Lycosuchus

skull of L.vanderrieti from his first 1903 description 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. 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. 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. 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. 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). 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. 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. 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==

of Lycosuchus in life with exposed canines and hypothetical hair 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. Teeth The upper dentition of Lycosuchus consistently include only five incisors in each premaxilla, a pair of large canines, and only few much smaller postcanines (varying between two or three). All the teeth are sharp and serrated on both their front and rear edges. though replacement canines co-occur with the functional predecessor much more often in lycosuchids than in other therapsids. The complete internal anatomy of the nerves in the snout was only realised through CT-scanning of specimen MB.R.995 in the 21st century. The maxillary canal begins just behind the canines, with a pair of alveolar nerves branching off towards the teeth. The region of the canal ahead of this point (homologous to the infraorbital nerve in modern mammals) then splits into three main branches (rami), two narial rami (external and internal) and a labial ramus, with each splitting into further branching arrays of nerves. The external nasal ramus is notable for its unusually vertical orientation, and it is highly ramified into numerous radiating branches. The latter trait is primitive to both therocephalians and cynodonts, with the nerve being shorter and less ramified in derived members of each clade. The bony labyrinth of the inner ear is unusual, as the longest of the three semicircular canals is the lateral canal, followed by the anterior (front), and the smaller posterior canal. The anterior canal is usually the longest in therapsids (and most other terrestrial vertebrates), and among fossil therapsids a long lateral canal has only also been reported in the burrowing dicynodont Kawingasaurus. Lycosuchus also has a cochlear recess, a precursor to the elongated, coiled cochlea of modern mammals. A cochlear recess is typical of cynodonts but not of most other therocephalians and even most other therapsids. Indeed, the only other therocephalian identified with a cochlear recess is the derived baurioid Microgomphodon, and it is known to be absent in other eutherocephalians. ==Classification==

When Broom described Lycosuchus in 1903, the taxonomy of "mammal-like reptiles" was rudimentary at the time. The genus was therefore placed rather imprecisely within Theriodontia, alongside forms such as Cynognathus, Lycosaurus, and Ictidosuchus. Broom recognised four distinct subgroups, divisible into two primitive subgroups (represented by Lycosaurus and Ictidosuchus) and two advanced (represented by Cynognathus and Gomphognathus). He identified Lycosuchus as a member of the primitive forms, while noting that it shows closer affinities to Ictidosuchus than to Lycosaurus. However, in other respects he believed Lycosuchus to retain more primitive features he associated with anomodonts, and so considered it to be close to a common ancestor of anomodonts and later theriodonts. Broom further suggested that Lycosuchus lay close to the ancestry of monotremes, which he interpreted as having evolved from an ancestor slightly more derived than Lycosuchus, but less advanced than "advanced" forms such as Cynognathus and Gomphognathus. Broom redefined Theriodontia for the advanced forms, and created the new group Therocephalia for what he had considered the primitive theriodonts. Shortly after erecting this group, he published a follow-up paper in November of the same year in which he explicitly identified Lycosuchus as a therocephalian, albeit of uncertain relationships due to being unable to examine the holotype's palate. In 1905, Broom ultimately grouped all of these "mammal-like reptiles" into a new clade that he named Therapsida. While initially attaching no particular importance to the "double canines" in Lycosuchus, comparing them instead to the replacement of milk teeth in modern mammals, In the second paper, Broom regarded these three genera 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, which it is the type genus. Consequently, the "double-canined" Lycosuchus was often presented as representative of both lycosuchids and early therocephalians as a whole. In 1980, van den Heever challenged the validity of the "double canines" of the lycosuchids, arguing that they simply represented individuals of typical early therocephalians 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 supposed differing proportions between lycosuchid species, and van den Heever argued the family was an artificial collection of "pristerognathid" (scylacosaurid) therocephalians simply undergoing canine replacement. Subsequently, van den Heever would later revise the entire taxonomy and systematics of early therocephalians in his 1987 PhD thesis, reinstating Lycosuchidae but recognising only Lycosuchus as the sole valid member. Most other lycosuchids 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 of it. In a 2014 study, Fernando Abdala and colleagues questionned the synonymy of Hyaenasuchus and Zinnosaurus with Lycosuchus, following the reidentification of the therocephalian Simorhinella as a lycosuchid, prompting a re-examination of most other specimens of this group. Lycosuchus and Simorhinella are distinguished only by minor differences in the bones of the palate, but as these elements are obscured in the type specimens of Hyaenasuchus and Zinnosaurus, the authors consider it impossible to determine whether they might belong to either of these genera or another. Consequently, they are no longer regarded as synonyms of Lycosuchus and are now considered as nomina dubia. although the latter is not typically considered a lycosuchid. This result is not common though, and Gorynychus is more often found in a more derived position closer to scylacosaurids. All cladograms below are simplified to focus on the relationships of Lycosuchus and early therocephalians, and relationships within bolded terminal clades are not shown. A novel result was recovered by Pusch et al. (2024) from an analysis focused on the relationships of early cynodonts. Using a dataset with much more endocranial data than previous studies, they found Lycosuchus and Alopecognathus (representing Scylacosauridae) to be sister taxa in a clade that itself was the sister of another clade made by Eutherocephalia and Cynodontia, rendering Therocephalia paraphyletic. However, this analysis only included four therocephalians, with only Olivierosuchus and Theriognathus representing Eutherocephalia. A simplified cladogram of these results is shown below. }} ==Palaeobiology==

