Inostrancevia africana Kammerer et al., 2023

Macungo, Zanildo, Benoit, Julien & Araújo, Ricardo, 2025, InoStranCevia afriCana, the first diagnosable gorgonopsian (Therapsida, Synapsida) from the Metangula graben (Mozambique): new anatomical observations and biostratigraphic implications, Swiss Journal of Palaeontology (12) 144 (1), pp. 1-21 : 3-16

Inostrancevia africana Kammerer et al., 2023

Referred Specimen: PPM2018-7Z .

Revised diagnose: In addition to the diagnose given by Kammerer et al. (2023), Inostrancevia africana is distinguished by the presence of rugosity and small foramina on the lateral face of the prefrontal.

General aspect of the skull: Specimen PPM2018-7Z is a large partial skull, which preserves the skull roof, occiput, and a small portion of the posterior part of the basicranium. The skull appears to have undergone dorsoventral compression and mediolateral shearing, as evidenced by the dislodging of the ventral part of the maxilla into the skull roof and the posteroventral displacement of the right zygomatic arch, respectively ( Fig. 3 ). Furthermore, the skull is traversed by a fracture through the parietalfrontal suture, and another vertical fracture separates the occiput from the dorsal half of the foramen magnum, possibly obliterating the nuchal ridge (assuming that this structure was present in this specimen). Anteriorly, the skull is crushed at the level of the prootics such that the pila antoticae are not preserved, together with the majority of the parasphenoid rostrum. The palate is not preserved. Only the large left canine is preserved.

Identification

Inostrancevia africana is diagnosed by the presence of an orbit larger than the temporal fenestra ( 11 cm vs. 9 cm, respectively); extreme narrowing of the jugal below the orbit (compared to I. alexandri ); a far posterior position of the pineal foramen; a reduced contribution of the frontal to the orbital margins; the presence of a deep parietal depression; an anteroposteriorly greatly expanded postorbital bar ventrally, the protrusion of the postfrontal onto the parietal; and the laterally facing temporal bar of the squamosal.

Locality and horizon

Specimen PPM2018-7Z was found in the Lago district, near the Mepoche Locality , nearly 3 km northwest of the town. It was collected along one of the branches leading to the Maluízo River , a site corresponding to the K 6a2 Member of the K 6 Formation of the lithological sequence in the Metangula graben ( Verniers et al., 1989). The detailed geology of the K6a2 Member is discussed in Araújo et al. (2020). This specimen was embedded in coarse-grained arkosic sandstones ( Fig. 1 ). The K6a2 Member has produced many therapsid taxa such as Daptocephalus cf. D. leoniceps and Dicynodontoides / Kingoria , enabling correlation to the fauna of the Daptocephalus AZ in the Karoo Basin of South Africa ( Araújo et al., 2020; Macungo et al., 2023).

Skull measurements

Anatomical descriptions

Dentition

Specimen PPM2018-7Z was found associated with a large, mediolaterally compressed left canine, and a badly preserved cross-section of the right canine. Only the crown of this tooth is preserved as the root is broken ( Fig. 2 ). The preserved portion of this canine is 113 mm long (apicobasally), 32 mm wide at the base and 0.3 mm wide at the tip (mesiodistally). It bears fine serrations along the mesial and distal edges, here identified as denticles (de) following the standard therapsid tooth nomenclature ( Hendrickx et al., 2015; Hoffman et al., 2023; Liu & Yang, 2022). The canine is curved distally. Its crown base is wide but it gradually tapers apically, as in other gorgonopsians ( Fordyce et al., 2012; Kermack, 1956; Liu & Yang, 2022). A shallow depression (lid) is present on the lingual surface (lifa) of the crown base in PPM2018- 7Z, but the rest of the base has a gently convex surface. Towards the apical margin, the lingual face of this canine is flat ( Fig. 2 ). The labial face of the crown is marked by many longitudinal low ridges that merge apically (apr).

The mesial and distal edges of the canine of PPM2018- 7Z have transversely thick carinae that extend apicobasally. The mesial carina (mec) is shorter than the distal one (dic), as the former does not reach either the apical nor basal ends of the crown ( Fig. 2 ). The carinae bear denticles. Although affected by large cracks, the mesial denticles are thick basally but become smaller apically in PPM2018-7Z. The density of the distal denticles increases apically and basally.

