Sunday, June 10, 2018

[Paleontology • 2018] Gorynychus masyutinae • A New Therocephalian from the Permian Kotelnich Locality, Kirov Region, Russia

Gorynychus masyutinae
Kammerer​ & Masyutin, 2018

A new therocephalian taxon (Gorynychus masyutinae gen. et sp. nov.) is described based on a nearly complete skull and partial postcranium from the Permian Kotelnich locality of Russia. Gorynychus displays an unusual mixture of primitive (“pristerosaurian”) and derived (eutherocephalian) characters. Primitive features of Gorynychus include extensive dentition on the palatal boss and transverse process of the pterygoid, paired vomers, and a prominent dentary angle; derived features include the absence of the postfrontal. Gorynychus can be distinguished from all other therocephalians by its autapomorphic dental morphology, with roughly denticulated incisors and postcanines. Phylogenetic analysis recovers Gorynychus as a non-lycosuchid, non-scylacosaurid therocephalian situated as sister-taxon to Eutherocephalia. The identification of Gorynychus as the largest predator from Kotelnich indicates that therocephalians acted as apex predators in middle–late Permian transition ecosystems in Russia, corroborating a pattern observed in South African faunas. However, other aspects of the Kotelnich fauna, and Permian Russian tetrapod faunas in general, differ markedly from those of South Africa and suggest that Karoo faunas are not necessarily representative of global patterns.

Figure 1: Holotype of Gorynychus masyutinae. The two blocks (KPM 346 and 347) making up the majority of the holotype shown in articulation. Holotype also includes two incisor teeth (KPM 348 and 349) disarticulated from the skull but found in association (see Figs. 2C and 10D). Scale bar equals 5 cm. Photograph by Christian F. Kammerer.

 Figure 4: Holotype of Gorynychus masyutinae in right lateral view. (A) Photograph and (B) interpretive drawing of skull (KPM 346). Abbreviations: ar, articular; C, upper canine; co, coronoid process of dentary; d, dentary; fr, frontal; i, lower incisor; j, jugal; la, lacrimal; mx, maxilla; na, nasal; pmx, premaxilla; prf, prefrontal; PC, upper postcanine; po, postorbital; q-qj, quadrate-quadratojugal complex; rla, reflected lamina of angular; sa, surangular; smx, septomaxilla; sq, squamosal; ss, squamosal sulcus. Gray coloration indicates matrix, patterning indicates eroded or broken bone surface. Scale bar equals 1 cm. Photograph and drawing by Christian F. Kammerer.

Systematic Paleontology
Synapsida Osborn, 1903
Therapsida Broom, 1905
Therocephalia Broom, 1903

Gorynychus gen. nov.

Type species: Gorynychus masyutinae sp. nov.

Etymology: Named for the legendary Russian dragon Zmey Gorynych (Змей Горыныч), in reference to the fearsome appearance of this taxon and its status as the largest known predator in the Kotelnich assemblage. Also a play on the English word “gory” (meaning bloody) and the Ancient Greek ὄνῠχος (Latinized “onychus,” meaning claw), in reference to this taxon’s inferred behavior being “red in tooth and claw.”

Gorynychus masyutinae sp. nov.

Holotype: KPM 346–349 (Figs. 1–9), a single individual (skull and cervical vertebrae in articulation, pectoral and rib elements disarticulated but directly associated with skull) broken into four pieces: KPM 346, a nearly complete skull (with damaged intertemporal region, occiput, and left temporal arcade) and lower jaws with the anterior 4 1/2 cervicals in articulation; KPM 347, postcranial elements including remaining half of fifth cervical (precise break, originally articulated with anterior portion) and worn sixth and seventh cervicals, ribs, partial clavicle, and left scapulocoracoid impression; KPM 348, isolated but associated incisor with intact crown; and KPM 349, isolated but associated incisor with damaged crown.

Etymology: Named in honor of Olga Masyutina for her skillful preparation of the holotype of this taxon, as well as numerous other important specimens from the Kotelnich locality.

Diagnosis: Therocephalian distinguished from all other members of the group by its autapomorphic dental morphology: all marginal teeth serrated, with serrations forming distinct denticles that are especially prominent on the incisors and postcanines. Postcanines “spade”-shaped and reduced in number (three in the maxilla) relative to most therocephalians. Further distinguished from the other known Russian basal therocephalian Porosteognathus efremovi by a shorter tooth row on the pterygoid transverse process situated on a more discrete, raised boss and an anterolaterally-curved and expanded pterygoid palatal boss with fewer (8–9) teeth (transversely broad with ∼14 teeth in Porosteognathus).

a therocephalian Gorynychus masyutinae, an apex predator during the mid-Permian, treeing a small herbivore, Suminia getmanovi.
Illustration: Matt Celeskey  

Based on a nearly-complete skull and partial skeleton and two additional, fragmentary specimens, a new therocephalian taxon, Gorynychus masyutinae, is described from the (probably) earliest late Permian Kotelnich locality of Russia. Gorynychus is the largest known predatory tetrapod in the Kotelnich assemblage, and demonstrates that therocephalians acted as top predators in Russian as well as South African assemblages during the transition between typical middle and late Permian terrestrial communities. Although falling outside of Eutherocephalia, Gorynychus is more closely related to eutherocephalians than to the large-bodied therocephalian predators of southern Africa (and possibly earlier Permian assemblages in Russia, if Porosteognathus from the middle Permian Isheevo fauna truly is a scylacosaurid). The Kotelnich therocephalian fauna shows greater diversity of eutherocephalians than probable coeval faunas in South Africa, and suggests that initial diversification in this clade probably was not occurring in the Karoo Basin.

Christian F. Kammerer​ and Vladimir Masyutin. 2018. A New Therocephalian (Gorynychus masyutinae gen. et sp. nov.) from the Permian Kotelnich Locality, Kirov Region, Russia. PeerJ. 6:e4933. DOI: 10.7717/peerj.4933