The postcranial anatomy of Moschorhinus kitchingi (Therapsida: Therocephalia) from the Karoo Basin of South Africa

Material

The following description is based on previously collected and undescribed specimens referred to Moschorhinus (Table 1). All of the specimens facilitating the following description include well-preserved cranial material that were previously used in Huttenlocker & Botha-Brink (2013) enabling the positive referral of specimens to Moschorhinus. All the specimens selected for this description are housed in the Karoo fossil collections of South Africa and were collected from the upper Permian Daptocephalus AZ and Lower Triassic Lystrosaurus declivis AZ of the Karoo Basin of South Africa. All the material described in this study was personally examined, measured, and photographed by the authors. Measurements of the material were taken using Mitutoyo digimatic calipers and digital photographs were taken using a Canon 800D camera body equipped with 18–55 and 55–250 mm lenses at varying focal lengths.

Anatomical terminology and conventions

Previous authors have described discrete regions (i.e., cervical, thoracic, and lumbar) of the presacral axial skeleton of therocephalians (e.g., Watson, 1931; Attridge, 1956; Brink, 1958b; Cys, 1967; Cluver, 1969; Kemp, 1986; Fourie & Rubidge, 2007, 2009; Botha-Brink & Modesto, 2011; Sigurdsen et al., 2012; Fourie, 2013). The recent quantitative study of Jones et al. (2018) on the evolution of the specialized and regionalized axial skeleton of mammals suggests this only occurred at the crown mammal radiation in the synapsid lineage and that the presacral region of the therapsid skeleton is comprised of cervical and dorsal (anterior and posterior) units. Following this, we therefore opt to make use of cervical, anterior dorsal, mid-dorsal, posterior dorsal, and refer to specific vertebrae and ribs to highlight salient features for the description of the axial material of Moschorhinus.

Historically and more recently, previous authors have described the humerus and femur as extending out laterally and parallel to the ground so that they display dorsal, ventral, anterior, and posterior surfaces (e.g., Haughton, 1929; Boonstra, 1964; Kemp, 1978, 1986; Fourie & Rubidge, 2007, 2009), following the anatomical conventions used for sprawling animals such as non-therapsid synapsids (e.g., Romer & Price, 1940; Romer, 1956; Hopson, 2012). At least some therapsids are thought to have adopted a dual gait stance, with a sprawled forelimb and a semi-erect or erect hind limb in contrast with the sprawled fore- and hind limbs of the more basal non-therapsid synapsids (Kemp, 1978; Blob, 2001). Moreover, some therocephalians have been interpreted as having a facultatively erect hind limb posture capable of variable gaits (Kemp, 1978). Based on the morphology of the glenoid of Moschorhinus we describe the humerus as extending posterolaterally from the glenoid and parallel to the ground so that it presents with a dorsal, ventral, lateral, and medial surface. On the other hand, we interpret the femur as being held more closely to the sagittal plane so that it presents with an anterior, posterior, lateral, and medial surface. These anatomical directions are used in the following descriptions for the forelimb and hind limb, respectively.

Systematic palaeontology

THERAPSIDA Broom, 1905

EUTHERIODONTIA Hopson & Barghusen, 1986

THEROCEPHALIA Broom, 1903

AKIDNOGNATHIDAE von Nopsca, 1928

MOSCHORHINUS Broom, 1920

MOSCHORHINUS KITCHINGI Broom, 1920

Tigrisuchus simus Owen, 1876

‘Scymnosaurus’ warreni Broom, 1907

Moschorhinus warreni (Broom, 1932)

Moschorhinus minor Broom, 1936

Moschorhinus esterhuyseni Broom, 1940

Moschorhinus natalensis Brink, 1958a

Holotype—NHMUK R5698, an incomplete skull missing the posterior end.

Type locality—NHMUK R5698 was collected by James William Kitching (1896–1953) (uncle of prolific fossil collector James William Kitching (1922–2003)) near the Bethesda Road in Graaff-Reinet, Eastern Cape Province, Republic of South Africa. The original stratigraphic provenance was documented as “Cistecephalus zone” of the Karoo Basin.

Occurrence—Occurs in the Lystrosaurus maccaigi-Moschorhinus Subzone of the Daptocephalus AZ (upper Permian) to Lower Triassic Lystrosaurus declivis AZ (Changhsingian to Induan stages), Beaufort Group, Karoo Supergroup; known from numerous localities throughout the Eastern Cape, Free State, and KwaZulu-Natal provinces, Karoo Basin, South Africa. Huttenlocker & Botha-Brink (2013) showed that the Triassic record of the genus is typified by fewer fossils and generally smaller sizes than in the Permian.

Diagnosis—Medium-to-large eutherocephalian (basal skull length up to 260 mm) with: short, broad rostrum; narrow, slit-like pineal foramen; extremely broad, fan-shaped vomer bearing paired tubercles anteroventrally; crista choanalis broad and rounded; pterygoid teeth completely absent (shared with other akidnognathids); dentary deepened with prominent mental protuberance; upper tooth count I5:pC0–1:C1:PC3–4 (as few as two postcanines in some large specimens); spatulate upper incisors with broad, smooth facets on enamel surface (unstriated); first three upper incisors have mesiodistally elongate figure-8 cross-section; enlarged, saber-like upper canines lacking carinae or serrations (rounded in cross-section); fan-shaped ventral end of the clavicle with a scalloped posteromedial margin; small, shield-shaped interclavicle with reduced lateral rami and smooth posterior ramus; large, circular sternum lacking a posterior notch; robust femur with a dorsoventrally long, triangular internal trochanter.

Remarks—Moschorhinus specimens are locally abundant throughout the Karoo Basin, and are well represented by numerous cranial and postcranial fossils (Huttenlocker & Botha-Brink, 2013). Mendrez (1974a, 1974b) tentatively proposed synonymy with Tigrisuchus, which was based on a weathered snout collected by A. Bain and described by Owen (1876). Previous authors have referred Tigrisuchus to Gorgonopsia (e.g., Sigogneau, 1970; van den Heever, 1987). A formalized synonymy would maintain the prevailing usage of the popular name Moschorhinus, and the older name ‘Tigrisuchus,’ which has been in disuse for many decades, should be considered a nomen oblitum under ICZN Article 23.9. Other species previously attributed to the genus Moschorhinus (M. minor Broom, M. esterhuyseni Broom, and M. natalensis Brink) are also all likely junior synonyms of the type species M. kitchingi.

Vertebrae

The most complete vertebral column is preserved in NMQR 3351, which preserves 34 articulated vertebrae, comprising 27 presacral, three sacral, and four caudal vertebrae. The vertebral column is separated by two precise transverse breaks so that the atlas-axis complex and third cervical, fourth cervical–11th dorsal, 12th dorsal–fourth caudal are preserved on separate blocks (Fig. 1A). NMQR 3939 includes fragments of cervical vertebrae on the first block, likely elements of the atlas-axis complex, as well as a set of 15 articulated dorsal vertebrae on the second block (Fig. 1B). None of the centra of NMQR 3351 (apart from the atlas-axis complex and third cervical) or NMQR 3939 are exposed.

Cervical vertebrae

Atlas-axis complex—No proatlantes are preserved in NMQR 3351, but have been described in other therocephalians (Kemp, 1986; Botha-Brink & Modesto, 2011). The atlas-axis complex is well preserved and only missing the left neural arch of the atlas (Fig. 2). The neural arch is approximately L-shaped in dorsal view, but has a slight anterior projection (Figs. 2A and 2B). The dorsal lamina extends posteriorly to form the postzygapophysis, which articulates with the dorsal surface of the prezygapophysis of the axis (Figs. 2A and 2B). The anterior lamina extends laterally forming the atlantal transverse process (Figs. 2A, 2B, 2E and 2F). The atlantal transverse process is mediolaterally short and extends ventrolaterally from the neural arch (Figs. 2A, 2B, 2E and 2F). Immediately posterior to the distal end of the transverse process, separated by a break, a mediolaterally thin sheet of bone is present that extends posteriorly and is interpreted as the corresponding atlantal rib (Figs. 2I and 2J).

The atlas centrum is preserved directly below the neural arch and the majority of its structure is visible (Figs. 2A, 2B, 2G, and 2H). The dorsal surface is concave, bearing a mediolaterally broad midline trough, which forms the ventral surface of the neural canal (Figs. 2A–2D). Only the left margin of the trough is visible; it is delimited by a sharp ridge, which extends more posteriorly than laterally. The anterior surface of the atlantal centrum is complex and is composed of three articular facets similar to those described for Scaloposaurus (Kemp, 1986). The three articulatory facets all converge at the centre of the anterior surface where a circular depression is present (Figs. 2E and 2F), which differs from the condition in Scaloposaurus where a swelling is present. A dorsolaterally, and slightly anteriorly facing facet is present on either side (the right being covered by the neural arch) for the articulation with the atlantal neural arches (Figs. 2E and 2F). The left facet is relatively mediolaterally broad, with a weakly depressed lateral surface, and a convex posterior margin. Ventral to this facet the surface slopes posteromedially and a deep notch is formed at the most anterior end. The third articulatory facet, for the reception of the atlantal intercentrum, is present ventrally (Figs. 2E and 2F). The ventral margin is convex and is in direct contact with the atlantal intercentrum.