The specimen PPM2018-7Z has only two postcanines ( Fig. 3 ). These postcanines are large and elliptical (long axis oriented anteroposteriorly) in cross-section. They are clearly separated each other and from the canine. Only the root and a very small portion of the crown of the first postcanine is preserved. The second postcanine is completely preserved and does not bear serrations.

Maxilla

The maxilla is preserved as a small posterior portion of the left bone (max), which is attached to the skull, and an isolated and fragmentary right maxilla ( Figs. 3 , 4 ). Because of the dorsoventral compression of the skull, most of the lateral wall of the left maxilla is exposed in ventral view. The maxilla is tall and contacts the lacrimal and jugal posteriorly, the nasal dorsally, and the prefrontal posterodorsally. Laterally, the dorsalmost portion of the maxilla is pitted and is traversed by fractures, while the ventral portion is irregular and bears a deep depression (maxhd). This depression widens posteriorly and terminates at the contact between the maxilla and the jugal. Whether this depression is an anatomical feature (i.e., preorbital fossa) or an artefact cannot be determined because the specimen underwent significant distortion and compressions. The lateral face of the right maxilla is excavated by a shallow depression (mxld) on its anteroventral margin, immediately posterior to the canine ( Fig. 3 ). This depression is flanked by the maxillary bulges that accommodate the canine and postcanines.

Lacrimal

The lacrimal (la) is preserved on both sides and forms the anterior border of the orbit. While the right lacrimal is largely complete despite being affected by cracks, the left lacrimal preserves only the dorsalmost part of the bone. The left lacrimal is mostly visible in ventral aspect due to deformation. The lacrimal forms the lateral face of the preserved portion of the snout. It is topped by the prefrontal, and both bones share a long, anteroposteriorly extending suture in lateral view. The lacrimal has a broad posterodorsal process that forms the entire anterior wall of the orbit in ventral view ( Fig. 4C ). This process forms an interdigitating contact with the prefrontal. As does the prefrontal, the lacrimal bears irregular depressions inside the orbit. Inside the orbit, the lacrimal is perforated by a circular lacrimal foramen (laf). The suture with the jugal is unclear, but this contact seems to follow an oblique orientation.

Jugal

In Specimen PPM2018-7Z, the right jugal (ju) is anteroposteriorly elongated, dorsoventrally tall, and mediolaterally compressed ( Fig. 5 ). It extends anteriorly to form the posteroventral rim of the orbit and receives the postorbital bar along its posterodorsal surface. It is overlapped by the zygomatic process of the squamosal posteroventrally. The jugal is truncated anteriorly such that it forms only a small contribution to the suborbital bar is preserved. However, judging from the preserved portion, it is possible that the jugal would have formed the entire ventral border of the orbit. The jugal has an extensive medial contribution to the subtemporal bar as it extends far posteriorly, extending for nearly the entire anteroposterior length all of the temporal fenestra (jutp, Fig. 5B ), more than in Arctognathus curvimola where it borders only the anterior half of the temporal fenestra ( Kammerer, 2015). Only a small portion of the left jugal is preserved in contact with the lacrimal and is traversed by fractures ( Fig. 4C ). Below the postorbital bar, the jugal is dorsoventrally short in lateral and medial views ( Fig. 5A, C ). Due to this shortening of the jugal, it does not develop a distinct postorbital process in PPM2018-7Z, which is characteristic of the clade Gorgonopsia ( Rubidge & Sidor, 2001).

Fig. 4 (See legend on previous page.)

Nasal

Only a small portion of the nasal (na) is preserved anterior to the frontal in PPM2018-7Z ( Fig. 4 ). The nasal shares a sutural contact with the frontal posteriorly and overlaps the maxilla along a straight anteroposterior contact laterally. The lateral margins of the nasals are raised to form low longitudinal ridges (nar). Between these ridges, the dorsal surface of the nasal bears thin anteroposterior crests that extend posteriorly onto the frontal. Similar longitudinal crests are present on the ventral surfaces of the nasals.

