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KAWINGASAURUS FOSSILIS COX, 1972 Specimen: GPIT-PV-117032 (formerly GPIT/RE/9272). Orbitosphenoid: The orbitosphenoid (Fig. 9) is a complex composed of two dorsally directed wings posteriorly and the vertical median process anteriorly often called the mesethmoid in cistecephalids (Keyser, 1973; Laass & Kaestner, 2017; Angielczyk et al., 2019). It contacts the frontal dorsally and the parasphenoid ventrally. The orbitosphenoid is nearly rectangular in lateral view and hosts the olfactory bulbs on its dorsal portion. The wings (obw) in GPIT-PV-117032 have the usual Y-shaped cross-section. The lateral wings are oriented almost vertically in anterior view and connect to the body of the bone at a right angle (Fig. 9A). The dorsal vertical portion of the wings is thin, whereas the horizontal portion is thicker. In anterior view, the base of the wing is excavated by a shallow sulcus (obasu, Fig. 9A) that descends ventromedially for a short distance. The anteriormost half of the orbitosphenoid comprises the median vertical process (obvp), which forms a horizontal dorsal plate (obpl) dorsally and descends to form a thick vertical plate ventrally that articulates with the parasphenoid rostrum (Fig. 9A). The dorsal horizontal plate articulates with the frontal dorsally. The median process separates the olfactory cavities (ofc, Fig. 9A), which are relatively expanded in Kaaeingasaurus compared to Myosaurus and Pristerodon (height-to-width ratio 2.0 in Kaaeingasaurus vs. 1.7 in Myosaurus vs. 1.8 in Pristerodon). In dorsal view, the horizontal plate of the vertical process is triangular and is excavated by a long anteroposterior sulcus (dsu, Fig. 9B). In lateral view, the orbitosphenoid in Kaaeingasaurus is relatively longer anteroposteriorly than in Myosaurus (Fig. 9C). The wings are well separated from the mesethmoid and their lateral surfaces are slightly convex. Their dorsal margins are horizontal and flat to articulate with the frontal, as in Pristerodon. The ventral margin of the wing expands posteriorly and horizontally, giving it a C-shaped posterior margin. The anterior margin of the wings appears S-shaped in lateral view. In dorsal view, the gutter (obgu) formed by the two wings is anteroposteriorly short and inclined posteriorly. There is a notch between the median vertical process and the orbitosphenoid wings in lateral view (obno). In lateral view, the vertical plate of the median vertical process has a horizontally oval outline topped by the rectangular shape of the dorsal plate dorsally. Pterygoid: The pterygoid (pt, Fig. 9 D-F) displays the typical X-shape dicynodont morphology in ventral view. In GPIT-PV-117032, the pterygoid is almost completely preserved except for the right quadrate ramus. The quadrate ramus in Kaaeingasaurus diverges from the median sagittal plane at an angle of about 80°. The anterior palatal ramus of the pterygoid has a concave lateral surface observed in dorsal view, and it forms an angle of 30° with the median sagittal axis of the skull. The angle between the palatal and quadrate rami of the pterygoid is 83°. As observed in lateral view, the palatal ramus is taller than the quadrate ramus (Fig. 9E). The posterior end of the quadrate ramus deepens ventromedially in lateral view. Medially, the posteriormost region of the quadrate ramus has a convex surface that articulates with the quadrate. The palatal ramus of the pterygoid is thicker ventrally than the quadrate ramus and terminates anteriorly in an irregular suture with the ectopterygoid (Fig. 9F). In ventral view, the two pterygoids meet at the midline of the median horizontal plate in Kaaeingasaurus, as in most cistecephalids. The ventral exposure of the pterygoid median plate in Kaaeingasaurus is short compared to the parabasisphenoid at the median sagittal axis (Fig. 9F), as noted in Angielczyk et al. (2019). Kaaeingasaurus lacks the crista oesophagea, with the median pterygoid plate being flat (Fig. 9F), and also lacks an interpterygoid vacuity, as noted by Cox (1972). An interpterygoid vacuity is also essentially absent in Cistecephalus (Keyser, 1973; Angielczyk et al., 2019), contrasting with the condition in cistecephalids like Kembaaeacela and Cistecephaloides (Cluver, 1974a; Kammerer et al., 2016; Angielczyk et al., 2019), which have small openings for this structure. The quadrate ramus is broad posteriorly but mediolaterally compressed towards the median plate in ventral view., Published as part of Macungo, Zanildo, Benoit, Julien, Fernandez, Vincent & Araújo, Ricardo M N, 2023, X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny, pp. 1-46 in Zoological Journal of the Linnean Society 198 (1) on page 25, DOI: 10.1093/zoolinnean/zlac033, http://zenodo.org/record/7922143, {"references":["Cox CB. 1972. A new digging dicynodont from the Upper Permian of Tanzania. In: Josey KA, Kemp TS, eds. Studies in Vertebrate eVolution. Edinburgh: Oliver and Boyd, 73 - 189.","Keyser AW. 1973. A preliminary study of the type area of the Cistecephalus Zone of the Beaufort Series, and a revision of the anomodont family Cistecephalidae. Geological SurVey of South Africa 62: 1 - 71.","Laass M, Kaestner A. 2017. Evidence for convergent evolution of a neocortex-like structure in a Late Permian therapsid. Journal of Morphology 278: 1033 - 1057.","Angielczyk KD, Benoit J, Rubidge BS. 2019. A new tusked cistecephalid dicynodont (Therapsida, Anomodontia) from the Upper Permian Upper Madumabisa Mudstone Formation, Luangwa Basin, Zambia. Papers in Palaeontology 7: 405 - 446.","Cluver MA. 1974 a. The skull and mandible of a new cistecephalid dicyndont. Annals of the South African Museum 64: 137 - 155.","Kammerer CF, Bandyopadhyay S, Ray S. 2016. A new taxon of cistecephalid dicynodont from the Upper Permian Kundaram Formation of India. Papers in Palaeontology 2: 569 - 584."]}

Eumantelliidae (outgroup) BP/1/2642: Pristerodon mackayi Huxley, 1868, Balfour Formation, Cistecephalus Assemblage Zone, Karoo Basin, Wuchiapingian (Late Permian). Tomography performed at the ESI. Isotropic voxel size: 0.0469 mm METHODS, Published as part of Macungo, Zanildo, Benoit, Julien, Fernandez, Vincent & Araújo, Ricardo M N, 2023, X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny, pp. 1-46 in Zoological Journal of the Linnean Society 198 (1) on page 3, DOI: 10.1093/zoolinnean/zlac033, http://zenodo.org/record/7922143, {"references":["Huxley TH. 1868. On Saurosternon bainii and Pristerodon mckayi, two new fossil lacertilian reptiles from South Africa. Geological Magazine 5: 201 - 205."]}