The atlantal intercentrum is a bulbous structure and is approximately kidney shaped in anterior view (Figs. 2E and 2F). The anterolateral margins are convex and the ventral margin is straight. The parapophysis is positioned on the lateral surface in the form of a raised edge to receive the capitulum of the dichocephalous atlantal rib (Figs. 2E and 2F). The tuberculum is still articulated to the distal end of the transverse process of the neural arch (Figs. 2E, 2F, 2I, and 2J). The shaft of the atlantal rib is mediolaterally narrow and dorsoventrally tall, but it is slightly deformed and it is difficult to interpret its true length.

The axis bears a dorsoventrally tall, anteriorly extended, and robust neural spine that is hatchet shaped in lateral view (Figs. 2C, 2D, 2G and 2H). In dorsal view, the anterior end of the neural spine originates as a sharp point, which expands mediolaterally increasing width posteriorly (Figs. 2A and 2B). The greatest mediolateral expansion occurs approximately two-thirds down the length of the spine, from this point the spine narrows abruptly to terminate as a sharp point. The anterior extension is best seen in lateral view where it overhangs the anterior end of the neural arch (Figs. 2C, 2D, 2G and 2H) similar to that described for Ericiolacerta (Watson, 1931), but differs from the “backwardly directed” neural spine described for Mirotenthes (Attridge, 1956: 76) and the posteriorly expanded neural spine described for Microgomphodon (Abdala et al., 2014a). The posterior margin of the neural spine is relatively straight and slightly anterodorsally inclined. The lateral surface is anteroposteriorly long and dorsoventrally concave. The concavity of the lateral lamina slopes ventrolaterally, protruding laterally at the base of the neural arch where it forms a prominent anteroposterior lateral ridge, which runs longitudinally along the base of the neural arch into the lateral margins of the pre-and postzygapophyses (Figs. 2C, 2D, 2G and 2H). A complete neural spine, which is interpreted as the neural spine of the axis, is preserved in NMQR 3939 in close association with the cervical fragments preserved posterior to the skull (Fig. 1B). The neural spine is exposed in lateral view and is similar to the axial neural spine of NMQR 3351 by being anteriorly expanded at the dorsal end and dorsoventrally concave on the lateral surface (Fig. 1B).

The axial neural arch is approximately trapezoidal in shape in dorsal view, with its anterior end being markedly mediolaterally narrower than the broader posterior end (Figs. 2A and 2B). The neural arch is fused to the centrum with no neurocentral fusion lines being visible. The prezygapophyses are mediolaterally narrow, peg-like, horizontally orientated, and are separated medially by a deeply concave sulcus (Figs. 2A and 2B). The postzygapophyses are mediolaterally broader, horizontally orientated, and separated medially by a comparatively broader and deeply concave sulcus (Figs. 2A and 2B). The postzygapophyses are considerably larger than the prezygapophyses, similar to those described for Olivierosuchus (Botha-Brink & Modesto, 2011), but differs from Ericiolacerta (Watson, 1931) in which the prezygapophyses are larger than the postzygapophyses. No anapophyses are present. The transverse processes emerge below the base of the neural arch, anteriorly, closer to the prezygapophyses (Figs. 2C, 2D, 2G and 2H). The transverse processes are robust and project ventrolaterally similar to those described for Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011).

The axial centrum is robust and amphicoelous (Figs. 2C and 2D). The lateral surface is deeply anteroposteriorly concave and the posterior margin is boarded by a prominent flat dorsoventral rim (Figs. 2C and 2D). The axial intercentrum is a large wedge-shaped bone and is fused to the anterior border of the axial centrum (no suture line is visible) (Figs. 2G–2J). The fusion of the axial intercentrum to the axial centrum forms a conspicuous anterior projection on which the atlantal centrum lies upon. The lateral surfaces of the axial centrum slope medially to meet at the midline off the ventral surface to form a flat ventral keel that runs anteroposteriorly across the centrum (Figs. 2I and 2J). The posteroventral margin of the centrum is concave, which provides accommodation for the following intercentrum (Figs. 2I and 2J).

Both of the axial ribs are preserved (Fig. 2), but they are damaged. The right axial rib is deformed and obscured by the right atlantal rib (Figs. 2I and 2J). The proximal end of the tuberculum of the left axial rib is still attached to the left transverse process of the axis (Figs. 2A and 2B). The rest of the tuberculum, capitulum, and shaft has broken off and rotated approximately 180° along the sagittal plane so that the distal end of the shaft is projecting anteriorly and the dorsal surface of the rib is facing ventrally (Figs. 2I and 2J). The axial rib is dichocephalous and mediolaterally thin. The tuberculum is dorsoventrally tall and the capitulum is comparatively low (Figs. 2I and 2J). The third intercentrum is preserved posterior to the axial centrum (Figs. 2I and 2J). It is essentially a small wedge-shaped bone and is markedly smaller than the atlantal and axial intercentra. The intercentra are similar to those described for Olivierosuchus (Botha-Brink & Modesto, 2011), Tetracynodon darti (Sigurdsen et al., 2012), and Gorynychus masyutinae (Kammerer & Masyutin, 2018a).

Postaxial cervical series—The third cervical is preserved still in articulation with the axis (Figs. 1A and 2) whereas the rest of the cervical series is preserved on the second block of NMQR 3351 (Fig. 1A). The third cervical is slightly displaced relative to the axis and the distal end of the neural spine has broken off. The fourth cervical is damaged due to the break. The fifth cervical is well preserved and the neural spine of the sixth cervical is deformed due to a crack. The seventh vertebra of NMQR 3351 is well preserved and is transitional between the cervical and dorsal series. The first vertebrae preserved on the second block of NMQR 3939 is interpreted as the seventh cervical, but it is badly damaged (Fig. 1B).

The neural spines of the fifth and sixth cervical are dorsoventrally tall, anterodorsally inclined, and markedly shorter anteroposteriorly than that of the axial neural spine (Figs. 3A and 3B). They are approximately rectangular in lateral view with straight anterior and posterior margins so that their anteroposterior length is consistent throughout the height of the spine. The neural spine of the seventh cervical is directed more dorsally and bears weakly convex and concave anterior and posterior margins respectively (Figs. 3A and 3B). The lateral ridge of the neural arch is still present on the third, fifth, and sixth cervical, but is less pronounced than the lateral ridge of the axis, and is absent on the seventh (Figs. 2C, 2D, 2G, 2H, 3A and 3B). The pre- and postzygapophyses of the third, fifth, and sixth cervical are mediolaterally broad and horizontally orientated (Figs. 2C, 2D, 2G, 2H, 3A and 3B). The prezygapophysis of the seventh cervical is similar to those of the preceding cervicals, but the postzygapophysis is orientated more vertically (Figs. 3A and 3B). The transverse processes of the third, fifth, and sixth cervical are mediolaterally short, anteroposteriorly narrow, ventrolaterally directed, and emerge more anteriorly than posteriorly from below the lateral ridge of the neural arch (Figs. 3A and 3B) similar to those described for Scaloposaurus (Kemp, 1986). In contrast, the transverse process of the seventh cervical emerges more dorsally, closer to the level of the neural arch, projects more laterally, and is more robust being anteroposteriorly broader (Figs. 3A and 3B). The lateral surface of the centrum of the third cervical is deeply anteroposteriorly concave. The lateral surfaces meet at the midline of the ventral surface to form a sharp ventral keel (Figs. 2C, 2D, 2G, 2H, 2I and 2J) similar to the cervical centra described for other therocephalians (Botha-Brink & Modesto, 2011; Sigurdsen et al., 2012; Abdala et al., 2014b, 2014a), but differing from the flat ventral keel of the axis. The anterior margin slants posteriorly approximately halfway of the height of the centrum, shortening the anteroposterior length at the ventral end. The lateral surfaces of the posterior margin bear a flat parapophysis (Figs. 2G and 2H).

Ribs

Cervical ribs

Only the proximal ends of the right cervical ribs of NMQR 3351 are exposed (Fig. 4A). The cervical ribs are dichocephalous. The tubercula of the fourth, fifth, and sixth cervical rib are dorsoventrally tall and anteroposteriorly broad (Fig. 4A). The tuberculum of the seventh cervical rib is more robust than those of the preceding ribs by being dorsoventrally taller and anteroposteriorly broader (Fig. 4A). The capitulum of the fifth cervical rib is dorsoventrally low and slender (Fig. 4A). The proximal portion of the shafts are mediolaterally thin, posteroventrally directed, and become progressively anteroposteriorly broader from the fifth cervical rib (Fig. 4A). The distal ends of shafts of the fourth, fifth, and sixth cervical ribs are not exposed, but they are likely not very long as the cervical ribs are short in all therocephalian taxa in which they are known (Fourie & Rubidge, 2007, 2009; Botha-Brink & Modesto, 2011; Sigurdsen et al., 2012). The shaft of the seventh cervical rib is long, indicated by the exposure of the distal end, which is lying under the distal end of the first dorsal rib (Fig. 1A).