The serrated teeth of Lycosuchus indicate it had a carnivorous diet. Its dentition is similar to that of gorgonopsians, being dominated by large canines and with only a few weak postcanines. Its proportionately shorter and more rounded snout has been proposed to both possess more torsional strength (i.e be more resistant to twisting) and could perhaps bite with greater force at the canine compared to scylacosaurids. Broom initially speculated that the supposed two pairs of canines were specialised for different functions, based on the rear pair being more robust and having serrations only on the rear edge, while the anterior pair had them on both. In Lycosuchus and its relatives, this was thought to be a retention of the primitive condition seen in earlier sphenacodont synapsids like Dimetrodon. It has since been recognised that the "double canines" are a product of the pattern of tooth replacement in predatory therapsids (including gorgonopsians, scylacosaurids, and cynodonts). Canine replacement in Lycosuchus broadly follows the same pattern seen in other theriodonts, with the canine alternating between an anterior and posterior alveolus with every replacement. In other predatory therapsids, only one erupted canine is typically present at a time, and the interval of overlap between the alternates is brief. In Lycosuchus, however, the functional canine and its replacement co-occur much more often. Indeed, CT-scanning of MB.R.995 reveals that as a replacement is erupting in the alternate alveolus a direct replacement for the old canine in the original alveolus is already developing before it has even been lost. The nature of this overlap is not resolved, and different hypotheses have put forward to explain it. In 2014, Abdala and colleagues proposed that Lycosuchus and other lycosuchids may have experienced a much more rapid rate of canine replacement than other therapsids. By replacing the canines more frequently, there are more instances in their lifespan of overlap between pairs than in other therapsids and explaining why they are preserved this way more often. From the CT data of MB.R.995, Pusch and colleagues proposed a contrasting hypothesis in 2020. They suggested that Lycosuchus may have had a more protracted development for its canines, with the older functional pair remaining in place long into the development of the alternate pair, to the point that its direct replacement in the same alveolus begins forming before it is finally lost. While the notion that Lycosuchus had two independentantly functional sets of canines has been correctly dismissed, Pusch and colleagues suggested that the co-occurring canines in each maxilla may still both have been "functional" at the same time. In other predatory therapsids, the older worn canine falls out before it is functionally replaced by its alternate, so that only a single canine in each upper jaw is functioning at a given time. While second pair of canines in Lycosuchus represent the alternate replacements of the older pair, both pairs were presumably both "functional" while they were both erupted and co-occurring, at least to a degree. The purpose of this arrangement is less clear, as van den Heever argued in 1980 that two closely packed canines acting as a single unit would impede the efficiency to both penetrate and tear flesh due to their bulk and by obscuring their serrations. ==Palaeoecology==

