Adult morphology of the therocephalian Simorhinella baini from the middle Permian of South Africa and the taxonomy, paleobiogeography, and temporal distribution of the Lycosuchidae

Abstract

The Middle Permian tetrapod fauna of the South African Beaufort Group is taxonomically diverse and includes representatives of all major therapsid groups, including the earliest records of Eutheriodontia. In the Middle Permian, eutheriodonts are represented mainly by large therocephalians, which made up a large proportion of the vertebrate predators in these faunas. Here we describe the skull and partial skeleton of a large therocephalian from the uppermost Tapinocephalus Assemblage Zone (AZ) of South Africa. A combination of features, including the short snout, presence of three to four upper postcanines and presence of teeth on the pterygoid processes, indicates that the new specimen belongs to the earliest-diverging therocephalian family, Lycosuchidae. The presence of a well-developed midline ridge on the ventral surface of the vomer indicates that the new specimen can be referred to Simorhinella baini, a species previously represented only by a tiny juvenile skull. The new specimen forms the basis for a taxonomic re-evaluation of the Lycosuchidae as well as of the geographic and stratigraphic range of the family. We recognize two valid species within the Lycosuchidae: the type species Lycosuchus vanderrieti represented by five specimens and Simorhinella baini represented by two specimens, with an additional 22 specimens currently identifiable as Lycosuchidae incertae sedis. Lycosuchid specimens range throughout the Tapinocephalus and Pristerognathus AZs; specimens of Simorhinella are restricted to the Tapinocephalus AZ, whereas Lycosuchus specimens are documented in both the Tapinocephalus and Pristerognathus AZs.

New information on the morphology and stratigraphic range of the mid‐Permian gorgonopsian Eriphostoma microdon Broom, 1911

“…Gorgonopsians are one of the rarest faunal components of the Tapinocephalus AZ, with the dominant predators of the time being lycosuchid and scylacosaurid therocephalians and the common dinocephalian Anteosaurus magnificus (Boonstra ; Kammerer ; Abdala et al . ). Historically, Tapinocephalus AZ gorgonopsians were referred to a number of different genera and species, the first‐named of which is Eriphostoma microdon Broom, .…”

Novel Endocranial Data on the Early Therocephalian Lycosuchus vanderrieti Underpin High Character Variability in Early Theriodont Evolution

“…Despite their abundance, these early therocephalian taxa have received little study relative to their later Permo-Triassic relatives. Two families of early therocephalians are current recognized (Scylacosauridae and Lycosuchidae), both consisting of large-bodied (1-3 m body length) predators (van den Heever, 1994;Abdala et al, 2014a). Scylacosaurids exhibit long, comparably narrow snouts and include the oldest known therocephalians (both taxa reported from the Eodicynodon AZ are scylacosaurids; Abdala et al, 2008).…”

“…Scylacosaurids exhibit long, comparably narrow snouts and include the oldest known therocephalians (both taxa reported from the Eodicynodon AZ are scylacosaurids; Abdala et al, 2008). By contrast, lycosuchids are characterized by relatively short, broad snouts and reduction of the postcanine dentition (van den Heever, 1994;Abdala et al, 2008Abdala et al, , 2014a. Abdala et al (2014a) recently described new lycosuchid specimens and reviewed the family's taxonomy, recognizing only two valid species: Lycosuchus vanderrieti and Simorhinella baini.…”

“…By contrast, lycosuchids are characterized by relatively short, broad snouts and reduction of the postcanine dentition (van den Heever, 1994;Abdala et al, 2008Abdala et al, , 2014a. Abdala et al (2014a) recently described new lycosuchid specimens and reviewed the family's taxonomy, recognizing only two valid species: Lycosuchus vanderrieti and Simorhinella baini. Simorhinella is restricted to the Tapinocephalus AZ, whereas Lycosuchus ranges from the uppermost Tapinocephalus AZ through the Pristerognathus AZ.…”

“…The position of Simorhinella is less certain, and it has generally been excluded from phylogenetic analyses of Therocephalia. Abdala et al (2014a) noted that Simorhinella shares some features with scylacosaurids to the exclusion of Lycosuchus (e.g., presence of a median vomerine crest, ventral extension of ridges from the transverse processes of the pterygoid), suggesting that Lycosuchidae may be paraphyletic. More recently, Liu and Abdala (2019) recovered Gorynychus masyutinae, a Russian taxon originally found to be the sister-taxon of Eutherocephalia (Kammerer and Masyutin, 2018), as the sister taxon of Lycosuchus.…”