Scapula

Scapulae are preserved to varying degrees in NMQR 48, NMQR 3939, BP/1/4227, and NMQR 3351. However, they are best preserved in NMQR 48, BP/1/4227, and NMQR 3351 (Figs. 5A–5L). NMQR 48 preserves the complete ventral end and a small section of the midshaft of the left scapula of which the anterior and lateral views have been exposed (Figs. 5A and 5B). BP/1/4227 preserves the complete left scapula as a separate element allowing for the description of all views (Figs. 5C–5F). NMQR 3351 preserves both the complete left and right scapulae (Figs. 5G–5L). The entirety of the lateral surface of both scapular blades is exposed. The anterior and posterior sides of the ventral ends are slightly exposed, with the right being more exposed than the left. Measurements of the scapulae are given in Table 2.

The scapula is a dorsoventrally elongated, curved bone comprised of a slender blade, a semi-circular shaft-like middle region, and a robust ventral end. In NMQR 3351, BP/1/4227, and NMQR 3939 the dorsal end is mediolaterally constricted and anteroposteriorly expanded as in other therocephalians (Huttenlocker, Sidor & Smith, 2011). The dorsal margin of the blade is only slightly anteroposteriorly convex, and the anterior and posterior margins are slightly rounded. The most dorsal end of the left scapula of NMQR 3351 possesses a conspicuous posterior expansion (Fig. 5G). This is not present on any other scapula; however, all of the other preserved scapulae are damaged along their posterodorsal margin. The lateral surface of the most dorsal end of the blade is slightly anteroposteriorly convex and the bone surface of NMQR 3351 and BP/1/4227 is extremely rough exhibiting prominent longitudinal muscle scars (Figs. 5C and 5G). The medial surface of the scapula is only visible in BP/1/4227 and it is relatively flat (Fig. 5E).

The scapular blade constricts anteroposteriorly approximately one-third from the dorsal margin becoming semi-circular in cross-section by developing a convex lateral surface and remaining flat on the medial surface. The convexity of the lateral surface continues ventrally and forms a broad dorsoventral ridge that extends to the ventral margin of the scapula. The broad ridge divides the distal half of the scapula into an anterior and posterior surface, with the former having a steeper slope than the latter. This is similar to other eutherocephalians such as Mirotenthes (Attridge, 1956), Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011), and Ictidosuchoides (Fourie, 2013), but differs from the sharp dorsoventral ridge that has been described for Microgomphodon (King, 1996). The scapula projects medially with a sharp curve approximately two-thirds from the dorsal margin (Figs. 5D, 5F, 5H and 5I). A rough fossa that is bounded by a sharp ridge on its posterior border is present on the lateral surface of NMQR 48, BP/1/4227, and NMQR 3351 for the attachment of the clavicle (Figs. 5A–5C, 5G and 5K).

The ventral end of the scapula consists of a mediolaterally thin, plate-like, triangular procoracoid buttress and a robust, transversely expanded glenoid buttress (Figs. 5A–5L). The procoracoid buttress and glenoid buttress are separated on the lateral surface by the broad ridge described above (Fig. 5C). The anterior surface of the procoracoid buttress of BP/1/4227 is smooth and weakly depressed (Figs. 5C and 5D). The posterior surface of the glenoid buttress of BP/1/4227 is weakly convex (Figs. 5C and 5F), but weakly concave and raised on the posteromedial margin in the right scapula of NMQR 3351 (Figs. 5H and 5I). No distinct protuberance on the posterior surface of the glenoid buttress is observed on any of the studied scapulae as described for ‘Zinnosaurus’ paucidens and Simorhinella (Boonstra, 1964; Abdala et al., 2014b). On the medial surface of BP/1/4227, the procoracoid buttress and glenoid buttress are separated by a deep groove (Fig. 5E) differing from that described for Simorhinella in which a ridge is present in this area (Abdala et al., 2014b). The glenoid surface of the right scapula of NMQR 3351 is approximately square in outline in ventral view and is weakly concave (Fig. 5K). In contrast, the glenoid surface is convex in BP/1/4227, but this surface has suffered damage.

An ossified cleithrum is not present in any specimen studied, but has been reported for Ericiolacerta (Watson, 1931), Pristerognathus (Broom, 1936), an undescribed akidnognathid specimen (Huttenlocker, Sidor & Smith, 2011: 415), and Ictidosuchoides (Fourie, 2013). None of the studied scapulae show any indication for the attachment of a cleithrum on the anterior margin of the blade. A facet for the attachment for a cleithrum on the anterior margin of the scapular blade has been reported for ‘Zinnosaurus’ paucidens (Boonstra, 1964). No acromion process is present in any of the scapulae as described for other therocephalian genera (Kemp, 1986; Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011).

Coracoid

Coracoids are only preserved in NMQR 48 and NMQR 3351. Both of the coracoids in NMQR 48 are preserved and they are exposed in lateral view (Figs. 6A and 6B). The majority of the posterior and ventral margins of the right coracoid are covered by matrix as are the overlying clavicle and interclavicle. The exposed surface of the right coracoid suggests it has been deformed when compared to the left coracoid which is better preserved. Only the right coracoid is preserved in NMQR 3351, but it is broken and missing the dorsal end (Fig. 6C).

The coracoid is a blade-like bone with a distinct, robust dorsal neck. In NMQR 48, the dorsal neck of the coracoids are posteriorly expanded, transversely thickened, and exhibit a rugose convex surface, which forms the ventral surface of the glenoid (Figs. 6A and 6B). The blades of the coracoids in NMQR 48 and NMQR 3351 are mediolaterally thin and flat (Figs. 6A–6C). In NMQR 48 the blades extend ventrally as well as posteriorly and attenuate to a distinct rounded tuberosity as described for Jiufengia (Liu & Abdala, 2019). The ventral margins of the blades are slightly convex, and the anterior margins are obscured, but presumably they would have been relatively straight to form the procoracoid-coracoid suture. Watson (1931), Attridge (1956), and Boonstra (1964) noted that the coracoids of Ericiolacerta, Mirotenthes, and early-diverging therocephalians were comparatively smaller than the procoracoids. The only specimen that preserves the two respective elements is NMQR 3351, although they are disassociated and slightly damaged, they appear to be of similar size (Fig. 6C). Apart from this, the coracoids of NMQR 48 and NMQR 3351 are similar to those described for other therocephalian genera (e.g., Kemp, 1986; Botha-Brink & Modesto, 2011; Liu & Abdala, 2019).

Procoracoid

Procoracoids are preserved in NMQR 48, NMQR 3939, and NMQR 3351. Only the medial surface of the most posterior portion of the right procoracoid is exposed in NMQR 48 (Fig. 6D). NMQR 3939 preserves the right procoracoid and is exposed in medial view, but it is damaged along its posterodorsal and posteroventral margins (Fig. 6E). NMQR 3351 only preserves the right procoracoid, which is still closely articulated with the right scapula (Fig. 6C).

The procoracoid is a quadrangular plate-like bone with a flat medial surface. The anterior margin is convex whereas the posterodorsal and posteroventral margins, which would have contacted the procoracoid buttress of the scapula and the coracoid respectively, are straight as described for other therocephalians (Attridge, 1956; Cys, 1967; Kemp, 1986; Botha-Brink & Modesto, 2011; Huttenlocker, Sidor & Smith, 2011; Sigurdsen et al., 2012). The posterodorsal and posteroventral margins converge to meet at the glenoid in the form of a sharp point. Although no specimen preserves an articulated scapulocoracoid, it appears that the procoracoid does not contribute to the articulatory surface of the glenoid as described for other therocephalians (Boonstra, 1964; Botha-Brink & Modesto, 2011; Sigurdsen et al., 2012) with the exception of the scylacosaurid described by Cys (1967) in which the procoracoid contributes to the anterodorsal surface of the glenoid.

A large, circular procoracoid foramen that is entirely enclosed by the procoracoid is present in all the studied procoracoids (Figs. 6C–6E), and it is positioned close to the posterolateral margin as described for early-diverging therocephalians (Boonstra, 1964; Cys, 1967; Fourie & Rubidge, 2009), as well as for the eutherocephalians Ictidosuchus (Broom, 1900), Mirotenthes (Attridge, 1956), Olivierosuchus (Botha-Brink & Modesto, 2011), Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011), Tetracynodon darti (Sigurdsen et al., 2012), Ictidosuchoides (Fourie, 2013) and Regisaurus (BP/1/5394; B. Stuart, 2022, personal observation). This differs from the more derived eutherocephalians Ericiolacerta (Watson, 1931) and Scaloposaurus (Kemp, 1986) in which the foramen is present between the procoracoid-coracoid suture as well as Bauria in which it is positioned on the scapula-procoracoid suture (Watson, 1931).