Prefrontal

The prefrontal is an elongated bone that tapers anteriorly in PPM2018-7Z. Its dorsal and ventral margins are smoothly convex at the sutural contacts with the frontal and lacrimal. As in other gorgonopsians ( Boonstra, 1935; Kammerer et al., 2015, 2023; Kammerer, 2015, 2017b; Laurin, 1998; Olson, 1937), the prefrontal extends anteriorly beyond the frontal ( Fig. 4 ). Despite the taphonomic deformation, the sutures between the prefrontal, nasal, and frontal were not obliterated. Anteriorly, the right prefrontal is crushed but the left prefrontal inserts between the nasal, frontal, and maxilla, forming a convex anterior margin. Posteriorly, the prefrontal has a convex lateral margin where it borders the orbit dorsally. The orbital rim is slightly raised. A few foramina pierce the lateral surface of the right prefrontal in PPM2018-7Z. Due to poor preservation, only a small portion of the prefrontal is visible inside the orbit, and this portion forms an interdigitating contact with the lacrimal ( Fig. 4C ).

Frontal

The frontal is relatively well-preserved in PPM2018- 7Z, except for its right posteriormost margin, which is broken. It is long and expands posteriorly, resulting in a roughly trapezoidal shape ( Fig. 4A, B ). Unlike in rubidgeines, the frontal has a small contribution to the dorsal rim of the orbit in PPM2018-7Z; but this contribution appears smaller than in Arctops willistoni (Brink & Kitchingi 1953; Kammerer, 2017a). The frontal forms a roughly straight to convex suture with the prefrontal laterally and an interdigitating suture with the nasal anteriorly. The suture with the postfrontal is damaged on both sides. The mid-frontal suture is straight. The frontals bear a median depression in dorsal view ( Fig. 4A ). In contrast, the lateral edges of the frontals are raised at the contact with the prefrontal. The dorsal surface of the frontal bears low median crests that continue onto the nasal anteriorly and become more evident anteriorly ( Fig. 4A ). Internally, a short process (frvp) projects on the ventral surface of the frontal that sutures with the ascending wing of the orbitosphenoid ( Fig. 4C ).

Postfrontal

The postfrontal (pof) is a subtriangular bone that contacts the postorbital, parietal and frontals on the skull roof in PPM2018-7Z ( Fig. 4 ). It forms a straight suture with the parietal medially and an oblique one with the postorbital posteriorly in dorsal view. Despite being a small bone, it forms most of the dorsal border of the orbit. The postfrontal has a small contact with the frontal anteriorly. This contact with the frontal coincides with the large crack that traverses the skull through the orbit.

Parietal

The majority of the posterior skull roof is formed by the parietal in PPM2018-7Z, although the anterior border of this bone is difficult to determine due to the crack that traverses the orbital region ( Fig. 4 ). The parietal is transversely wide but forms a thin posterior process that inserts between the tabular and postorbital. This process tapers as it extends posteriorly. Two shallow depressions (pad) diverging obliquely from the pineal boss (pib) are present on the dorsal surface of the parietal ( Fig. 4A ). These two depressions are limited medially by thick buttresses (pab) that diverge anteriorly and surround the median parietal depression (pme). Only the posterior end of the median parietal depression is preserved and, judging from its subtriangular shape, we can predict that this depression was likely diamond-shaped as in Inostrancevia spp. ( Amalitzky, 1922; Kammerer et al., 2023). The pineal foramen is circular and is surrounded by the collar-like pineal boss in dorsal view. It is located considerably posteriorly as in Inostrancevia when compared to other gorgonopsians. Aside these depressions and buttresses, the rest of the dorsal surface of the parietal is relatively flat.

The parietal limits the postorbital and postfrontal laterally along a smoothly concave anteroposteriorly oriented suture. Its anterior end together with its contact with the frontal are damaged. Posteriorly, the parietal and postparietal contact each other occurs along a raised area in dorsal view, which is essentially an anterior continuation of the pronounced postparietal boss ( Fig. 4A , see below).

Only the left descending flange of the parietal is preserved in PPM2018-7Z in ventral view, but due to distortion, this flange is obliquely oriented rather than vertical. The descending flange (paf) is fused to the orbitosphenoid ( Fig. 4C ). The parietal flange is taller posteriorly than anteriorly ( Fig. 4C ). A smooth concavity between the descending flange and the lateral margin of the parietal forms a large depression (pavd) on the ventral surface of the parietal.

Preparietal

No evidence of a preparietal was observed in PPM2018-7Z.