MYOSAURUS GRACILIS HAUGHTON, 1917 Specimens: BP/1 /2690, BP/1 /2701a (the description is a composite of the two specimens). Orbitosphenoid: The orbitosphenoid of Myosaurus displays the typical Y-shape in anterior view (Figs 2, 6). It is generally thicker than in Pristerodon, shorter dorsoventrally but mediolaterally wider (height-to-width ratio 0.8 in Myosaurus vs. 1.6 in Pristerodon). These different proportions may be a by-product of the allometric effect determining the lower limit of the olfactory bulbs, which then may be proportionally larger in Myosaurus. As in other dicynodonts, the orbitosphenoid comprises a vertical median process (obvp, the mesethmoid) anteriorly and the dorsally projecting wings (obw) posteriorly (Castanhinha et al., 2013). The gutter (obgu) that hosts the olfactory bulbs dorsally is wider than in Pristerodon. In anterior view, the orbitosphenoid has tall wings that open at a greater angle from the sagittal plane, which results in a broad olfactory cavity. The wings are less curved than in Pristerodon (Fig. 6A). The median vertical process (obvp) has a prominent vertical crest (obacr) on its anteriormost edge that is flanked by two lateral sulci (obasu) visible in anterior view. The dorsal aspect of the median process of the orbitosphenoid thickens dorsally in Myosaurus and bears a distinct horizontal fossa (obdfo, Fig. 6B). Anterior to this fossa, an approximately 1.4 mm long spine (obsp) projects anteriorly in the prolongation of the medial wall. In lateral view, the orbitosphenoid is subrectangular in Myosaurus. It is short anteroposteriorly compared to Kaaeingasaurus (length-to-width ratio 0.9 in Myosaurus vs. 1.9 in Kaaeingasaurus). The dorsal margin of the wings is not horizontal as in Pristerodon, but slightly curved (Fig. 6C). The plate-like vertical wall, which supports the wings of the orbitosphenoid, is dorsoventrally short in Myosaurus and it is traversed by two oblique crests (ltcr) in lateral view (Fig. 6C). The ventralmost crest is long, and the dorsal one is much shorter. Pterygoid: The pterygoid (pt) is incomplete in both studied specimens of Myosaurus, missing the left quadrate ramus in specimen BP/1/2701a, and the left palatal ramus and both quadrate rami in specimen BP/1/2690 (Figs 2H, 6). It has the typical X-shaped dicynodont morphology in ventral view. The palatal rami (aptr) are more horizontal than in Pristerodon, forming an angle of 22° with the anteroposterior median axis of the skull. The quadrate ramus (ptqr) angles ~61° from the sagittal axis of the skull and ~102° from the palatal ramus. The palatal ramus of the pterygoid in Myosaurus is longer than the quadrate ramus (Fig. 6G). In dorsal view, the palatal ramus of BP/1/2701a is mediolaterally thinner in Myosaurus than in Pristerodon. On the anterior half of the palatal ramus, the pterygoid of Myosaurus is excavated by a narrow anteroposterior groove (pt gr) dorsally (Fig. 6D, G). Posterior to this groove, there is an anteromedial process (pt amp) projecting over the palatal ramus and terminating posteriorly at the anterior end of the pterygoid median plate in specimen BP/1/2701a (Fig. 6G). This process is damaged in specimen BP/1/2690. The quadrate ramus is co-ossified to a small portion of the epipterygoid dorsally. In lateral view, the palatal ramus in Myosaurus is taller than the quadrate ramus. The specimens of Myosaurus described here do not have a ventral keel (Fig. 6E, H), which is consistent with previous work on Myosaurus in which this structure is not described (Haughton, 1917; Hammer & Cosgriff, 1981), but Cluver (1974b) reports the presence of this structure on the anterior palatal ramus of the pterygoid. The anteromedial process is triangular and gives a Y-shape to the pterygoid in lateral view in specimen BP/1/2701a (Fig. 6H). This process is longer and more developed dorsally than in Pristerodon. It forms an angle of 52° from the rest of the palatal ramus in Myosaurus specimen BP/1/2701a. The quadrate ramus of the pterygoid attaches to the median pterygoid plate on the short posterior process of the median pterygoid plate. The quadrate ramus has a dorsoventrally flattened and pointed end in lateral view in BP/1/2701a (Fig. 6H). In ventral view, the palatal ramus of the pterygoid has a constant width (Fig. 6F). The median plate of the pterygoid (ptmp) is narrow in Myosaurus. In ventral view, it contacts the basisphenoid along an interdigitating suture posteriorly and sends a short process posteriorly to meet the clinoid process of the basisphenoid (Fig. 6F). Myosaurus has a V-shaped crista oesophagea (co) that converges posteriorly on the midline between the two carotid foramina and bifurcates anteriorly onto the palatal rami. In BP/1/2690, the crista oesophagea is flat, but in the better-preserved specimen SAM-PK-K10974, it forms a thin median ridge. This difference between the two specimens may be the result of taphonomy or preparation. The suture between the two pterygoids is visible and marked by a weakly pronounced anteroposterior furrow (apf) at the midline (Fig. 6F). The interpterygoid vacuity is narrower and more elongated in Myosaurus than in Pristerodon. In ventral view, the quadrate ramus is expanded anteriorly and has a robust posterior edge. Epipterygoid: The epipterygoid is a vertically elongated braincase sidewall element that usually rests on the quadrate ramus ventrally and ascends to contact the descending flanges of the parietal dorsally in dicynodonts (Keyser, 1973, 1974; Angielczyk & Sullivan, 2008; Castanhinha et al., 2013; Angielczyk & Kammerer, 2017; Laass & Kaestner, 2017; Angielczyk et al., 2019). The epipterygoid is preserved in specimen BP/1/2701a (Fig. 6 I-K) and comprises a subhorizontal footplate ventrally (epft) and a rod-like ascending ramus dorsally (epar). The footplate consists of a short anterior ramus and a posterior quadrate ramus that is broken off close to its mid-length (Fig. 6J, K). The preserved portion of the quadrate ramus is taller and longer than the anterior ramus in lateral view (Fig. 6J). The ventromedial surface of the footplate rests entirely on the dorsal side of the quadrate ramus of the pterygoid as in other emydopoids (Keyser, 1973; Fourie, 1991, 1993), such that the suture between the two bones (the footplate of the epipterygoid and the quadrate ramus of the pterygoid) follows the longitudinal plane of the skull. The epipterygoid footplate does not contact the parabasisphenoid in Myosaurus. As observed in lateral view, the lateral surface of the epipterygoid is nearly flat but its medial surface is concave (Fig. 6J, K). In dorsal view, the quadrate ramus of the epipterygoid footplate is mediolaterally wider than the anterior ramus. In Myosaurus, the ascending ramus of the epipterygoid is longer and straighter than in Kaaeingasaurus, and forms a right angle with the footplate (Fig. 6J). The ascending ramus has an anteroposteriorly wide base. Dorsally, it tapers considerably to become a rod-like bone at its mid-height and broadens dorsally to form an inverted triangular dorsal process (epdp, Fig. 6J, K). The dorsal process of the ascending ramus is slightly concave medially and articulates with the parietal laterally. Parabasisphenoid: The parabasisphenoid complex of Myosaurus (pbs) is well-preserved and is subtriangular in both dorsal and ventral views (Figs 2, 6). As usual in dicynodonts, the basipostsphenoid forms the posterior end of the bone, and the parasphenoid rostrum and basipresphenoid (PRB) forms its anterior part (Cox, 1959). The PRB is mediolaterally broad in Myosaurus (length-to-width ratio 1.1 in Myosaurus vs. 1.5 in Pristerodon). In dorsal view, it is excavated by an anteroposteriorly elongated and thin sulcus (pss). This sulcus is bordered by two low lateral crests (psc, Fig. 6L). Posteriorly, this sulcus ends in a small, anteroposteriorly oval foramen in the parasphenoid (psf). This pit opens on the ventral side of the bone within a circular cavity (Fig. 6N). As this pit is located anterior to the carotid foramina in BP/1/2690 (Fig. 6L), it forms a notch on the anterior margin of the carotid foramen in BP/1/2701a and may represent a relictual pituitary fossa. In contrast to what is found in several dicynodont taxa (e.g. Niassodon), the PRB and the basipostsphenoid are fused in Myosaurus. The position of the dorsal exit of the carotid foramina gives a rough indication of the suture between the PRB and the basipostsphenoid, and these foramina open dorsally into a single large circular orifice. Posterior to the carotid foramina, in dorsal view, lies the sella turcica (stu), which is a shallow excavation bordered posteriorly by a shallow inconspicuous ridge corresponding to the dorsum sellae (Fig. 6L). The sella turcica extends a short distance anteriorly