Clavicle

Clavicles are only preserved in NMQR 48 and NMQR 3351. Both clavicles are preserved in NMQR 48, but they are incomplete. The left clavicle is overlying the right scapula, but is incomplete and only represented by a small portion of the dorsal end (Figs. 5A and 5B). The right clavicle is incomplete, missing the dorsal end and the majority of the shaft. The ventral end is well preserved and is still slightly articulated with the interclavicle (Figs. 6A and 6B). Both the clavicles are preserved in NMQR 3351. The left clavicle is incomplete, missing its dorsal end. The majority of the shaft and the ventral end is preserved, but it is broken along its medial margin (Figs. 5G, 5H, 5K and 6F). The right clavicle is incomplete, missing its ventral end. The majority of the shaft and the dorsal end, which is still articulated with the right scapula, is preserved (Figs. 5I, 5J and 5L).

The clavicle is an elongated, fairly slender, curved element that is expanded at its dorsal and ventral ends which are connected by a narrow rod-like shaft. The dorsal ends of the clavicles of NMQR 48 and NMQR 3351 are flat and spatulate and are only slightly more transversely expanded than the shaft (Figs. 5B and 5J). The shafts of the clavicles of NMQR 3351 curve ventromedially and posteriorly at their ventral ends (Figs. 5H, 5I, 5K and 5L). The ventral ends of the clavicles of NMQR 48 and NMQR 3351 flare out into a dorsoventrally thin fan-like blade with a prominent posterior projection (Figs. 5K, 6A, 6B and 6F). The medial and posterior margins of the ventral end of the right clavicle in NMQR 48 are well preserved and exhibit prominent scalloped edges (Figs. 6A and 6B).

Interclavicle

Interclavicles are preserved in NMQR 48 and NMQR 3351. The ventral surface of the interclavicle of NMQR 3351 is exposed, but has suffered damage to its outer margins and the left anterior end is obscured by the ventral end of the left clavicle (Fig. 6F). The interclavicle of NMQR 48 is better preserved, but likewise the majority of the anterior end is obscured by the ventral end of the right clavicle, and the left anterolateral surface is damaged by the distal end of a rib (Figs. 6A and 6B).

The interclavicle is a small, dorsoventrally thin, flat, plate-like bone. It is anteroposteriorly short and mediolaterally broad at its anterior end in contrast to the interclavicles described for early-diverging therocephalians, which are anteroposteriorly long, mediolaterally narrow, and approximately spoon-shaped in outline (Boonstra, 1964; Fourie & Rubidge, 2009). The complete outline of the interclavicle is obscured in both NMQR 3351 and NMQR 48, but it is approximately shield-shaped, with small laterally projecting rami on either side of the anterior end and a posterior projecting ramus (Figs. 6A, 6B and 6F), similar to the interclavicle described for Scaloposaurus (Kemp, 1986) and Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011). This differs from the cruciform interclavicle described for Ericiolacerta (Watson, 1931) and Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011), which appear to have mediolaterally wide projecting lateral rami.

Although much of the anterior end of NMQR 3351 is obscured, a prominent median ridge that extends ventrally to centre of the interclavicle, is observed (Fig. 6F) similar to that described for Ericiolacerta (Watson, 1931), Scaloposaurus (Kemp, 1986) and Olivierosuchus (Botha-Brink & Modesto, 2011). The right anterolateral surface of the interclavicle of NMQR 3351 is depressed, forming a fossa for the attachment of the ventral end of the clavicle (Fig. 6F) as described for Olivierosuchus (Botha-Brink & Modesto, 2011). The posterior ramus of NMQR 3351 and NMQR 48 is mediolaterally broad and the width is consistent throughout its length (Figs. 6A, 6B and 6F). The posterior ramus of NMQR 3351 and NMQR 48 terminates as a blunt point in contrast to Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011), which terminates as a sharp point. The ventral surface of the posterior ramus of NMQR 48 is damaged, which has led to an unnatural raised lineation (Figs. 6A and 6B). The ventral surface of the posterior end of NMQR 3351 is well preserved and is smooth as described for Ericiolacerta (Watson, 1931) and Scaloposaurus (Kemp, 1986), but contrasts with Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011), which exhibits a well-developed midline ridge on the posterior ramus.

Sternum

Sterna are preserved in NMQR 48, NMQR 3351, and CGS GHG299. The sternum of NMQR 48 is preserved in its entirety and does not appear to exhibit any deformation (Figs. 6A and 6B). The sternum in NMQR 3351 is mostly complete, however it has suffered damage from breakages and as a result a fragment of the left anterolateral end is missing, although the damage does not appear to have deformed it from its natural shape (Fig. 6G). The sternum of CGS GHG299 is complete and well preserved, but a portion of the anterior end is covered with protective plaster (Fig. 6H).

The sternum is a well-ossified, large plate-like bone as described for other eutherocephalians such as Ericiolacerta (Watson, 1931), Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011), Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011), Tetracynodon darti (Sigurdsen et al., 2012), and Ictidosuchoides (Fourie, 2013). This contrasts with early-diverging therocephalians where no specimen has been reported as preserving an ossified sternum and it is presumed to have been cartilaginous (Broom, 1938; Boonstra, 1964; Fourie & Rubidge, 2009). The sterna of NMQR 48, NMQR 3351, and CGS GHG299 are circular in outline (Figs. 6A, 6B, 6G and 6H) with their length being approximately equal to their width (Table 2). Variable sternal shapes have been reported for eutherocephalian taxa such as oval for Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011) and Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011), polygonal for Tetracynodon darti (Sigurdsen et al., 2012), and diamond-shaped for Ictidosuchoides (Fourie, 2013).

The anterior end of NMQR 48 is weakly depressed for the reception of the interclavicle (Figs. 6A and 6B) and it appears that the contact between these bones is weak, similar to Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011), but contrasting to the condition in two specimens of Olivierosuchus (BP/1/3973 and BP/1/3849) in which the interclavicle and sternum are fused. The lateral sides of the ventral surface of NMQR 48, NMQR 3351, and CGS GHG299 are depressed and exhibit prominent striations that flare out towards the lateral margins of the bone (Figs. 6A, 6B, 6G and 6H) as described for Scaloposaurus (Kemp, 1986) and Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011). The posterolateral margins of NMQR 48 and CGS GHG299 are weakly crenulated similar to those described for Scaloposaurus (Kemp, 1986), but contrasts with Tetracynodon darti (Sigurdsen et al., 2012) that exhibits prominent crenulations. As in Promoschorhynchus, the posterior margin of the sternum in NMQR 48, NMQR 3351, and CGS GHG299 does not exhibit a posterior notch, unlike those present in Scaloposaurus (Kemp, 1986), Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011), and Tetracynodon darti (Sigurdsen et al., 2012).

NMQR 48, NMQR 3351, and CGS GHG299 all possess a prominent ventromedial ridge that originates at the posterior margin and extends anteriorly towards the centre of the bone, decreasing in height (Figs. 6A, 6B, 6G and 6H) as described for other therocephalians (e.g., Kemp, 1986; Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011; Huttenlocker, Sidor & Smith, 2011; Sigurdsen et al., 2012). The ventromedial ridge is less pronounced in NMQR 48 compared to that of NMQR 3351 and CGS GHG299 and only extends to approximately halfway between the posterior margin and the centre of the bone. In contrast to NMQR 48, the ventromedial ridge extends to over a third of the length of the sternum in CGS GHG299 and to the centre of the sternum in NMQR 3351 (Table 2). As with the sternal shape, the condition of the ventromedial ridge is variable among therocephalian taxa. Watson (1931: 1176) stated that the sternum of Ericiolacerta is featureless, but he did state that it was incompletely exposed. Kemp (1986) described a weak ventromedial ridge for Scaloposaurus, but did not mention its extension on the sternum. A prominent ventromedial ridge that extends from the posterior margin to the centre of the bone is present in two specimens of Olivierosuchus (Fourie & Rubidge, 2009; Botha-Brink & Modesto, 2011) similar to that of the larger NMQR 3351, but this differs from the weak ventromedial ridge described for Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011). The ventromedial ridge of Tetracynodon is distinctive as it runs along the entire length of the bone (Sigurdsen et al., 2012).

Humerus

Humeri are preserved in NMQR 48, NMQR 3939, BP/1/4227, and NMQR 3351. The left humerus is preserved in NMQR 3939, but it is broken at the midshaft. The proximal end is only exposed in ventral view and is dorsoventrally compressed, the distal end is a separate element and still articulated to the proximal ends of the ulna and radius. The humeri of NMQR 48, BP/1/4227, and NMQR 3351 are all well-preserved and afford the best description (Fig. 7). NMQR 48 only preserves the proximal portion of the left humerus, however, the complete right humerus exists in the form of a cast and photographs of the original bone (Figs. 7A, 7C, 7E and 7G). BP/1/4227 preserves a complete left humerus, which is lying underneath the skull and is only visible in ventral view (Fig. 7F). Both humeri of NMQR 3351 are complete; the right humerus is exposed so that all surfaces, apart from the ventral surface of the proximal end, are visible (Figs. 7B, 7D and 7H). The left humerus is exposed so that only the proximal, dorsal, lateral surfaces, as well as the ventral surface of the proximal end can be observed.