Postorbital

The postorbital is T-shaped in lateral view, contributes to the skull roof, and borders the orbit posteriorly ( Figs. 4 and 5 ). It has a small contribution to the dorsal rim of the orbit, but the postorbital bar forms the entire posterior border of the orbit. Most of its horizontal component borders the temporal fenestra medially ( Fig. 5 ). Inside the temporal fenestra, the postorbital is mediolaterally thin and faces laterally. Outside the fenestra, it is expanded, flat, and faces dorsally. The postorbital forms a marked angle between the temporal fenestra and the dorsal aspect of the postorbital bar. In dorsal view, the postorbital shares an oblique suture with the postfrontal anteriorly, and contacts the parietal medially along an anteroposteriorly extending suture ( Fig. 4A ). The suture between the postorbital and parietal is slightly convex on the ventral side. This suture passes through the deep triangular depression (pavd) on the postorbital and parietal. There is a thin oblique crest (povcr) on the ventral aspect of the postorbital ( Fig. 4C, D ). The vertical component of the postorbital is anteroposteriorly broadly expanded ventrally and descends to contact the jugal. The pronounced ventral expansion of the postorbital bar in PPM2018-7Z recalls the condition in the rubidgeines Dinogorgon and Rubidgea ( Kammerer, 2016) and the inostranceviine Inostrancevia alexandri ( Kammerer et al., 2023) . A thin sheet of the jugal prevents the postorbital to contact the squamosal ventrally. The postorbital bar is sigmoidal in PPM2018-7Z as its dorsalmost part curves medially and its ventral one curves laterally, somewhat similar to specimen SAM-PK-K11457 of Arctognathus curvimola ( Kammerer, 2015) . The ventral face of the postorbital is excavated by a large shallow depression (pold) in lateral view.

Postparietal

The postparietal (pp) is subrectangular, being low dorsoventrally but mediolaterally wide, and contributes to the occiput in PPM2018-7Z ( Figs. 4A, B ; 6A, B ). Dorsally, the parietal contacts the postparietal along a roughly convex suture and the tabular laterally along a straight vertical suture. A median eminence (ppb— postparietal boss) flanked by two deep depressions (ppd) on either side is the most conspicuous features on the occipital surface. This eminence has the shape of an inverted triangle and represents the remnants of a crushed nuchal ridge. The postparietal eminence was formed by the dorsoventral compression of PPM2018-7Z. Due to the presence of fractures on the occipital surface of the supraoccipital, it is impossible to tell if the nuchal ridge originally descended on the supraoccipital. The depression on the left side of the median eminence is deeper than that on the right side due to deformation ( Fig. 6A ). The postparietal contacts the supraoccipital ventrally along a nearly horizontal suture. On its ventral margin, the postparietal is contacted by a small dorsally projecting process of the supraoccipital ( Fig. 6A ).

Tabular

The tabular (ta) is a blade-like and subtriangular bone and overlaps the postparietal, squamosal, and supraoccipital on the occiput ( Fig. 6 ). The dorsal part of the left tabular is better preserved in PPM2018-7Z although it is traversed by cracks that are filled by calcite crystals. However, the ventral portion of the tabular is completely preserved. The dorsal margin of the left tabular is smoothly convex. The full extent of the tabular is best visible on the right side, showing it is twice as tall than wide. The lateral margin of the tabular is smoothly concave but the medial margin appears straight dorsally on the left better-preserved and less deformed side and interdigitating ventrally where it sutures to the postparietal and supraoccipital, respectively ( Fig. 6A, B ). The tabular participates on the dorsal and lateral rim of the posttemporal opening where it overlaps the supraoccipital and squamosal.

Supraoccipital

The supraoccipital (su) is low and broad in PPM2018-7Z ( Fig. 6 ). Its occipital surface is generally flat; its dorsalmost margin is traversed by cracks. Despite the cracks on its surface, the suture with the postparietal remains distinguishable and extends nearly horizontally in posterior view. A low median dorsal process of the supraoccipital contacts the ventral margin of the postparietal ( Fig. 6A, B ). The foramen magnum (fm) is elliptical. A contact between the supraoccipital and exoccipitals is inferred but not visible ventrally due to co-ossification and poor preservation. Laterally, the supraoccipital is overlapped by the tabular, which excludes the supraoccipital from the margin of the posttemporal fenestra and contact with the squamosal. However, it is possible that most of this overlapping surface is the result of compression and that the supraoccipital originally formed the medial rim of the posttemporal fenestra as in other gorgonopsians ( Araújo et al., 2017). Ventrally, the supraoccipital contacts the opisthotic along an irregular subhorizontal suture.

Fig. 6 (See legend on previous page.)

