought into question the taxonomic utility of "double canines" as a lycosuchid characteristic and for their proportions between lycosuchid species, and van den Heever argued the family was an artificial collection of "pristerognathid" (scylacosaurid) specimens undergoing canine replacement.
Subsequently, van den Heever would later revise the entire taxonomy and systematics of early therocephalians in his 1987 PhD thesis, wherein he would recognise only Lycosuchus as the sole valid genus of Lycosuchidae (although also maintaining the family as valid now too). Most other genera were previously only distinguished by variations in tooth count and proportions, and so lacked any clear diagnostic characteristics according to van den Heever and were therefore rendered nomina dubia. However, Hyaenasuchus and Zinnosaurus were complete enough for him to identify traits he considered diagnostic of Lycosuchus vanderrieti and so he concluded they were junior synonyms. Hyaenasuchus had previously only been distinguished from Lycosuchus by a greater tooth count and proportions of the canines, while Zinnosaurus was initially identified as a scylacosaurid ("pristerognathid" at the time) due to only preserving a single pair of canines. Although the taxonomy revision from van den Heever's thesis was never formally published, his conclusions were nonetheless largely adopted by palaeontologists in subsequent work. As the only valid lycosuchid, Lycosuchus became representative of the group as a whole in later studies, most often in phylogenetic analyses of therocephalians.
The synonymy of Hyaenasuchus and Zinnosaurus with Lycosuchus was questioned in 2014 by the re-identification of the therocephalian Simorhinella as a lycosuchid and comparisons with Lycosuchus, prompting a re-examination of other lycosuchid specimens. Lycosuchus and Simorhinella are mostly distinguished by relatively minor differences in the bones of the palate, and these bones are obscured in both Hyaenasuchus and Zinnosaurus. As such, they cannot be told apart from either Lycosuchus or Simorhinella, or identified as specimens of either genus. Consequently, they can no longer be considered synonyms of Lycosuchus and the two genera are now considered nomina dubia.
Recent study of Lycosuchus has centered around its endocranial anatomy from micro-CT analysis of the specimen MB.R.995. This new data has been used to study the internal anatomy of its brain, snout, and teeth, and various studies have shed new light on the anatomy of the inner ear, the maxillary canal and associated trigeminal nerve, and the process of tooth replacement in Lycosuchus, as well as informing phylogenetic analyses that use data on the internal cranial anatomy.

### Other species

Although currently considered monospecific, additional species of Lycosuchus have been proposed by researchers in the 20th century. In his third paper from 1903, Broom named the new species Lycosuchus 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 also 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 Theriodont 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 naming a new species of Lycosuchus in his 1987 thesis, "Lycosuchus keyseri". "L. keyseri" was based upon CCGS 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 incorporating "L. keyseri" was later formally published in 1994, he refrained from naming "L. keyseri" and instead referred to the specimen only 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.