Palaeoenvironment Lycosuchus is notable amongst the fossil therapsids of the Karoo basin as it is known from two distinct assemblage zones (AZs), living at the end of the Tapinocephalus AZ and crossing into the Endothiodon AZ. The interval of time across the Capitanian mass extinction has been argued to be marked by increasing environmental aridity from the Tapinocephalus AZ into the Endothiodon AZ in the Karoo, although average temperatures seem to have remained much the same. The depositional environment of the Karoo Basin at this time was a gently sloping alluvial plain made up of high-energy braided rivers and their surrounding floodplains that drained north to south from the Gondwanide mountains (represented in South Africa today by the Cape Fold Mountains) into the Ecca sea to the northeast, a receding inland sea. Although the early Endothiodon AZ was relatively drier, the floodplains were still well-vegetated. This period also saw an increase in river flow due to tectonic uplift of the Gondwanides, carrying and depositing much more sand through the channels and on the plains. This uplift was also associated with more volcanic activity that occasionally covered the alluvial plains in ash fall. Nine genera of large herbivorous tapinocephalian dinocephalians are known to overlap at least the lowest range of Lycosuchus; namely the tapinocephalids Agnosaurus, Criocephalosaurus, Mormosaurus, Moschognathus, Moschops, and Tapinocephalus, the two titanosuchids Jonkeria and Titanosuchus, as well as Styracocephalus. Other large herbivores are the bradysaurians, basal pareiasaurs, namely Bradysaurus, Embrithosaurus, and Nochelesaurus. The roles of medium-sized to small herbivores were occupied mostly by anomodonts, including the diminutive "dromasaurs" Galechirus, Galepus and Galeops, as well as a variety of dicynodonts such as Brachyprosopus, Emydops, Pristerodon and the smaller pylaecephalids Diictodon, Eosimops, Prosictodon and Robertia. There were also some small reptiles, such as the millerettid Broomia, procolophonomorph Australothyris, and the enigmatic Eunotosaurus. Most of these genera were wiped out during the Capitanian mass extinction event, the main pulse of which occurred roughly 260 million years ago. This saw the disappearance of all dinocephalians and pareiasaurs in the Karoo, as well as many of the other mid to large early therocephalians. Following the extinction pulse, the Tapinocephalus AZ fauna was reduced to only a few surviving genera, including Lycosuchus along with the scylacosaurids Alopecognathus and Pristerognathus, the small dicynodonts Diictodon, Emydops and Pristerodon, and Eunotosaurus. This reduced, low-diversity survivor fauna represents the end of the Tapinocephalus AZ. With the extinction of Anteosaurus, Lycosuchus and other early therocephalians now occupied the role of top predators. It is unclear why some large early therocephalians survived while others perished in the extinction, even between close relatives like Lycosuchus and Simorhinella, suggesting that body size alone was not a main factor. Despite the drop in diversity, therocephalian fossils remain relatively abundant in this low-diversity zone, suggesting that one or more of the surviving genera, perhaps Lycosuchus, actually increased in abundance following the extinction. Endothiodon Assemblage Zone The beginning of the subsequent assemblage zone fauna and the onset of ecosystem recovery is marked by the appearance of the mid-sized dicynodont Endothiodon. Other new additions to the surviving fauna are the gorgonopsians Gorgonops and later Aelurosaurus, potentially the rare scylacosaurid Hyorhynchus (the only novel early therocephalian taxon in this assemblage zone, if it is also not a survivor of the Tapinocephalus AZ), the hofmeyriid therocephalians Hofmeyria and Ictidostoma, the baurioids Ictidosuchoides and Ictidosuchops, as well as the dicynodont Dicynodontoides and possibly the biarmosuchian Lobalopex. This fauna comprise the Lycosuchus-Eunotosaurus Subzone, which shows a mix of survivors of the older Guadalupian Tapinocephalus AZ like Lycosuchus with the onset of typical Lopingian dicynodont-dominated fauna. Despite surviving a mass extinction, the presence of Lycosuchus (and other survivors) in this subzone is regarded as an example of a "dead clade walking", where the final extinction of a lineage is delayed for some time after the initial pulse of an extinction event. The surviving species, including Lycosuchus, are rarer than they were in the preceding Tapinocephalus AZ (with the exception of the gorgonopsian Eriphostoma), and Lycosuchus may have competed with larger gorgonopsians like Gorgonops as predators in the new ecosystem. The extinction of Lycosuchus and its disappearance from the fossil record marks the end of the Lycosuchus-Eunotosaurus SZ, and marks a secondary extinction pulse that wiped out most of the remaining genera from the Guadalupian along with it. ==See also==