Exoccipitals and basioccipital

The dorsal components of the exoccipitals are poorly preserved and the ventral components are undistinguishably fused to the basioccipital on the occipital condyle (oc) ( Figs. 6 , 7 ). The condylar portion of the basioccipital (bo) is robust as in other gorgonopsians ( Sigogneau-Russell, 1989), and its ventral border is smoothly rounded. The ventral surface of the basioccipital shows well-developed basioccipital tubera (bot) that project anteriorly. Deep excavations (boex) flank the occipital condyle either side and join each other anteriorly, forming a depression on the ventral surface of the basioccipital and the parabasisphenoid ( Fig. 7 ). This excavation has the shape of an inverted Y in ventral view. Ventrally, the basioccipital tubera are very short but thick and prominent anteriorly where they bound the posterior rim of the fenestra ovalis (fo). The fenestra ovalis is circular and its anterior and dorsal margins are formed by the parabasisphenoid and prootic, respectively. The basioccipital-parabasisphenoid suture is convex anteriorly ( Fig. 7 ). The basioccipital tubera contact the opisthotics laterally and the two bones bound the circular jugular foramen (jf). The basioccipital forms the medial margin of the foramen whereas the opisthotic and exoccipital bound its anterior and dorsal rims. It is difficult to estimate the contribution of the exoccipital to the jugular foramen because this bone is fused to the basioccipital.

Opisthotic

Only the right opisthotic (op) is completely preserved in PPM2018-7Z ( Figs. 6 , 8 ). It consists of a robust, laterallyextending buttress from the remnants of the exoccipital and contacts the squamosal. The opisthotic is marked by three surfaces on its buttressed region, almost making it pyramidal in shape. One facet is oriented dorsally, another is facing ventrally (they are separated by a posteriorly projecting blunt crest) and another facet faces anteriorly. These surfaces are flat and separated by long horizontal crests. The opisthotic has a small contribution to the ventral border of the posttemporal fenestra in PPM2018-7Z; it is largely overlapped by the squamosal inside the fenestra ( Fig. 6 ). This overlap extends laterally and anteriorly, covering half of the anterior face of the opisthotic. The posttemporal fenestra is small and circular in PPM2018-7Z. In posterior view, the lateral margin of the opisthotic is characterised by a low eminence dorsally (ope) and a robust condyle ventrally (opc) ( Fig. 6C ). This dorsal eminence served essentially for attachment with the squamosal. Similar eminences bordering the lateral margin of the opisthotic are present in the Permian gorgonopsian specimen GPIT-PV-60854 ( Araújo et al., 2017). A well-developed ventral condyle of the opisthotic similar to that of PPM2018-7Z is unknown in other gorgonopsians ( Araújo et al., 2017; Kammerer & Masyutin, 2018; Kammerer & Rubidge, 2022; Kammerer et al., 2023; Sigogneau, 1970). However, a low swelling of the opisthotic is present on the ventrolateral portion of the opisthotic in Arctognathus curvimola ( Kammerer, 2015) . Based on its position and morphology, this ventral condyle (and the ventral swelling) in gorgonopsians is homologous to the tympanic process of dicynodont synapsids (Cox 1959).

Squamosal

The right squamosal preserves its zygomatic ramus (sqz) and dorsal ramus (sqd) in PPM2018-7Z; the left squamosal is broken off ( Fig. 6A ). The dorsal process is wedged between the tabular and postorbital, forming most of the posteromedial wall of the temporal fenestra. Anteriorly, the dorsal process of the squamosal overlaps the supraoccipital and opisthotic inside the temporal fenestra ( Fig. 6B ). There, it forms the anterodorsal wall of the posttemporal fenestra. An embayment (sqs) is formed between the dorsal and zygomatic processes of the squamosal. Posteriorly, the dorsal process is short in PPM2018-7Z but longs posteriorly in rubidgeines ( Kammerer, 2016).