onto the carotid foramina, but it is not confined anteriorly. There is no tuberculum sellae in Myosaurus. The sella turcica in Myosaurus is limited laterally by the dorsally projecting clinoid process (clp) of the basipostsphenoid. The clinoid process sharpens dorsally, its dorsal edge is turned medially and has a concave recess along with its dorsal extension. There is a gap of 0.3 mm that separates the clinoid process from the pila antotica, and the two processes are separated posteriorly by the dorsum sellae (ds, Fig. 6L). In dorsal view, the dorsum sellae is interrupted posteriorly by the transverse suture with the basioccipital. The basisphenoidal tubera (bpt) project posteroventrally and have a slightly concave dorsal surface that articulates with the basioccipital. As such, the basisphenoidal tubera do not border the fenestra ovalis, because the anteromedial wall of the fenestra is entirely formed by the basioccipital. In lateral view, the parasphenoid rostrum is straight but has a dorsoventrally expanded anterior tip (Fig. 6M). The clinoid process is offset from the parasphenoid rostrum, forming a notch where they meet. It forms an acute angle with the parasphenoid rostrum in Myosaurus. In ventral view, the PRB tapers more anteriorly than posteriorly. It is excavated by a median trough that envelops the parasphenoid foramen (Fig. 6N). The ventral aspect of the base of the PRB is not flat but is irregular due to the interdigitating suture with the pterygoid median plate (Fig. 6N). This suture obscures most of the ventral anatomy of the PRB. The basipostsphenoid in Myosaurus does not form the ventral depression of the basicranium, which is instead composed of basioccipital. The basisphenoidal tubera border the ventral depression only laterally. The carotid foramina are bordered by thin ridges and they diverge ventrally and follow, to some degree, the basisphenoidal tubera (Fig. 6N). Basioccipital: The basioccipital (bo) in Myosaurus forms more than half the length of the braincase floor at the back of the skull (Figs 2, 7). It is subtrapezoidal in dorsal and ventral views, with the posterior wall being the shortest. Both anteriorly and posteriorly, the basioccipital forms an inverted U-shape. The basioccipital contacts the parabasisphenoid anteriorly, the opisthotic laterally, the prootic anterodorsally and the exoccipital posterodorsally. The basioccipital condyle (boc) is the most prominent structure in posterior view and is excavated by two concavities (bocc) that host the exoccipital in posterior view (Fig. 7A). Dorsal to these concavities, the condyle is traversed by an M-shaped ridge (bocdr) that articulates with the anterior tuberosity of the exoccipital (Fig. 7B). In dorsal view, the dorsal surface of the basioccipital is slightly concave (Fig. 7B). This concavity is divided by a blunt median ridge (bomr). The lateral margin of the basioccipital has sigmoidal ridges in dorsal view. The vestibule of the bony labyrinth (vea) deeply notches the lateral aspects of the basioccipital and opens ventrally as the fenestra ovalis (fo). In ventral view, the basioccipital of Myosaurus is excavated by a Y-shaped depression (bod, Fig. 7C). The two branches of the Y-shaped depression delineate the semispherical condyle posteriorly. Four nutritive foramina (bonf) aligned on the sagittal axis perforate the basioccipital along the median depression. The basioccipital contacts the parabasisphenoid anteroventrally along an undulating suture with the basisphenoidal tubera extending backward to overlap the basioccipital tubera. The fenestra ovalis is ellipsoidal (3.3 × 1.5 mm) with its long diameter extending along the coronal axis of the skull. In posterior view, there is a symmetrical pit (spi) on each side of the supraoccipital, dorsal to the foramen magnum. These have been interpreted as foramina for blood vessels bringing nutrients to the brain (Hammer & Cosgriff, 1981; Angielczyk & Kammerer, 2017) in other dicynodonts, but in Myosaurus the pits do not form a hole in the bone anteriorly. Cluver (1974b: fig. 3C) previously described the nutrient channel on the suture between the supraoccipital and the squamosal in Myosaurus, also present in BP/1/2701a. However, in specimen BP/1/2690 there are other pits located more medially within the supraoccipital (Fig 7J). Interestingly, there is a channel in Compsodon that starts in a homologous position as in BP/1/2690 but continues laterally to reach the position described by Cluver (Angielczyk & Kammerer, 2017: fig. 2). Whether these structures are part of the same system has yet to be confirmed. The supraoccipital is bounded laterally by shallow vertical depressions (svd) in posterior view that descend from the dorsal edge of the supraoccipital onto the exoccipital (Fig. 7J). The lateroventral corner of the supraoccipital forms the posttemporal fenestra together with the exoccipitals, but the lateral wall of this fenestra is bounded by the opisthotic. As in other dicynodonts, the foramen magnum is dorsoventrally oval in posterior view. In Myosaurus, the foramen magnum is 3.9 mm at its widest point. Ventrally, the supraoccipital is excavated by a conspicuous sulcus for the posterior semicircular canal (pscc, Fig. 7K). The supraoccipital has a lateral vertical recess (slr) formed by the lateral and anterior edges of the supraoccipital, best seen in dorsal view (Fig. 7L). The recess descends from the dorsalmost aspect of the supraoccipital to nearly half the height of the foramen magnum. Prootic: The prootic of Myosaurus (pr, Fig. 7) is a plate-like, vertically oriented bone in lateral and medial views, that forms the lateral wall of the braincase. As is typical in dicynodonts, the prootic borders the anterior wall of the foramen magnum. It is formed by the pila antotica anteriorly and the alar process posteriorly. The prootic of Myosaurus specimen BP/1/2690 is not completely fused to the surrounding bones (except the opisthotic) as it displays a gap of a few millimeters from the supraoccipital dorsally and the basioccipital and parabasisphenoid anteroventrally on CT images. We cannot exclude the possibility that the specimens here described are subadult (see discussion below). In anterior view, the pila antotica (pa) of Myosaurus is tall, slightly curved medially, mediolaterally compressed and tapers dorsally. Its anteroventral half is bordered by medial and lateral crests (prac) that join dorsally half way up the pila antotica, flanking a shallow vertical trough (Fig. 7M). In lateral view, the main body of the prootic sends an alar process (ap) posteriorly, which sutures with the opisthotic on its posteroventral part. The suture with the opisthotic is serrated and is oblique in lateral view (see the orientation of the right margin of the prootic where the suture is in Figure 7N). The alar process of the prootic has a sigmoid posterodorsal margin, and its dorsal and ventral margins are horizontal. Its anterior margin is straight and obliquely oriented in lateral view (Fig. 7N). A notch for the passage of the trigeminal nerve (CNV) is present at theanteroventralpartofthealarprocessandposteriortothe pila antotica. In lateral view, the pila antotica of Myosaurus appears as an isosceles triangle; the anterior border is relatively straight and the posterior border slightly convex (Fig. 7N). The pila antotica typically overlaps the clinoid process of the basisphenoid, but in BP/1/2690 they are separated by a 0.3 mm gap (gp, Fig. 7R). The medial face of the prootic is slightly depressed in lateral view (best seen in dorsal view, Fig. 7P), and ventral to this depression, the prootic is perforated by the circular facial foramen (fa). Also, the prootic forms the lateral wall of the conical fenestra ovalis which opens on the ventral side of the bone. In medial view, the posterior and anterior margins of the prootic are oblique, whereas the ventral margin is horizontal. The dorsal margin of the prootic is V-shaped as it is traversed by the trigeminal nerve (Fig. 7O). The prootic forms the anterior wall of the horizontal, large and deep floccular fossa (flo) in medial view. The dorsal and ventral limits of the floccular fossa bear conjoined sigmoidal crests (prmc), with the ventral one being the most prominent. The dorsal crest serves to articulate with the supraoccipital. The suture with the supraoccipital appears sigmoidal in medial view (see the shading in Figure 7O). A small circular cavity for the anterior semicircular canal (ascc) perforates the prootic dorsal to the floccular fossa in medial view. This canal connects to another larger cavity located ventral to the floccular fossa, which hosts the vestibule of the inner ear (ve, Fig. 7O). As the sutural area between the prootic and opisthotic is visible in medial view, it appears trapezoidal (see the grey shading in Figure 7O). The base of the pila antotica is robust in medial view, and it overlaps the basioccipital along a nearly rectangular contact (see the green shading in Figure 7O). Dorsal to this suture and anterior to the vestibule is the facial foramen. In posterior view, the prootic is excavated by a semicircular excavation (ppex), which exits through the posttemporal fenestra (Fig. 7Q). There is a bulge (prpb) at the concave part of the excavation which contributes to the anterior components of the posttemporal fenestra wall (Fig. 7Q). The prootic of BP/1/2690 is separated from the supraoccipital by a 0.4 mm gap posteriorly. Along its posteroventral corner, the prootic contacts the opisthotic in posterior view. This contact appears triangular. At the medial part of the suture, the prootic and opisthotic are perforated by the lateral semicircular canal (lscc, Fig. 7Q). In dorsal view, the prootic forms a vertical buttress (pabt) and sends the alar process laterally. This buttress hosted the anterior semicircular canal. The area between the buttress and the alar process is depressed in dorsal view (Fig. 7P). Opisthotic: The opisthotic in Myosaurus (op, Fig. 7) displays a subtrapezoidal shape in posterior view. It bears a well-developed ventromedial process. In anterior view, the lateral margin of the opisthotic forms the posteroventral wall of the posttemporal fenestra. The suture with the prootic is located in the middle of the anterior face of the opisthotic. This surface appears jagged in Figure 7S as the two bones were partially fused as in most dicynodonts, and was thus d, Published as part of Macungo, Zanildo, Benoit, Julien, Fernandez, Vincent & Araújo, Ricardo M N, 2023, X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny, pp. 1-46 in Zoological Journal of the Linnean Society 198 (1) on pages 13-20, DOI: 10.1093/zoolinnean/zlac033, http://zenodo.org/record/7922143, {"references":["Haughton SH. 1917. Investigations in South African reptiles and amphibia. Annals of the South African Museum 12: 164 - 172.","Castanhinha R, Araujo R, Junior LC, Angielczyk KD, Martins GG, Martins RM, Chaouiya C, Beckmann F, Wilde F. 2013. Bringing dicynodonts back to life: paleobiology and anatomy of a new emydopoid genus from the Upper Permian of Mozambique. PLoS One 8: e 80974.","Hammer WR, Cosgriff JW. 1981. Myosaurus gracilis, an anomodont reptile from the Lower Triassic of Antarctica and South Africa. Journal of Palaeontology 55: 410 - 424.","Cluver MA. 1974 b. The cranial morphology of the Lower Triassic dicynodont Myosaurus gracilis. Annals of the South African Museum 66: 35 - 54.","Keyser AW. 1973. A preliminary study of the type area of the Cistecephalus Zone of the Beaufort Series, and a revision of the anomodont family Cistecephalidae. Geological SurVey of South Africa 62: 1 - 71.","Keyser AW. 1974. Evolutionary trends in Triassic Dicynodontia (Reptilia Therapsida). Palaeontologia Africana 17: 57 - 68.","Angielczyk KD, Sullivan C. 2008. Diictodon feliceps (Owen, 1876), a dicynodont (Therapsida, Anomodontia) species with a Pangaean distribution. Journal of Vertebrate Paleontology 28: 788 - 802.","Angielczyk KD, Kammerer CF. 2017. The cranial morphology, phylogenetic position and biogeography of the Upper Permian dicynodont Compsodon helmoedi Van Hoepen (Therapsida, Anomodontia). Papers in Palaeontology 3: 513 - 545.","Laass M, Kaestner A. 2017. Evidence for convergent evolution of a neocortex-like structure in a Late Permian therapsid. Journal of Morphology 278: 1033 - 1057.","Angielczyk KD, Benoit J, Rubidge BS. 2019. A new tusked cistecephalid dicynodont (Therapsida, Anomodontia) from the Upper Permian Upper Madumabisa Mudstone Formation, Luangwa Basin, Zambia. Papers in Palaeontology 7: 405 - 446.","Fourie H. 1991. A detailed description of the skull of Emydops (Therapsida: Dicynodontia). Master's Thesis, University of the Witwatersrand.","Fourie H. 1993. A detailed description of the internal structure of the skull of Emydops (Therapsida: Dicynodontia). Palaeontologia Africana 30: 103 - 111.","Cox CB. 1959. On the anatomy of a new dicynodont genus with evidence of the position of the tympanum. Procedings of the Zoological Society of London 132: 321 - 367."]}

PRISTERODON MACKAYI HUXLEY, 1868 Specimen: BP/1/2642. In the present study, Pristerodon is used as the outgroup taxon for comparison with the emydopoids because it displays the more generalized anatomy of basal dicynodonts (Barry, 1967; Cluver & King, 1983; Keyser, 1993; King & Rubidge, 1993; Ray, 2001; Modesto, 2003; Angielczyk, 2007; Laass, 2015). Orbitosphenoid: The orbitosphenoid is a verticallyoriented bone located at the skull midline (Figs 1, 2B, 3). It contacts the frontal and parietal dorsally and the parabasisphenoid complex ventrally and supports the olfactory bulbs in life (Hopson, 1979). Its exact anatomical constituents have been heavily debated (Olson, 1938, 1944; Barry, 1967; Kemp, 1969; Cluver, 1971), but it is generally agreed that the orbitosphenoid consists of two dorsally projecting wings and a medial vertical crest (the mesethmoid) in non-mammalian synapsids (Araújo et al., 2017; Angielczyk et al., 2019). However, the homology between the orbitosphenoid of therapsids and the sphenethmoid of other amniotes remains uncertain. The orbitosphenoid of Pristerodon conforms to the typical synapsid pattern, displaying a characteristic Y-shaped cross-section (Laass, 2015). In anterior view, the wings of the orbitosphenoid (obw) are curved, which results in a slightly convex outer wall, making an angle of 48° with the sagittal plane (Fig. 3A). Anterodorsally, the median vertical process (obvp) projects dorsally and divides the olfactory cavity medially (ofc). The median vertical process is slender at its midheight but has expanded dorsal and ventral edges in anterior view (Fig. 3A). At its dorsalmost part, the median vertical process forms a broad horizontal surface (hpl) that contacts the frontal anterodorsally. This articulation surface is oval in dorsal view (Fig. 3B). The wings of the orbitosphenoid are thin anteriorly but are thicker posteriorly (Fig. 3B). In dorsal view, the wings of the orbitosphenoid form a long anteroposterior gutter that host the olfactory bulbs (Fig. 3B). In lateral view, the orbitosphenoid has a subtrapezoidal outline. The dorsal margin of the wings is horizontal in lateral view, except for a notch that excavates the wings at midlength (obdn, Fig. 3C). The ventral margin of the mesethmoid articulates with the dorsal groove of the