The humerus is a robust bone with expanded proximal and distal ends that are connected by a short diaphysis, so that in dorsal and ventral view it is hourglass-shaped (Figs. 7A, 7B, 7E and 7F). The humeri of NMQR 48 and NMQR 3351 are slightly twisted so that the acute angle between the humeral head and the long axis of the distal end is approximately 35° similar to that described for Scaloposaurus (Kemp, 1986). The humeral torsion of therocephalian humeri have been reported as 33° for Mirotenthes (Attridge, 1956), 30° for Olivierosuchus (Botha-Brink & Modesto, 2011), and between 10°–25° for the humeri of early-diverging therocephalians (Boonstra, 1964). The well-expanded proximal and distal ends of NMQR 48, BP/1/4227, and NMQR 3351 are all sub-equal in width, each measuring half the length of the bone (Table 3). This differs from the humeri described for Mirotenthes (Attridge, 1956) and Tetracynodon darti (Sigurdsen et al., 2012) in which the proximal and distal ends are not extensively wide, measuring a third of the length of the humerus and a quarter respectively. The proximal surfaces of NMQR 48 and NMQR 3351 are convex and rugose. The proximodorsal margin is strongly mediolaterally convex and conversely the proximoventral margin is strongly mediolaterally concave.

In dorsal view the proximal end of the bone is divided into three surfaces: a lateral, dorsal, and medial surface (Figs. 7A and 7B). The dorsal surface is approximately triangular in outline with the greatest mediolateral expansion at the proximal end. The triangular dorsal surface recedes mediolaterally distally to the middle of the diaphysis where a conspicuous oval fossa is present (Figs. 7A and 7B), which is particularly deep in NMQR 3351. The humeral head is dorsally inflected and is positioned on the proximodorsal margin, slightly closer to the lateral margin than the medial (Figs. 7A–7D, 7G and 7H). The humeral head is most prominent at its midpoint and recedes in height laterally and medially until the lateral and medial ends of the proximodorsal margins are raised by the greater and lesser tuberosity respectively, with the former being slightly more developed than the latter (Figs. 7A and 7B).

The lateral and dorsal surfaces are delimited by a low ridge, the anterior dorsoventral line (ADVL Sensu Boonstra, 1964). The ridge extends distally from the proximodorsal margin of the proximal end, receding in height, to approximately the centre of the diaphysis (Figs. 7A–7D). Lateral to this ridge, an anteroposteriorly long and ventrally extended lamina forms the lateral surface of the deltopectoral crest (Figs. 7C and 7D). This surface is weakly depressed at its centre and raised ventrally by a second low ridge that extends distally from the greater tuberosity (Figs. 7C and 7D). NMQR 48, BP/1/4227, and NMQR 3351 all exhibit a well-developed posteriorly and ventrally expanded deltopectoral crest (Figs. 7C–7F) in contrast to the weak deltopectoral crest described for the humeri of early-diverging therocephalians (Boonstra, 1964). The deltopectoral crest of NMQR 48 extends posteriorly to just over half the length of the bone and to just under half the length of the bone in BP/1/4227 and NMQR 3351 (Table 3). The distal end of the deltopectoral crest of NMQR 48 and NMQR 3351 sharply recedes to terminate smoothly into the shaft where it continues as a rounded rod-like flange on the ventral surface that extends distomedially to the ventral margin of the entepicondyle (Figs. 7C–7F). The ventral surface of the proximal ends of NMQR 48 and BP/1/4227 are dominated by a deeply mediolaterally concave triangular bicipital fossa (Figs. 7E and 7F). The bicipital fossa is delimited laterally by the medial surface of the deltopectoral crest and medially by a broad, rounded medioventral ridge that extends distally from the proximoventral margin (Figs. 7E and 7F).

The medial and dorsal surfaces of the proximal end are delimited by a sharp and short ridge, the lateromedial line (LML Sensu Boonstra, 1964). The ridge extends distally from the lesser tuberosity to approximately a third of the way from the middle of the shaft (Figs. 7A, 7B, 7G and 7H). The medial surface of the proximal end is smooth, dorsoventrally convex, and is delimited ventrally by the medioventral ridge described above. A large oval entepicondylar foramen is present distally on the medial surface of NMQR 48, BP/1/4227, and NMQR 3351 (Figs. 7E–7H) as in other eutherocephalians (Kemp, 1986; Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011; Huttenlocker, Sidor & Smith, 2011; Sigurdsen et al., 2012), apart from Mirotenthes of which Attridge (1956: 84) states that there is no trace of an entepicondylar foramen (although this could be due to lack of preparation in that specimen). The entepicondylar foramen is enclosed ventrally by the rod-like flange described above and opens into the ventral surface of the distal end, which bears a deep trough (Figs. 7E and 7F). There is no ectepicondylar foramen as in all other eutherocephalians (Kemp, 1986; Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011; Huttenlocker, Sidor & Smith, 2011; Sigurdsen et al., 2012) in contrast to that described for early-diverging therocephalians (Boonstra, 1964). Lateral to the trough, the surface is slightly raised and then becomes inflected, forming a sharp ridge on the lateral surface that extends from the distal margin of the ectepicondyle to almost the middle of the shaft (Figs. 7C–7F). The epicondyles of NMQR 48 and NMQR 3351 are approximately triangular in outline in dorsal view and bear a deep triangular olecranon fossa, which separates the entepicondyle and ectepicondyle (Figs. 7A and 7B). The entepicondyles of NMQR 48 and NMQR 3351 bear a conspicuous hook-like projection, which is best seen in dorsal view (Figs. 7A and 7B).

The trochlea is present on the distal surface of NMQR 48 and NMQR 3351 and separates the entepicondyle and ectepicondyle. The trochlea extends on both the dorsal and ventral surface of the epicondyle (Figs. 7A, 7B, 7E and 7F). The trochlea forms a bulbous protuberance on the distodorsal margin of the olecranon fossa, which is far more developed in NMQR 3351 than in NMQR 48 (Figs. 7A and 7B). On the distoventral margin of NMQR 48 and BP/1/4227 the trochlea forms a comparatively mediolaterally wider, but less pronounced protuberance that gradually recedes in height laterally and medially (Figs. 7A and 7B).

Radius

Radii are preserved in NMQR 48, NMQR 3939, BP/1/4227, and NMQR 3351. The distal end of the right radius is preserved in NMQR 48, but it is not well preserved and largely covered by matrix. The complete right radius is preserved in NMQR 3351, but it is lying underneath the humerus and only the proximal and distal articulatory surface, along with a small section of the anterior surface of the shaft are exposed (Figs. 8A–8C). The proximal end of the left radius of NMQR 3939 is still articulated with the proximal end of the ulna and distal end of the humerus (Figs. 8D–8G) and the distal end is preserved on the ventral side of the skull. A cast of the left forelimb elements of NMQR 3939 exists which includes portions of the mid-shafts of the ulna and the radius (Figs. 8H and 8I). The left radius is preserved in BP/1/4227 and is still articulated with the ulna, but is preserved in two pieces with a missing portion of the shaft (Figs. 8J–8M).

The radius is a short and relatively slender bone with expanded proximal and distal ends that are separated by a circular and narrow shaft. The radii of NMQR 3351, NMQR 3939, and BP/1/4227 are relatively straight, but medially inflected at their distal ends (Figs. 8A, 8I–8L). The radius of NMQR 3351 is approximately 65% of the length of the humerus differing from BP/1/4227 in which the radius is approximately 75% the length of the humerus. The proximal end of NMQR 3351 is approximately rectangular in outline and the articulatory surface is broad and shallowly concave (Fig. 8B) similar to that described for other therocephalians (Kemp, 1986; Fourie & Rubidge, 2007; 2009; Botha-Brink & Modesto, 2011; Huttenlocker, Sidor & Smith, 2011). The distal end is approximately oval in outline and the articulatory surface is flat (Fig. 8C). The proximal end is more expanded than the distal end in contrast to that described for Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011). The lateral and medial surfaces of the radius of NMQR 3351 and NMQR 3939 are delimited by a sharp longitudinal ridge on the posterior margin of the bone (Figs. 8A, 8D and 8F) as described for other therocephalians (Kemp, 1986; Fourie & Rubidge, 2007; Huttenlocker, Sidor & Smith, 2011; Liu & Abdala, 2019).

Ulna

Ulnae are preserved in NMQR 48, NMQR 3939, BP/1/4227, and NMQR 3351. The distal end of the right ulna of NMQR 48 is preserved, but as with the radius it is obscured by matrix. Only a small section of the distal end of the right ulna is exposed in NMQR 3351. The left ulna of BP/1/4227 is relatively well preserved, but is missing a section of the midshaft (Figs. 8J–8M). The proximal end of the left ulna of NMQR 3939 is preserved (Figs. 8D and 8E) and the proximal end and a portion of the midshaft are represented in the cast of the forelimb (Figs. 8H and 8I).