In posterior view, the squamosal dorsally overlaps the opisthotic along its entire length. However, it is excluded from the border of the posttemporal fenestra in posterior view as it is topped by the tabular inside the fenestra ( Fig. 6A, B ). The medial border of the squamosal that overlaps the opisthotic in posterior view forms a vertical crest (sqvc) that becomes thicker ventrally. From this vertical crest, the squamosal expands laterally to form the zygomatic process. The zygomatic process is dorsoventrally tall, transversely narrow, and curved medially in PPM2018-7Z ( Fig. 5A, B ). Its lateral surface does not bear the squamosal ridge present in Nochnitsa ( Kammerer & Masyutin, 2018) . The process contacts the jugal medially and extends anteriorly to the postorbital region but not beyond the postorbital bar. The zygomatic process of the squamosal and the postorbital bar are separated by the jugal ( Fig. 5B ). Posteriorly, the zygomatic process bears an oblique buttress (sqpb) bearing a shallow squamosal sulcus (sqs) on its dorsal and ventral sides ( Fig. 6A, B ). As in Phorcys dubei and other gorgonopsians ( Kammerer & Rubidge, 2022), the squamosal sulcus continues onto the subtemporal bar in PPM2018-7Z. The articular surface for the quadrate is not preserved in PPM2018-7Z.

Prootic

In PPM2018-7Z, the prootic is a dorsoventrally low but mediolaterally wide due to the dorsoventral compression of the anterior wall of the occipital plate. It is well-preserved except for the pila antotica which is broken off ( Fig. 8B ). Despite the loss of the pila antotica, a notch is visible behind its hypothesised position, forming the trigeminal notch. The prootic overlaps the basisphenoid (corresponding portion designated as the parasphenoid-basipresphenoid complex in Araújo et al., 2017). It contacts the opisthotic laterally and the supraoccipital posteriorly. As is typical for gorgonopsians ( Araújo et al., 2017), the prootics meet along the midline of the skull, bordering the foramen magnum anteriorly and the dorsal half of the posterior wall of the sella turcica.

The prootic in PPM2018-7Z can be divided into two units, a main body laterally and a medial component. The lateral surface of the main body is formed by a subvertical, thick buttress (prb) that contacts the supraoccipital posteriorly and descends to meet the opisthotic ( Fig. 8B, C ). The nature of this contact is difficult to determine due co-ossification and to poor preservation. The subvertical buttress of the prootic slopes anteriorly to form an interdigitating contact with the parabasisphenoid. Near the region where the pila antotica used to be, the prootic is much lower compared to its posterior portion and bears a shallow depression (prd) ( Fig. 8B, C ). There is no visible facial foramen in specimen PPM2018-7Z. Ventrally, the prootic participates in the anterior margin of the fenestra ovalis in PPM2018-7Z.

The medial component of the prootic is low and located between the two bases of the pilae antoticae. It sits on the posterior portion of the parabasisphenoid, and both contribute to the posterior border of the sella turcica (stu). There is a vertical ridge (prvr) on the anterior face of the medial component of the prootic, exactly at the meeting point of the prootics ( Fig. 8C ). This ridge thickens ventrally as it descends to the parasphenoid in PPM2018-7Z ( Fig. 8C ).

Parabasisphenoid

Only the posterior half of the parasphenoid + basipresphenoid is preserved in PPM2018-7Z ( Fig. 8A ). The parasphenoid + basipresphenoid and basipostsphenoid cannot be discerned individually. As described in the section on the prootic, the parabasisphenoid (pbs) sutures to the prootic and descends to bound the fenestra ovalis anteromedially. The preserved portion of the parabasisphenoid is rectangular in lateral view ( Fig. 8D ) even though its posterior margin is smoothly concave at its contact with the prootic. Its lateral surface is marked by a horizontal eminence (pshe) that borders horizontal depressions (pshd) on its ventral and dorsal side. The ventral depression is shallower and longer than the dorsal one. The dorsal depression is likely the entrance to the Vidian canal as reconstructed for other gorgonopsians ( Araújo et al., 2017).

In dorsal view, the parasphenoid + basipresphenoid send two diverging cylindrical clinoid processes (clp) posteriorly to the prootic. These clinoid processes are clearly distinguishable and lend the parasphenoid a subtriangular aspect in dorsal view, with the base positioned posteriorly, marking a sutural contact with the prootic ( Fig. 8B, C ). A deep triangular depression is present between the clinoid processes and the dorsum sellae of the prootic, designated as the sella turcica (stu), which tapers anteriorly as in other gorgonopsians ( Araújo et al., 2017). The vertical crest of the prootic traverses the anterior face of the dorsum sellae ( Fig. 8B, C ). The parasphenoid + basipresphenoid has a weak eminence dorsally, immediately anterior to the depression for the sella turcica. In addition, the dorsal surface of the parasphenoid is excavated by a large circular foramen for the cerebral carotid arteries (ca). This foramen is bounded anteriorly by the tuberculum sellae (ts).