parasphenoid rostrum. In lateral view, the mesethmoid extends posteriorly as a wall (mpw) that supports the dorsal wings (Fig. 3C). Pterygoid: In Pristerodon, the pterygoids (pt) form an important part of the palate and display the typical dicynodont X-shaped morphology in ventral view (Figs 2D, 3). The median plate sends out divergent anterior palatal and posterior quadrate rami that form an angle of 115° between the two rami, measured on the lateral surface of the pterygoid. The palatal and quadrate rami of the pterygoid form an angle of 18° and ~56° with the anteroposterior median axis of the skull, respectively. The median plate of the pterygoid forms an interdigitated suture with the parabasisphenoid internally, but this suture has an M-like outline in ventral view (Fig. 3F). The pterygoid bounds the narrow and long interpterygoid vacuity just anterior to the median plate, and in this taxon the vacuity is bounded anteriorly by the vomer (Barry, 1967; Cluver & King, 1983; Keyser, 1993). The pterygoid in BP/1/2642 has several cracks which hampers the description of the complete morphology of the quadrate ramus (Fig. 3E, F). However, as illustrated by other specimens of Pristerodon (e.g. BP/1/7206, BP/1/3024), the quadrate ramus of BP/1/2642 is thin and laterally compressed, similar to most dicynodonts. In dorsal view, there is a small anteromedial process (pt amp, Fig. 3E) that develops on the dorsal edge of the palatal ramus of the pterygoid in BP/1/2642, similar to that described as the anterior pterygoidal process in SAM-PK-10153 by Cluver & King (1983) [but it is not the ‘anterior pterygoid blade’ of Cluver (1974b), which referred to the anterior tip of the palatal ramus more generally]. The two processes nearly touch each other at the midline and contact the vomer medially (Cluver & King, 1983). The anteromedial pterygoid process is separated from the rest of the anterior ramus by an anteroposterior notch (pt nt, Fig. 3E). The pterygoid median plate is overlapped dorsally by the laterally expanded basisphenoid. In lateral view, the palatal ramus is dorsoventrally taller anteriorly than it is posteriorly. This ramus presents a lateral process (ptlp) on its anteroventral region (Fig. 3H). The divergence of the anteromedial process gives a Y-shape to the palatal ramus in lateral view. The median plate expands laterally, forming the short and stout pterygoid lateral lamina (ptll). The pterygoid lamina is bordered by a sulcus dorsally (pt dsu, Fig. 3H). The quadrate ramus is considerably narrower than the palatal ramus. It projects posteriorly and reaches the medial side of the quadrate. A small triangular portion of the epipterygoid footplate (epi) is discernible on the left quadrate ramus (Fig. 3H). Due to damage, we could not determine how much of the epipterygoid overlaps the quadrate ramus of the pterygoid. The anterior margin of the palatal ramus is U-shaped in ventral view. Because a lamina is present dorsolaterally (ptll), the pterygoid median plate is wider posteriorly than the anterior ramus in Pristerodon. There is a trough medial to the pterygoid lamina that tapers posteriorly and anteriorly in ventral view (ptvt, Fig. 3F). This excavation is delimited medially by the prominent crista oesophagea (co), which is composed of a pair of anteroposteriorly oriented ridges in BP/1/2642. A deep, elongate anteroposterior furrow (fu) is present posteriorly between these ridges (Fig. 3F). This furrow is not visible in better-preserved specimens of Pristerodon (e.g. BP/1/3024, BP/1/7206, SAM-PK-10153 and USNM 23580), where the two sides of the crista oesophagea are fused into a single, thin median ridge. Exposure of the furrow and demarcation of the component ridges in BP/1/2642 can be attributed to damage incurred through acid preparation of this specimen (C.F. Kammerer, pers. comm.). Parabasisphenoid: The parabasisphenoid complex (pbs) forms the anterior floor of the braincase (Figs 2, 3). The parabasisphenoid in BP/1/2642 has many minute cracks, but a small portion of the parasphenoid rostrum (ps) is present together with the basipresphenoidal region (anterior to the pituitary fossa) and its basipostsphenoid portion (posterior to the pituitary fossa). The basipostsphenoid portion in Pristerodon protrudes posteroventrally and overlaps the basioccipital forming the basal tubera, and encloses the carotid foramina more anteriorly as in other dicynodonts (Modesto et al., 2003; Castanhinha et al., 2013). Along its dorsal aspect, the basipostsphenoid hosts the pituitary gland posterior to the sella turcica. In Pristerodon, the complex formed by the parasphenoid rostrum and basipresphenoid (PRB complex) is slender, tapers posteriorly and in dorsal view has an anteroposterior groove (psgr) on its anterodorsal portion (Fig. 3I). The posterior half of the PRB bears a tall process of triangular outline in lateral view (Fig. 3J). In dorsal view, the Pristerodon basipostsphenoid flares laterally from the posterior end of the parasphenoid rostrum (Fig. 3I). It is excavated by a subvertical concavity (bpdc), which is delineated ventromedially by the tuberculum sellae (tse). The left and right tuberculum sellae meet on the midline anterior to the sella turcica and continue towards the border with the parasphenoid rostrum.The tuberculum sellae marks the anterior border of the sella turcica (stu, Fig. 3I). The base of the pituitary fossa (sella turcica) is perforated by the carotid foramina (ic) and is bordered laterally by a discrete clinoid process (clp). The clinoid processes (Fig. 3I, J) consist of thin crests that give a triangular outline to the pituitary fossa in dorsal view. Posterior to the pituitary fossa, the dorsum sellae (ds) forms a low tuberosity. The carotid foramina do not join dorsally into a single orifice. The carotid foramina in Pristerodon are oval with the longest diameter extending anteroposteriorly in ventral view (Fig. 3K). The distance between the two internal carotid foramina in ventral view is narrow in Pristerodon (1.2 mm). In ventral view, the basipostsphenoid contacts the basioccipital posteriorly along a sigmoidal suture and, the pterygoid anteriorly along an interdigitated M-shape suture. There is an anteroposterior sulcus with a lobate shape on the posterior median end of the basipostsphenoid, delimited by the basisphenoidal tubera laterally (bpvsu, Fig. 3K). This sulcus is 3.5 mm wide and extends posteriorly onto the basioccipital. The posteroventrally projected basisphenoidal tubera (bpt) form buttress-like structures that broaden ventrally, where they form a wall being excluded from the fenestra ovalis posteriorly. Basioccipital: The basioccipital (bo) in Pristerodon forms the posterior portion of the braincase floor, posterior to the parabasisphenoid complex (Figs 2, 4). The basioccipital in Pristerodon is expanded mediolaterally but tapers anteriorly and posteriorly, resulting in a subhexagonal shape in both ventral and dorsal views. The basioccipital can be divided into two main anatomical subunits: the basioccipital portion of the occipital condyle posteriorly and the basioccipital tubera anterolaterally. In posterior view, the basioccipital displays an inverted U-shape with the tubera pointing ventrally. As in other dicynodonts, the basioccipital in Pristerodon forms the ventral lobe of the occipital condyle and extends laterally to border the vestibule (fenestra ovalis) and the jugular foramen medially. In posterior view, the basioccipital condyle (boc) is less prominent than the exoccipital condyles (Figs 3G, 4A), and its dorsal portion flares out laterally to form two symmetrical concavities (bocc) in which the exoccipital condyles are hosted (Fig. 4A). The two concavities are separated by a median ridge (bocr) on the dorsal face of the basioccipital condyle. There is an occipital pit at the intersection between the basioccipital and exoccipital condyles in posterior view. In dorsal view, the basioccipital tubera portion is outlined by two anteriorly conjoined sigmoid ridges (bosr) that terminate posteriorly, contacting the opisthotic and bordering the medial wall of the fenestra ovalis (fo, Fig. 4B). These ridges meet anteriorly to form the anteroposteriorly oriented median ridge of the basioccipital (bomr). The basioccipital median ridge is thinner than the sigmoid ridges and is present only on the anteriormost region of the basioccipital. In dorsal view, the dorsal suture of the basioccipital condyle in Pristerodon is marked by a stretched M-shaped flat edge (ms) that smoothly develops ventrally to accommodate the exoccipital condyles (Fig. 4B). The jugular foramen (jf) opens a hemicylindrical sulcus between the M-shaped suture and the sigmoid ridge as the basioccipital forms its floor in dorsal view. In Pristerodon, only a small portion of the basioccipital contributes to the jugular foramen laterally compared to the exoccipital and opisthotic. In ventral view, the basioccipital tubera have a smoothly excavated anteroventral surface that contacts the basisphenoidal tubera. They are separated by a deeper and wider anteroposteriorly oriented midline trough (bovtr) thatopensposteriorly (Fig.4C).Thistrough is interrupted posteriorly by a low and blunt eminence, in a similar position to the intertuberal ridge (itr) of some other dicynodonts. Previous works on Pristerodon (Huxley, 1868; Broom, 1915; Barry, 1967; Cluver & King, 1983) do not comment on the presence of this ridge on the basioccipital, and this structure is so weakly developed in BP/1/2642 that is should not be considered a true intertuberal ridge of the sort seen in Lystrosaurus (e.g. NMQR 3593; NMQR 815; NM C299). In Lystrosaurus and most other taxa where the intertuberal ridge is coded as present (see, e.g. Angielczyk et al., 2021), the intertuberal ridge is a tall, clearly demarcated structure comparable in height to the basal tubera. Posterior to the low, intertuberal eminence in BP/1/2642, there is a deeper, collar-like basioccipital excavation (bocex) that separates the basioccipital tubera from the basioccipital condyle. The basioccipital condyle in BP/1/2642 is spherical and is pierced by minute foramina (bocf) in ventral view. The fenestra ovalis (fo) is oval and its long axis extends mediolaterally. In lateral view, the basioccipital tuber projects obliquely ventral to the horizontal plane, and its walls are thicker anteriorly than posteriorly (Fig. 4D). In lateral view, the vestibule of the inner ear (ve) excavates a conical cavity on the basioccipital lateral wall (fo, Fig. 4D). Exoccipital: The exoccipitals (eo) form the posterolateral portion of the braincase and constitute most of the ventral half of the foramen magnum and the dorsal two-thirds of the occipital condyle in most dicynodonts, including Pristerodon (Figs 3, 4; Cox, 1965; Modesto et al., 2003; Fröbisch, 2007; Castanhinha et al., 2013). Each exoccipital forms the medial border of the jugular foramen. Typically, the exoccipital is traversed by the canal for the hypoglossal cranial nerve (CN XII) in dicynodonts (Castanhinha et al., 2013), but this could not be segmented in the specimen BP/1/2642 due to damage. The exoccipital contacts the supraoccipital dorsally, the opisthotic laterally and the basioccipital ventrally. The exoccipital is co-ossified to the supraoccipital and opisthotic anteriorly. The ventral suture with the basioccipital is W-shaped. The exoccipital in Pristerodon can be divided into two main components: the exoccipital condyle (eoc) and the dorsal component (eodc). In anterior view, each exoccipital is knob-like and is excavated by the jugular foramen (Fig. 4E). The exoccipital condyle is robust and sends a short tuber-like process (eoat) that overlaps the M-like posterodorsal edge of the basioccipital (Fig. 4E). The base of the exoccipital condyle shows a sigmoidal outline in anterior view. The articular surface of the exoccipital condyle is convex. The dorsal component of the exoccipital has an expanded dorsal end at the contact with the supraoccipital in anterior view. The exoccipital forms the posterodorsal border of the jugular foramen (jf), which is located between the dorsal edge of the dorsal component and the exoccipital condyle in anterior view (Fig. 4E). The foramen excavates a semicylindrical cavity in the exoccipital. In posterior view, the foramen magnum (fm) is vertically elliptical and the exoccipital covers 40% of its ventral portion (Figs 2, 3). The exoccipital is dorsoventrally short in posterior view (Figs 3G, 4F). The dorsal end of the exoccipital in posterior view coincides with the greater width of the foramen magnum, which is 6 mm wide. The exoccipital condyle is typically reniform in dicynodonts but it is damaged in BP/1/2642. Therefore, the exoccipital condyle of BP/1/2642 is formed by an oblique bulge (eobg) that is overlapped by the subvertical buttress (eobt) of the dorsal component. Although the proatlas is not preserved, it is possible that this buttress could have served as an articular surface for this portion of the atlantal arch. The dorsal component forms a subvertical and hourglass-shaped buttress (eobt) that sutures with the supraoccipital dorsally and descends to overlap the exoccipital condyle. The dorsal component extends dorsally to just above the level of the dorsal margin of the jugular foramen. The two exoccipitals are co-ossified at the midline above the basioccipital (Fig. 3G). Supraoccipital: The supraoccipital (su) is the largest element of the occiput, forming the posterodorsal part of the braincase (Figs 2, 3). The supraoccipital in Pristerodon is subvertically oriented with a slight anterior tilt (Fig. 4I). Pristerodon shows the typical anatomy of the dicynodont supraoccipital, which is divided into three main anatomical subunits (e.g. Castanhinha et al., 2013; Macungo et al., 2020): one medial lobe and two lateral alae. The supraoccipital bounds the dorsal half of the foramen magnum. Its lateral wing borders the posttemporal fenestra dorsally, and hosts the posterior half of the floccular fossa and the vestibular organ medially. Anteriorly, the supraoccipital contacts the prootic and ventrally the opisthotic and exoccipital. In anterior view, the supraoccipital in Pristerodon is characterized by two anteriorly projected crests (sap, Fig. 4G, I) that lengthen ventrally in contact with the dorsal process of the prootic. These crests are oblique and meet dorsally at the midline. They border an anteromedial triangular recess (sar) that is bounded ventrally by an incipient horizontal ridge (sor). Although Laass (2015) and Laass et al. (2017) identified the ‘unossified zone’, this structure is dorsal to the supraoccipital. The anteromedial triangular recess is located on the anterior surface of the supraoccipital, therefore we cannot elaborate on the ‘unossified zone’. The anterior face of the supraoccipital lateral alae is perforated by small circular oblique cavities that accommodate the anterior semicircular canal (ascc) in anterior view. These cavities communicate internally to the large vertical one that accommodates the crus communis (cca, Fig. 4G, H). This region accommodating the crus communis does not form a distinct buttress in Pristerodon, unlike in emydopoids. Mediolaterally, the supraoccipital forms the posterior wall of the floccular fossa (flo), which has a circular outline and is 2.65 