The proximal surface of NMQR 3939 is largely covered by matrix and by the distal end of the humerus (Figs. 8D–8G) and is damaged in BP/1/4227 (Figs. 8J–8M). From what can be observed, the proximal articulation facet is smooth and shallow (Fig. 8F). The proximal surface is slightly raised towards the olecranon region, which bears an ossified but poorly-developed olecranon process (Figs. 8D–8G) differing from the short and broad olecranon process described for early-diverging therocephalians (Boonstra, 1964; Fourie & Rubidge, 2009; Abdala et al., 2014b). The olecranon region of BP/1/4227 superficially appears to be more developed, but this is exaggerated due to the damaged proximal articulatory surface (Figs. 8J–8M). The ossified but poorly-developed olecranon process of NMQR 3939 and BP/1/4227 is generally consistent with those described for the eutherocephalians Olivierosuchus (Fourie & Rubidge, 2007; Botha-Brink & Modesto, 2011), Scaloposaurus (Huttenlocker et al., 2022), and Microgomphodon (King, 1996). The absence of an ossified olecranon process is commonly reported for small therocephalian specimens that are inferred to be skeletally immature such as those of Scaloposaurus (Kemp, 1986) and Tetracynodon darti (Sigurdsen et al., 2012), but has also been reported as being absent in the large scylacosaurid described by Cys (1967) and the large akidnognathid Jiufengia (Liu & Abdala, 2019).

The lateral surface of the proximal end of BP/1/4227 is completely obscured by the proximal end of the radius (Fig. 8J), but the posterior portion of the lateral surface of NMQR 3939 is visible (Fig. 8D). A deep fossa that extends distally is present as described for Simorhinella (Abdala et al., 2014b), but the distal extension of the fossa is uncertain due to the missing sections of NMQR 3939. The fossa does not appear to be present on the section of the shaft represented on the cast (Fig. 8H) potentially differing from the ulna of Simorhinella where the fossa is followed distally by an anterior lineation (Abdala et al., 2014b). A mediolaterally broad posterior crest is present proximally on the posterior margin of NMQR 3939 and BP/1/4227 (Figs. 8D, 8E, 8G, 8J, 8K, 8L and 8M). The posterior crest becomes reduced distally and borders the fossa on the lateral surface posteriorly as described for Scaloposaurus (Kemp, 1986) and Simorhinella (Abdala et al., 2014b). The medial surface of NMQR 3939 and BP/1/4227 are dominated by an anteroposteriorly long and shallow fossa that attenuates distally and is bordered by the posterior crest (Figs. 8F, 8G, 8L and 8M) as described for all other therocephalians in which the ulna is known (e.g., Kemp, 1986; King, 1996; Botha-Brink & Modesto, 2011; Abdala et al., 2014b).

Manus

Manual elements are preserved in NMQR 48, NMQR 3939, BP/1/4227, and NMQR 3351. NMQR 48 preserves a few carpal elements, but they are largely covered by matrix. NMQR 3939 preserves the left manus in ventral view and it is the most complete of all the studied material (Figs. 9A and 9B). BP/1/4227 preserves three metacarpals in ventral view and possible carpal elements, but they are too poorly preserved to identify (Figs. 9C and 9D). NMQR 3351 preserves the right manus in dorsal view and consists of three metacarpals (possibly four, see below), carpal, and phalangeal elements (Figs. 9E and 9F).

Ilium

Ilia are preserved in NMQR 3939, SAM-PK-K10698, and NMQR 3351. NMQR 3351 preserves both complete ilia (Figs. 10A–10C). The lateral surface of the right ilium is exposed but has suffered from slight dorsoventral compression and is damaged along its anterior margin. The proximal head of the right femur is still in articulation with its acetabular facet (Fig. 10B). The lateral surface of the left ilium as well as the acetabular facet is exposed (Fig. 10A and 10C). The left ilium of NMQR 3939 is incomplete and is only represented by the majority of the iliac acetabular contribution, which is still articulated to the rest of the acetabulum (Fig. 10D). SAM-PK-K10698 preserves a complete right ilium that is only exposed in medial view (Figs. 10E and 10F). Measurements of the ilia are given in Table 5.

The ilium is comprised of a mediolaterally thin and anteroposteriorly expanded blade with a ventrally situated iliac acetabular facet. The anterior margin of the ilium possesses two distinct processes, an anterodorsal and an anteroventral process (Figs. 10A–10C, 10E and 10F), a characteristic of all therocephalian taxa in which the ilium is known (Kemp, 1978, 1986; Fourie & Rubidge, 2007; Sidor et al., 2014). However, the two anterior processes of the iliac blade are less distinctive in early-diverging therocephalians (Boonstra, 1964; Fourie & Rubidge, 2009). The two processes are separated by a shallow triangular fossa on the lateral surface of the blade (Figs. 10A–10C) as described for Regisaurus (Kemp, 1978) and Olivierosuchus (Fourie & Rubidge, 2007). The anteroventral process of the left ilium of NMQR 3351 and SAM-PK-K10698 is short and blunt compared to the anteroventral process of the right ilium of NMQR 3351 (Figs. 10A, 10B, 10E and 10F). This is attributed to the compression and the damage to the right ilium of NMQR 3351. The short and blunt anteroventral process differs from the anteriorly extended and dorsoventrally narrow finger-like process described for Regisaurus (Kemp, 1978), Scaloposaurus (Kemp, 1986), and Olivierosuchus (Fourie & Rubidge, 2007). The anterodorsal process terminates on the dorsal margin of the blade as a broad rounded depression. Broad, low ridges extend from the distal margin of both of the anterior processes to the centre of the iliac blade where they converge dorsally just above the supraacetabular buttress. The lateral surface of the posterior half of the blade of NMQR 3351 is only slightly dorsoventrally concave with the dorsal and ventral margins of the blade attenuating in the posterior process (Figs. 10A and 10B).

The ventral base of the iliac blade is thickened through the laterally expanded supraacetabular buttress, which is present at the midline of the ilium (Figs. 10A–10D). The supraacetabular buttress extends laterally, tapering and terminating in a rounded end, which contributes to much of the dorsal surface of the iliac acetabular facet. On the anterior portion of the supraacetabular buttress, the dorsal and anterior margin of the iliac acetabular facet is deeply medially concave that sharply delimits the anterior internal surface of the iliac acetabular facet from the anteroventral edge of the ilium. Posterior to the supraacetabular buttress, the dorsal margin of the iliac acetabular facet is shallowly concave that forms a broad dorsoventrally convex surface that smoothly connects the posteroventral surface of the iliac blade to the posterior internal surface of the iliac acetabular facet. The surface of the iliac acetabular facet of NMQR 3939 and NMQR 3351 is deep and smooth and contributes to approximately half of the dorsal surface acetabulum (Figs. 10C and 10D). The surface of the iliac acetabular facet faces ventrally due to the supraacetabular buttress, but has an extensive ventrolaterally facing surface as well. A slight ridge on the posterior end of the iliac acetabular facet that runs towards the centre of the acetabulum is present in NMQR 3351 and NMQR 3939. A similar ridge has been described for an isolated ilium attributed to a therocephalian from Antarctica (Sidor et al., 2014). A shallow depression is present posterior to this ridge in NMQR 3351, but the corresponding area in NMQR 3939 is not preserved (Figs. 10C and 10D).

The medial surface of the iliac blade of SAM-PK-K10698 (Figs. 10E and 10F) is extremely similar to that of Regisaurus described by Kemp (1978). The medial surface is relatively flat, apart from the presence of a shallow triangular fossa, which is bordered by the broad ridges of the anteroventral and anterodorsal processes as on the lateral surface of the blade. The triangular depression terminates close to the base of the acetabular neck in the form of a deep crescent shaped depression, which represents the attachment point for the first sacral rib. Posterior to the ridge of the anterodorsal process at the centre of the ilium a second deep depression is present, which represents the attachment point for the second sacral rib. Posterior to this depression, on the posterior half of the iliac blade a small oval depression is present, which represents the attachment point for the third sacral rib. The medial surface of the iliac acetabular facet is slightly anteroposteriorly convex and dorsoventrally straight.

Pubis

Pubes are preserved in NMQR 48, NMQR 3939, and NMQR 3568. NMQR 48 preserves the complete right pubis in dorsal view, but a bone, possibly a sacral rib, is overlying the posterolateral margin of the blade (Fig. 11A). NMQR 3568 preserves the complete right pubis as a separate element (Figs. 11B–11E). NMQR 3939 only preserves the acetabular contribution of the left pubis (Figs. 10D, 11F and 11G). Measurements of the pubes are given in Table 5.

The pubis is comprised of a robust pubic head and a dorsoventrally thin pubic blade that are connected by a short anteroposteriorly constricted pubic neck. The pubic blade is mediolaterally and posteriorly expanded with a convex dorsal surface and concave ventral surface as described for Olivierosuchus (Fourie & Rubidge, 2007). Both the pubic blades of NMQR 48 and NMQR 3568 possess a strongly concave anterior margin, which forms a dorsoventrally thickened tuberosity on the anteromedial margin (Figs. 11A–11C and 11E). The pubic blade extends posteriorly with a smoothly convex medial margin. In NMQR 3568 the pubic blade extends laterally at the posterior end of the pubic blade attenuating to a rounded point (Figs. 11B and 11C). The medial margin of the pubic blade of NMQR 48 is largely covered by the aforementioned bone and is damaged in NMQR 3568, but it can be seen that the medial margin is deeply concave and recurves posteriorly at the pubic neck forming the anterior boarder of the obturator foramen as in other eutherocephalians, but differs from early-diverging therocephalians, which exhibit a pubic foramen that is entirely bounded in the pubis (Boonstra, 1964; Fourie & Rubidge, 2009).