The inverted V-shaped basisphenoidal tubera (pbst) extend posteriorly to form the anterior borders of the fenestrae ovales. Both tubers form buttresses that widen posteriorly in ventral view ( Fig. 8A ). There is a deep excavation (boex) extending from the basioccipital to the parabasisphenoid, bordered laterally by the basisphenoid tubera.

Pterygoid

Only an isolated left transverse process of the pterygoid is preserved in PPM2018-7Z. This process expands and curves posteriorly as it extends laterally ( Fig. 9 ). In ventral view, the median surface of the transverse process is excavated by a shallow depression. The transverse process does not bear teeth in PPM2018-7Z. Medially, there are three anteroposterior crests formed at the intersection of the transverse process and the main body of the pterygoid (note that much of the main body is broken in this specimen). A thin, rectangular sheet of the ectopterygoid (ect) covers the anterior surface of the transverse process. In anterior view, the lateral margin of the transverse process is tall, oblique with a rugose lateral face ( Fig. 9B ). A deep elliptical depression (tpt at) is present on the anterior surface of the transverse process of the pterygoid in PPM2018-7Z. Posteriorly, the process is marked by a large triangular fossa (tpt pf) that is limited by the crestlike margins of the process.

Orbitosphenoid

The orbitosphenoid is very fragmentary in PPM2018- 7Z ( Fig. 4C ). It can be inferred that the orbitosphenoid wings collapsed against the ventral surface of the parietal and frontal during postmortem crushing of the skull. The orbitosphenoid wings extended along the anteroposterior axis of the skull, and each wall of the wings is mediolaterally compressed. The median septum is not preserved, but the orbitosphenoids must have been Y-shaped in PPM2018-7Z as in other gorgonopsians. The dorsal wings are in sutural contact with the short descending processes of the parietals and possibly the frontals more anteriorly. The suture with the frontal is obscured by matrix and cracks.

Phylogenetic results

Our phylogenetic analysis recovered PPM2018-7Z as a member of the “Russian gorgonopsian clade” and sister taxon to Inostrancevia africana ( Fig. 10 ). The sister position of PPM2018-7Z to Inostrancevia africana is supported by two synapomorphies. The jugal is extremely low below the postorbital bar (char. 30) in Inostrancevia africana and PPM2018-7Z (character-state 1) ( Fig. 5 ; Kammerer et al., 2023), while it is comparatively tall in Inostrancevia alexandri (character-state 0). A tall jugal is also convergently present in most rubidgeines ( Broili & Schröder, 1934; Colbert, 1948; Kammerer, 2015, 2016, 2017a, 2017b; Laurin, 1998). Specimen PPM2018-7Z also shares the anterior extension of the zygomatic process of the squamosal reaching the postorbital bar (char. 33) with Inostrancevia africana (character-state 1). Conversely, the zygomatic process of the squamosal terminates ventral to the temporal fenestra in Inostrancevia alexandri (character-state 0). This character is also convergently present in some rubidgeines (e.g., Leontosaurus and Dinogorgon ).

In our analysis, PPM2018-7Z is a member of the subfamily Inostranceviinae based on three characters, char. 27, 42 and 43. Inostranceviines are the only Russian clade members characterised by the absence of a preparietal bone (char. 27). The absence of the preparietal occurs convergently in the African clade gorgonopsians including some rubidgeines ( Kammerer, 2015, 2016). In addition, the posterior process of the parietal is confined to the skull roof in Inostranceviinae (char. 42), whereas it extends between the tabular and squamosal in other gorgonopsians. Lastly, Inostranceviinae is diagnosed by a tall occipital plate (occipital height greater or equal to 50% of width) (char. 43), which unlike the broad plate (<40% of width) in the other Russian clade gorgonopsians. However, this condition is also present in all basal African clade gorgonopsians, and the basal rubidgeines Smilesaurus and Aelurognathus .

PPM2018-7Z is excluded from Rubidgeinae because it lacks their pachyostosis and prominent supraorbital bosses ( Kammerer, 2016). In addition, Rubidgeinae has a transversely expanded subtemporal bar ( Kammerer, 2016), whereas the bar is transversely narrow in PPM2018-7Z and in all other known gorgonopsians ( Sigogneau, 1970). The squamosal has a broader contribution to the occiput than the tabular (char. 39) in all African clade gorgonopsians, but this character is absent in PPM2018-7Z and the Russian gorgonopsians. PPM2018-7Z thus cannot be referred to the African clade gorgonopsians.