mm deep (Fig. 4G, H). The anterior suture with the prootic is located at the top of a dorsoventrally elongated recess (slr, Fig. 4I, J) in lateral view. This suture is dorsoventrally oriented and appears completely co-ossified on CT images. The dorsoventral recess is also known as the venous groove in Dicynodontoides and other dicynodonts (Olson, 1944; Cox, 1959; Cluver, 1971; King, 1981; Surkov & Benton, 2004) or as the anterior posttemporal fenestra groove in Emydops (Fröbisch & Reisz, 2008). This recess is dorsoventrally oblique and as tall as the supraoccipital. In posterior view, the supraoccipital of Pristerodon is tall as it forms 60% of the dorsal margin of the elliptical foramen magnum (Fig. 3G). The supraoccipital medial lobe is robust and has a rounded dorsal margin in occipital view (Fig. 3G). The supraoccipital alae of Pristerodon are laterally pointed and possess a horizontal process (spp), which expands laterally to border the dorsal margin of the posttemporal fenestra (ptf, Fig. 3G). The suture between the supraoccipital and the exoccipital is oblique in posterior view and is horizontal between the supraoccipital and the opisthotic (Fig. 3G). Prootic: The prootic (pr) forms the anterior part of the braincase lateral wall and borders the foramen magnum anterolaterally (Figs 2, 5). Its medial wall is excavated by the floccular fossa and is pierced by the anterior semicircular canal. Due to its complex, Published as part of Macungo, Zanildo, Benoit, Julien, Fernandez, Vincent & Araújo, Ricardo M N, 2023, X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny, pp. 1-46 in Zoological Journal of the Linnean Society 198 (1) on pages 6-12, DOI: 10.1093/zoolinnean/zlac033, http://zenodo.org/record/7922143, {"references":["Huxley TH. 1868. On Saurosternon bainii and Pristerodon mckayi, two new fossil lacertilian reptiles from South Africa. Geological Magazine 5: 201 - 205.","Cluver MA, King GM. 1983. A reassessment of the relationships of Permian Dicynodontia (Reptilia, Therapsida) and a new classification of dicynodonts. Annals of the South African Museum 91: 195 - 273.","Keyser AW. 1993. A re-evaluation of the smaller Endothiodontidae. Memoir of Geological SurVey of South Africa 82: 1 - 53.","King GM, Rubidge BS. 1993. A taxonomic revision of small dicynodonts with postcanine teeth. Zoological Journal of the Linnean Society 107: 131 - 154.","Ray S. 2001. Small Permian dicynodonts from India. Palaeontological Research 5: 177 - 191.","Modesto S, Rubidge B, Visser I, Welman J. 2003. A new basal dicynodont from the Upper Permian of South Africa. Palaeontology 46: 211 - 223.","Angielczyk KD. 2007. New specimen of the Tanzanian dicynodont ' Cryptocynodon ' parringtoni Von Huene, 1942 (Therapsida, Anomodontia), with an expanded analysis of Permian dicynodont phylogeny. Journal of Vertebrate Paleontology 27: 116 - 131.","Hopson JA. 1979. Paleoneurology. Biology of the Reptilia & Gans C Neurology A. Eds. New York: Academic Press. 9: 39 - 146.","Olson EC. 1938. The occipital, otic, basicranial and pterygoid regions of the Gorgonopsia. Journal of Morphology 62: 141 - 175.","Olson EC. 1944. The origin of mammals based upon the cranial morphology of the therapsid suborders. Geological Society of America Special Papers No. 55. Boulder: The Geological Society of America.","Kemp TS. 1969. On the functional morphology of the gorgonopsid skull. Philosophical Transactions of the Royal Society of London 256: 1 - 83.","Cluver MA. 1971. The cranial morphology of the dicynodont genus Lystrosaurus. Annals of the South African Museum 56: 155 - 274.","Araujo R, Fernandez V, Polcyn MJ, Frobisch J, Martins RMS. 2017. Aspects of gorgonopsian paleobiology and evolution: insights from the basicranium, occiput, osseous labyrinth, vasculature, and neuroanatomy. PeerJ 5: e 3119.","Angielczyk KD, Benoit J, Rubidge BS. 2019. A new tusked cistecephalid dicynodont (Therapsida, Anomodontia) from the Upper Permian Upper Madumabisa Mudstone Formation, Luangwa Basin, Zambia. Papers in Palaeontology 7: 405 - 446.","Cluver MA. 1974 b. The cranial morphology of the Lower Triassic dicynodont Myosaurus gracilis. Annals of the South African Museum 66: 35 - 54.","Castanhinha R, Araujo R, Junior LC, Angielczyk KD, Martins GG, Martins RM, Chaouiya C, Beckmann F, Wilde F. 2013. Bringing dicynodonts back to life: paleobiology and anatomy of a new emydopoid genus from the Upper Permian of Mozambique. PLoS One 8: e 80974.","Broom R. 1915. On the anomodont genera, Pristerodon and Tropidostoma. Proceedings of the Zoological Society of London 1915: 355 - 361.","Angielczyk KD, Liu J, Yang W. 2021. A redescription of Kunpania scopulusa, a bidentalian dicynodont (Therapsida, Anomodontia) from the? Guadalupian of northwestern China. Journal of Vertebrate Paleontology 41: e 1922428.","Cox B. 1965. New Triassic dicynodonts from South America, their origins and relationships. Philosophical Transactions of the Royal Society of London B 248: 457 - 514.","Frobisch J. 2007. The cranial anatomy of Kombuisia frerensis Hotton (Synapsida, Dicynodontia) and a new phylogeny of anomodont therapsids. Zoological Journal of the Linnean Society 150: 117 - 144.","Macungo ZA, Loide I, Zunguza S, Nhamutole N, Maharaj IEM, Mugabe J, Angielczyk KD, Araujo R. 2020. Endothiodon (Therapsida, Anomodontia) specimens from the Middle / Late Permian of the Metangula Graben (Niassa Province, Mozambique) increase complexity to the taxonomy of the genus. Journal of African Earth Science 163: 103647.","Cox CB. 1959. On the anatomy of a new dicynodont genus with evidence of the position of the tympanum. Procedings of the Zoological Society of London 132: 321 - 367.","King GM. 1981. The functional anatomy of a Permian dicynodont. Philosophical Transactions of the Royal Society of London B 291: 243 - 322.","Surkov MV, Benton MJ. 2004. The basicranium of the dicynodonts (Synapsida) and its use in phylogenetic analysis. Palaeontology 47: 619 - 638.","Frobisch J, Reisz RR. 2008. A new species of Emydops (Synapsida, Anomodontia) and a discussion of dental variability and pathology in dicynodonts. Journal of Vertebrate Paleontology 28: 770 - 787."]}

CISTECEPHALIDAE BROOM, 1903 Specimen: DMMM-PK-16-1. Orbitosphenoid: Specimen DMMM-PK-16-1 does not have the orbitosphenoid preserved. Pterygoid: The pterygoid of the Malawian cistecephalid DMMM-PK-16-1 (pt) has both the palatal and quadrate rami well preserved but they are riddled by several small breaks and cracks (Figs 2, 8). Its morphology is the typical dicynodont X-shape in dorsal and ventral views. The palatal rami (aptr) are parallel on their posterior half and diverge laterally in the anterior direction. Although most similar to Cistecephaloides, this condition is different from all cistecephalids in which the anterior rami are divergent along their entire length. However, it is important to note that the pterygoids are typically much exposed to taphonomic damage in almost all dicynodonts, so this comparison should be taken with caution. In DMMM-PK-16-1, the quadrate rami (ptqr) diverge at an angle of 117°, whereas the palatal rami form an angle of ~29° with the anteroposterior median axis of the skull. Both palatal and quadrate rami of the pterygoid diverge at an angle of ~83°, measured on the lateral surface of the pterygoid. The Malawian cistecephalid has no pterygoid anteromedial process dorsally. In dorsal aspect, the palatal rami of the pterygoid are shorter and mediolaterally wider than the quadrate rami (Fig. 8A). The quadrate ramus of the pterygoid reaches the quadrate posteriorly and curves slightly medially in ventral view (Fig. 8C). In lateral view, the palatal ramus is dorsoventrally taller