Both the pubic blades of NMQR 48 and NMQR 3568 constrict to form the short pubic neck. The pubic neck expands anteroposteriorly and dorsoventrally to form the robust pubic head. The posterior surface of the pubic neck and pubic head of NMQR 48 and NMQR 3568 are shallowly depressed and are delimited from the dorsal surface by a posteroventrally sloped surface. In NMQR 3568 an obturator ridge extends from the ventral margin of the pubic head and runs along the anterior region of the ventral surface of the pubic blade terminating at the anteromedial tuberosity (Fig. 11C). The acetabular facet of NMQR 48 is not well exposed, but it can be seen that the ventral surface of the pubic head is anteroposteriorly expanded (Fig. 11A). The pubic acetabular facet of NMQR 3568 is well preserved (Figs. 11B–11D) and is oval in outline and bears a convex articulatory surface similar to that of Scaloposaurus (Kemp, 1986). In contrast, the pubic acetabular facet of NMQR 3939 is almost triangular and slightly concave, but this difference could be attributed to deformation and weathering along its ventrolateral margin (Figs. 10D, 11F and 11G).

Ischium

Ischia are preserved in NMQR 48, NMQR 3939, and NMQR 3351. NMQR 3939 preserves an almost complete left ischium that is still articulated to the acetabulum, but the ischial blade has suffered considerable damage resulting in the loss of most of the medial and posterior margins (Figs. 10D, 11F and 11G). NMQR 3351 preserves the left ischium, but only the ischial acetabular facet and a portion of the posterior surface is exposed (Fig. 11H). NMQR 48 preserves a mostly complete left ischium that is damaged along its posterior margin (Fig. 11I). Measurements of the ischia are given in Table 5.

The ischium comprises a robust ischial head followed by a short and anteroposteriorly constricted ischial neck, which expands to form the dorsoventrally thin ischial blade. The preservation of both elements in NMQR 48 (Figs. 11A and 11I) allows for the comparison of overall size where it can be seen that the ischium is considerably larger than the pubis as reported for Ericiolacerta (Watson, 1931), Scaloposaurus (Kemp, 1986), and Olivierosuchus (Fourie & Rubidge, 2007). Despite being incomplete, the iliac blade of NMQR 3939 and NMQR 48 is large, and the ventral surface is flat as described for Scaloposaurus (Kemp, 1986), but differs from the convex dorsal surface described for Olivierosuchus (Fourie & Rubidge, 2007). The anterior margin of the iliac blade of NMQR 3939 is deeply concave and forms the posterior boarder of the obturator foramen (Figs. 11F and 11G). Although no specimen preserves a complete and articulated pubis and ischium, the pubes of NMQR 48 and NMQR 3568 along with the ischium of NMQR 3939 suggest that the obturator foramen was considerably large as described for Choerosaurus (Haughton, 1929), Ericiolacerta (Watson, 1931) and Scaloposaurus (Kemp, 1986). The posterior margin of the ischium of NMQR 3351 and NMQR 3939 is strongly concave and becomes dorsoventrally thickened along the ischial neck to form the robust anteroposteriorly and dorsoventrally expanded ischial head (Figs. 10D, 11F, 11G, 11H and 11I). A prominent triangular groove is present on the posterior surface of the ischium of NMQR 3939 and NMQR 3351 and is bordered by a sharp ridge that delimits the posterior and ventral surfaces (Figs. 10D and 11F–11H). The acetabular facet of NMQR 3939 and NMQR 3351 (Figs. 10D and 11F–11H) is larger than that of the pubis and is flat as described for Scaloposaurus (Kemp, 1986), but differs from the concave ischial acetabular facet described for Olivierosuchus (Fourie & Rubidge, 2007).

Femur

Femora are preserved in NMQR 48, NMQR 3939, and NMQR 3351. NMQR 48 only preserves the proximal end of the left femur, but it is damaged. NMQR 3351 preserves both femora (Figs. 12A–12E). The right femur is complete, but it has a cross-sectional break through the proximal portion of the shaft (Figs. 12A and 12B). The proximal head is still articulated with the acetabulum, which only allows for the lateral, and partial anterior and posterior views to be observed. The left femur is incomplete and is represented by the proximal head and the proximal portion of the shaft, which are exposed in anterior, medial, and posterior views (Figs. 12C and 12D). NMQR 3939 preserves the entire left femur as three separate pieces; the proximal end, the proximal portion of the shaft, which is represented by a cast, and the distal shaft and distal end (Figs. 12F–12K).

The femur is a long, robust bone with slightly expanded proximal and distal ends that are connected by a well-defined diaphysis. The complete humerus and femur of NMQR 3351 allows for a comparison of both elements of which the femur is approximately 14% longer (Tables 3 and 6). In lateral and medial view, the femur of NMQR 3939 is only slightly sigmoidally curved, almost straight (Figs. 12H and 12I) similar to that of Olivierosuchus (Fourie & Rubidge, 2007) and other therocephalians in which the femur is known (e.g., Kemp, 1986; King, 1996), but differing from the femur of Regisaurus (Kemp, 1978), which is markedly sigmoidally curved. The shaft of the femur of NMQR 3939 is greatly twisted so that the distal condyles form an acute angle of approximately 70° relative to the proximal head, differing from those of early-diverging therocephalians, which show variable degrees of twisting between 30°–40° (Boonstra, 1964) and Regisaurus, which shows and angle of 40° (Kemp, 1978). The proximal surface of the femoral head of NMQR 3939 is convex anteroposteriorly and mediolaterally (Fig. 12F) as described for Scaloposaurus (Kemp, 1978), but differs from the flat proximal surface of the early-diverging therocephalian described by Fourie & Rubidge (2009). The outline of the proximal surface of the femoral head of NMQR 3939 is semi-circular anteriorly and becomes mediolaterally reduced, tapering posteriorly (Fig. 12F). A pronounced swelling is present on the proximomedial margin (Figs. 12F and 12I–12K) as in Choerosaurus (Haughton, 1929). The femoral head of both femora of NMQR 3351 exhibit a conspicuous anterior expansion of the proximoanterior margin (Figs. 12A and 12D), which is not observed in the femur of NMQR 3939, although the anterior surface is weathered (Fig. 12I).

The femora of NMQR 3351 and NMQR 3939 possess three trochanters that are positioned distally to the femoral head (Figs. 12A–12D, 12H and 12I–12K) as in all other therocephalians (e.g., Boonstra, 1964; Kemp, 1978, 1986; Fourie & Rubidge, 2007, 2009). The tapering posterior end of the proximal surface of the femoral head of NMQR 3351 and NMQR 3939 forms the prominent greater trochanter, which presents as a sharp ridge in NMQR 3939 and a mediolaterally broad ridge in NMQR 3351 (Figs. 12A–12C, 12H, 12J and 12K). Damage to the posterior surface of the femoral head of NMQR 3939 has led to an unnatural protruded point (Figs. 12H and 12J). The greater trochanter is mediolaterally thickened distally along the posterior margin, forming a dorsoventrally short ridge on the lateral surface of the proximal end of the femur (Figs. 12A and 12H). The lesser trochanter is present on the anterior margin of NMQR 3351 and NMQR 3939 (Figs. 12A, 12D, 12I and 12J). The lesser trochanter of NMQR 3351 and NMQR 3939 is positioned more distally from the femoral head and is in the form of a slight mediolateral swelling, but it is much less developed than the greater trochanter. As with the greater trochanter, swelling of the lesser trochanter forms a short dorsoventral ridge on the anterior margin of the lateral surface of the proximal end in NMQR 3351 and NMQR 3939 (Figs. 12A and 12J). The lateral surface of the proximal ends of NMQR 3351 and NMQR 3939 is flat and bounded by these ridges.

The femora of NMQR 3351 and NMQR 3939 possess a well-developed internal trochanter that is positioned distal to the femoral head and along the midline of the medial surface (Figs. 12B–12D and 12I–12K). The midline position of the internal trochanter is similar to that described for other therocephalians (e.g., Boonstra, 1964; Kemp, 1978, 1986), but differs from Choerosaurus where it is positioned almost on the posterior margin of the medial surface (Haughton, 1929). A low, weak ridge extends distally from the proximomedial swelling to the proximal end of the internal trochanter in NMQR 3939 (Fig. 12J). The intertrochanteric fossa is an anteroposteriorly concave, depressed surface posterior to this ridge (Fig. 12J). The internal trochanter of NMQR 3351 and NMQR 3939 is a strong, triangular flange in anterior and posterior view, that protrudes medially producing a prominent adductor ridge along the shaft (Figs. 12D and 12J). The internal trochanter gradually recedes distally along the shaft in the form of a low ridge. The medial surface anterior to the internal trochanter of NMQR 3351 and NMQR 3939 is deeply concave (Fig. 12J).