Figures

Fig. 3 The right maxilla of PPM2018-7Z in A lateral,B medial and C ventral views. Ca canine, mxld lateral depression of the maxilla, pc1 and pc2— first and second postcanines

Fig. 1 Geology and geographical location of PPM2018-7Z. Adapted from Araújo et al. (2020)

Fig. 2 Canine of PPM2018-7Z in A-distal, B-mesial, C-lingual, D-Labial. E-closer view of the basal-lingual surface,F-closer view of the apico-lingual surface. apr apicobasal ridges, de denticles, dic distal carina, lafa labial surface, lid lingual depression, lifa lingual surface, mec mesial carina. Panels E and F are not in scale

(See figure on next page.) Fig. 4 Skull of PPM2018-7Z in A-dorsal and C-ventral views; B and D are the respective interpretative drawings. Bo basioccipital, fr frontal, frvp frontal ventral process,ju jugal, la lacrimal, laf lacrimal foramen,max maxilla,maxhd maxilla horizontal depression,na nasal, nar nasal dorsal ridge, ob orbitosphenoid, or orbital opening, pa-parietal, pab-parietal buttress, pad-parietal depression,paf parietal descending flange, pavd parietal ventral depression, pi pineal foramen, pib pineal boss,pme parietal medial excavation, po postorbital, pof postfrontal, povcr postorbital ventral crest,pp postparietal, ppb postparietal boss,prf prefrontal,ta tabular,sq squamosal, su supraoccipital

Fig. 5 Specimen PPM2018-7Z in A-right lateral, B-closer view of the zygomatic arch, C-medial view of the zygomatic arch. Fr frontal, ju jugal, jutp jugal temporal process,la lacrimal,na nasal,op opisthotic, opc opisthotic condyle,pa parietal, po-postorbital, pold-postorbital bar depression, pof-postfrontal, pr prootic, prf prefrontal, sq squamosal, sqs squamosal sulcus, sqz zygomatic process of the squamosal, su-supraoccipital.C not in scale

Fig. 4 (See legend on previous page.)

(See figure on next page.) Fig. 6 Occiput of PPM2018-7Z in A-posterior view, C-ventral view of the opisthotic,and B-interpretative drawing of the occiput. bo basioccipital, eo exoccipital, fm foramen magnum, jf jugular foramen, oc occipital condyle, op opisthotic, opc opisthotic ventral condyle,ope opisthotic posterior excavation, pa parietal, po postorbital,pp postparietal, ppb postparietal boss, ppd postparietal depression, ptf posttemporal fenestra, sq squamosal, sqd squamosal dorsal ramus, sqpb squamosal posterior buttress, sqs squamosal sulcus,sqvc squamosal posterior vertical crest, sqz squamosal zygomatic process, su supraoccipital, ta-tabular. C not in scale

Fig. 7 The braincase of PPM2018-7Z in ventral.boex-basioccipital ventral excavations, bot basioccipital tubera, fo fenestra ovalis, jf jugular foramen, oc occipital condyle, op opisthotic, pbs parabasisphenoid,pbst parabasisphenoidal tubera, sq squamosal,su supraoccipital,ta tabular

Fig. 8 Braincase of PPM2018-7Z in A-anterodorsal, B-dorsal, and C-lateral views. Ca carotid foramina,clp clinoid process, fm foramen magnum, op opisthotic, pa parietal, pbs parabasisphenoid, po postorbital, pr prootic, prb prootic subvertical buttress, prvr prootic vertical ridge, prd prootic depression, pshe parasphenoid horizontal eminence, pshd parasphenoid horizontal depression, psr parasphenoid rostrum, ptf posttemporal fenestra,sq squamosal, stu sella turcica, su supraoccipital, tn trigeminal notch, ts tuberculum sellae. C and D are not in scale

Fig. 9 The transverse process of the pterygoid of PPM2018-7Z in A ventral, B dorsal, C anterior,D posterior views. Ect ectopterygoid, tpt at anterior trough of the transverse process, tpt pf posterior fossa of the transverse process, tpt vc ventral crests of the transverse process, tpt vd ventral depression of the transverse process

Fig. 10 Phylogenetic relationships of PPM2018-7Z. Bremer Support and Symmetric Resampling values are indicated above and below nodes, respectively. Synapomorphies are indicated in Figure S1 in the Supplementary files

Skull measurements