The shaft of NMQR 3351 and NMQR 3939 expands mediolaterally distally to form the well-developed lateral and medial condyles (Figs. 12B, 12E, 12G, 12I and 12K). The patellar groove of NMQR 3939 is a short and deep notch that separates the lateral and medial condyles on the dorsal surface of the distal end (Fig. 12I). The ventral surface of the distal end of NMQR 3351 and NMQR 3939 bears a mediolaterally broad and triangular popliteal fossa that separates the lateral and medial condyles (Figs. 12B and 12K). The lateral and medial condyles bear convex distal surfaces and encompass the entire distal surface of the femur (Figs. 12E and 12G). The lateral condyle of NMQR 3351 and NMQR 3939 is smaller than the medial condyle and is circular in outline in distal view (Figs. 12E and 12G). The medial condyle of NMQR 3351 and NMQR 3939 extends medioventrally and narrows distally to terminate as a sharp point so that it is approximately triangular in outline in distal view (Figs. 12E and 12G).

Tibia

Tibiae are only preserved in NMQR 3351 and NMQR 3939. NMQR 3351 preserves the complete right tibia, which is exposed in posterior view (Fig. 13A). Both tibiae are preserved in NMQR 3939 as separate elements (Figs. 13B–13E). The right tibia is incomplete, missing the distal end, and has suffered considerable anteroposterior compression at its proximal end. The right tibia is represented by two pieces: the proximal end and most of the shaft, and a small portion of the distal shaft, represented by a cast (Figs. 13B and 13C). The left tibia is complete and is represented by three pieces: The proximal end and a portion of the proximal shaft, the mid and distal shaft represented by a cast, and the distal end (Figs. 13D and 13E).

The tibia is a relatively long bone with a mediolaterally expanded proximal end and an anteroposteriorly flattened shaft. The complete left tibia of NMQR 3939 is approximately 79% the length of the femur (Table 6). The right tibia of NMQR 3351 is only slightly longer, being approximately 82% the length of the femur. The tibia of NMQR 3351 is medially bowed with a convex medial margin and concave lateral margin (Fig. 13A). The lateral margin is more straight than convex in the tibiae of NMQR 3939 (Figs. 13B–13E). The bowed tibia of NMQR 3351 differs from the straight tibia described for Ericiolacerta (Watson, 1931), an early-diverging therocephalian (Fourie & Rubidge, 2009), and Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011). The medial end of the proximal surface of NMQR 3351 and NMQR 3939 is convex and slightly anteroposteriorly constricted whereas the lateral end is anteroposteriorly expanded, fairly flat, and slopes ventrolaterally (Figs. 13A–13E). The cnemial crest of the right tibia of NMQR 3939 is distorted and is not observable in NMQR 3351. The cnemial crest of the left tibia of NMQR 3939 is present on the anterior surface of the proximal end and is positioned closer to the lateral end than the medial end (Fig. 13E). It is moderately well developed and overhangs the anterior surface of the proximal end (Fig. 13E). A deep dorsoventral groove is present approximately midway on the shaft and is positioned close to the lateral margin (Figs. 13A, 13B and 13D) similar to that described for Regisaurus (Kemp, 1978) and Olivierosuchus (Fourie & Rubidge, 2007). A sharp oblique ridge is present on the anterior surface of NMQR 3939 (Figs. 13C and 13E), similar to that described for Regisaurus (Kemp, 1978) and Promoschorhynchus (Huttenlocker, Sidor & Smith, 2011). The ridge originates weakly, close to the lateral margin of the proximal end and extends distally to the medial margin (Figs. 13C and 13E).

Fibula

NMQR 3351 is the only specimen that preserves a fibula (Fig. 13A). The fibula is a long, slender, and straight bone with slightly expanded proximal and distal ends that are connected by a constricted shaft. The fibula is a relatively featureless bone and similar to that described for other therocephalians (e.g., Attridge, 1956; Boonstra, 1964; Cys, 1967; Kemp, 1978, 1986; King, 1996; Fourie & Rubidge, 2007, 2009; Huttenlocker, Sidor & Smith, 2011).

Therocephalian postcranial anatomy

Body size and mass of NMQR 3351 and palaeobiological insights

Recent records from China have shed new light on the early diversification of the akidnognathids showing that the Laurasian taxa were primarily medium-to-large sized (BSL > 200 mm) with Jiufengia representing the largest Laurasian akidnognathid taxon at a BSL of 250 mm (Liu & Abdala, 2019). In the Karoo Basin, only Moschorhinus (and the stratigraphically lower occurring whaitsiid Theriognathus) attained a large body size similar to that of early-diverging middle Permian therocephalians (Huttenlocker & Abdala, 2015; Kammerer & Masyutin, 2018a). Crania of Moschorhinus ranges from 136 to 262 mm (Huttenlocker & Botha-Brink, 2013) with NMQR 3351 at a BSL of 240 mm being the largest individual to preserve a complete skeleton. Based on the dimensions of the skeletal material of NMQR 3351, we estimate a minimum body length of approximately 1.1 m with a maximum length likely not exceeding 1.3 m (Fig. 14). Additionally, the preservation of both the humerus and femur of NMQR 3351 allows for the estimation of the body mass of NMQR 3351 using the minimum circumference of the shafts of these elements and the general equation for quadrupedal tetrapods from Campione & Evans (2012). Using this general formula (see Supplemental Information), we estimate a body mass of approximately 84.31 kg for NMQR 3351, which is comparable in size to a large male leopard (Panthera pardus) (Stuart & Stuart, 2017).

Gorgonopsians were the primary components of the terrestrial carnivore guild in the Karoo Basin during the late Permian (Lopingian). However, the majority of the generic diversity and abundance is lost leading up to the Daptocephalus AZ (Wuchiapingian– Changhsingian) with the disappearance of the large-bodied rubidgeines Rubidgea and Aelurognathus within the older Dicynodon-Theriognathus Subzone and the smaller-bodied taxa (e.g., Cyonosaurus, Arctognathus, and Lycaenops) within the younger Lystrosaurus maccaigi-Moschorhinus Subzone (Kammerer, 2015; Viglietti, 2020; Viglietti et al., 2021; Kammerer et al., 2023; Benoit et al., 2024). Recently, Kammerer et al. (2023) showed that a step-wise and rapid turnover occurred in the apex predatory niche in the Karoo Basin with the last gorgonopsian to occupy the role being the newly described Luarasian immigrant taxon Inostrancevia africana. Although I. africana is undoubtably the largest therapsid predator to occur in the Karoo Basin during the Lystrosaurus maccaigi-Moschorhinus Subzone, it should be noted that a considerable diversity of small-to-medium sized theriodonts: gorgonopsians (e.g., Arctognathus and Cyonosaurus), the cynodont Vetusodon, and the akidnognathid therocephalian Promoschorhynchus are present along with Moschorhinus in this faunal assemblage (Abdala et al., 2019; Viglietti, 2020; Viglietti et al., 2021; Kammerer et al., 2023; Benoit et al., 2024). This is interesting to highlight because, as has been noted for the largest gorgonopsians (Kammerer, 2016), the presence of several similarly sized taxa implies that some mechanisms of niche partitioning must have occurred in this ‘mesocarnivore’ type of guild.

The postcranial anatomy of gorgonopsians, like therocephalians, is generally poorly understood, but a recent resurgence of descriptive work has provided new data points on this clade (e.g., Kammerer & Masyutin, 2018b; Sidor, 2022; Bendel et al., 2022, 2023; Sidor & Mann, 2024). This work, with the addition of the pioneering monograph on Lycaenops by Colbert (1948), provides a relatively good idea of the general bauplan of the small-bodied non-rubidgeine gorgonopsians, and thus offers a relevant point of comparison. The relative proportions of the postcranial elements of Moschorhinus shows that the appendicular skeleton, particularly the scapula, humerus, and femur are remarkably robust indicating a powerful and stocky bauplan (Fig. 14) in comparison to the gracile nature of small-bodied gorgonopsians (Colbert, 1948; Kammerer & Masyutin, 2018b; Bendel et al., 2023). Interestingly, the manual elements (metacarpals and phalanges) of Moschorhinus are surprisingly short compared to the stylopod and zeugopod (Fig. 14) in contrast to that of gorgonopsians which are generally longer and larger (Bendel et al., 2023). The general morphotypic variation of the manus, as noted by Bendel et al. (2023), coupled with the more robust appendicular anatomy of Moschorhinus may reflect a difference in lifestyle and ecology between Moschorhinus and contemporaneous gorgonopsians. Additionally, the short and robust skull, and the unstriated, enlarged, and conical canines of Moschorhinus have been interpreted as an adaptation for withstanding sustained periods of being imbedded in prey (van Valkenburg & Jenkins, 2002), contrasting with the serrated and blade-like canines of gorgonopsians, which were better suited for slashing as well as a ‘puncture and pull’ type technique (Kammerer, 2016; Whitney et al., 2020). The combination of these cranial and postcranial traits, with the addition of relatively rapid and consistent growth rates (Huttenlocker & Botha-Brink, 2013; Huttenlocker, 2014), may have provided a competitive advantage for Moschorhinus over similarly sized gorgonopsians. Furthermore, resource scarcity across the extinction acme likely disadvantaged larger predators like I. africana as opposed to the smaller-bodied Moschorhinus, which ultimately allowed for a successful, but brief occupation of the apex predator role during the PTME.