than the quadrate ramus in the Malawian cistecephalid DMMM-PK-16-1, but the quadrate ramus is mediolaterally narrow. The lateral aspect of the quadrate ramus of the pterygoid is excavated by a shallow anteroposterior trench (pt ltr) that accommodates the epipterygoid footplate (Fig. 8B). In DMMM-PK-16-1, the two pterygoids are separated medially by the parabasisphenoid to which is co-ossified posteriorly. The pterygoid of the Malawian cistecephalid does not form a distinct median plate per se, as the rami do not meet on the midline. There is considerable variation on how the pterygoids meet at the median pterygoid plate in cistecephalids [see Angielczyk et al. (2019) for further discussion of this variation]. However, in the Malawian cistecephalid DMMM-PK-16-1, the two pterygoids are separated by a thin crest emerging from the parasphenoid, a condition shared with Cistecephaloides (Cluver, 1974a), but contrasting with the condition seen in Cistecephalus, Kaaeingasaurus, Kembaaeacela and Sauroscaptor (Cox, 1972; Keyser, 1973; Kammerer et al., 2016; Angielczyk et al., 2019). In lateral view (Fig. 8B), the basioccipital tubera slope almost vertically and their anterior wall is thicker than the posterior one. The basioccipital tubera form the medial wall of the fenestra ovalis. The fenestra ovalis is elliptical and is oriented obliquely, and its largest diameter is 2.3 mm. The basioccipital makes a small contribution to the medial border of the jugular foramen in the Malawian cistecephalid. Most of the ventral anatomy of the basioccipital is damaged in DMMM-PK-16-1. The remaining features are the wide medial depression (bod) that separates the basioccipital tubera anteriorly, and delineates the basioccipital condyle posteriorly (Fig. 8C). The ventral depression of the basioccipital reaches the S-like suture with the basisphenoid anteriorly. It appears slightly deeper than the dorsal one, despite this region being damaged. In ventral view, the basioccipital condyle is subtriangular with a wide base forming the posterior margin (Fig. 8C). Exoccipital: The exoccipital forms the dorsal portion of the occipital condyle and extends dorsally to form the foramen magnum lateral walls (Fig. 8). As it is damaged, the exoccipital appears knob-like in shape in both anterior and posterior views. Anteriorly, the exoccipital condyle bears a subvertical tuberosity (eoat) that laterally flanks the jugular foramen (jf) and forms the anterior articular surface of the condyle (Fig. 8D). The exoccipital condyle has a flat anterior surface caused by erosion. Little can be said about the anterior face of the dorsal component due to damage, except that it has a lobate outline. The exoccipital condyles are severely damaged in this specimen such that their midline contact has been broken. However, the sulcus on the posterior surface of the basioccipital condyle suggests that the left and right exoccipitals met medially as in other cistecephalids (Keyser, 1973; Cluver, 1974a; Angielczyk et al., 2019). The left exoccipital is better preserved dorsally and its dorsal portion forms a D-shaped structure (eodc, Fig. 8E) in posterior view. The exoccipital dorsal component forms a convex suture with the opisthotic and supraoccipital laterally. This component is connected to the exoccipital condyle by a shallow exoccipital sulcus (eopsu) in posterior view (Fig. 8E). Medially, the right exoccipital condyle is pierced by two conspicuous foramina for the hypoglossal nerve and maybe an accompanying vessel (hf), which are separated ventrally by a thin crest (Fig. 8F). The two foramina are oriented obliquely, and the lateral one is the largest. The lateral foramen is oval and its major diameter is 0.3 mm, whereas the medial foramen is circular with a diameter of 0.1 mm. Supraoccipital: The supraoccipital (su) shows the typical anteroposterior shortening and transverse widening of the skull in cistecephalid dicynodonts (Keyser, 1973; Cluver, 1974a; Kammerer et al., 2016; Angielczyk et al., 2019) and has a saddle shape in posterior view (Fig. 8O). In specimen DMMM-PK-16-1, the supraoccipital is eroded around the medial lobe and the dorsal portion of the left ala. The supraoccipital surrounds the dorsal half of the foramen magnum, but the dorsal margin of the foramen could not be delimited in this specimen because of damage. The supraoccipital contacts the exoccipital ventromedially along an oblique suture and the opisthotic ventrally along a horizontal suture. It contacts the prootic anteriorly along a suture parallel to the coronal plane observed in lateral view. In anterior view, the anterodorsal portion of the medial lobe has two anteroposteriorly and dorsoventrally short descending processes (sap) that probably delimited the hindbrain in life as in Kaaeingasaurus (Fig. 8M). The right process is deflected at its base and forms a notch with the anterior face of the supraoccipital ala, and also forms the anterodorsal border of the foramen magnum. The supraoccipital ala has a bulge anteriorly which makes up the posterodorsal wall of the large and deep floccular fossa (flo) in DMMM-PK-16-1. This bulge is also penetrated by the bony enclosure of the anterior semicircular canal (ascc) just dorsal to the floccular fossa (flo) and by the crus communis (cc) on the posterolateral edge of the floccular fossa (Fig. 8M). Laterally, the supraoccipital ala is excavated by the lateral recess (slr, Fig. 8P), which is flanked by the supraoccipital posteriorly and leads to the posttemporal fenestra. In posterior view, the medial lobe of the supraoccipital expands dorsally toward the top of the skull and has a semicircular depression on its median posterodorsal region (ssd, Fig. 8O). The lateral alae of the Malawian cistecephalid DMMM-PK-16-1 supraoccipital are more extended and pointed laterally, and form the entire dorsal border of the posttemporal fenestra in posterior view (Fig. 8O). The suture with the exoccipital is located anteriorly in the recess for the posterior semicircular canal (pscc). Prootic: The prootic (pr) is well preserved in DMMM-PK-16- 1 comprising the alar process posteriorly and the anterodorsally directed pila antotica (pa) (Fig. 8 G-L). As is typical in dicynodonts, the prootic of DMMM-PK-16-1 forms the anterolateral wall of the braincase as it borders the foramen magnum anteriorly. Contrary to the situation in Kaaeingasaurus, the prootic in DMMM-PK-16-1 is strongly co-ossified to only the supraoccipital and opisthotic, but a gap of 0.2 mm separates it from the basioccipital and basisphenoid (gap, Fig. 8G). In anterior view, the prootic is gently twisted medially in the Malawian cistecephalid. Its alar process (ap) expands laterally in anterior view, resulting in a concave lateral margin of the bone (Fig. 8H). The dorsal edge of the alar process of the prootic is slightly pointed and extends dorsally in anterior view.The right pila antotica is best preserved in DMMM-PK-16-1. In anterior view, the pila antotica is dorsoventrally thin and mediolaterally compressed on the dorsal side when compared to the remaining taxa described here. The dorsalmost part of the pila antotica is bent laterally in anterior view (Fig. 8H). Its anteroventral part is broad as it overlaps the parabasisphenoid. This overlay is not sutural as the two bones are separated by a ~ 0.5 mm gap. As observed laterally, the pila antotica is obliquely oriented, tall and tapers dorsally. The lateral face of the pila antotica ventral to the trigeminal notch is depressed. In lateral view, the prootic appears U-shaped. The alar process and the pila antotica are separated by the trigeminal notch (tgn, Fig. 8I), which is wider in the Malawian cistecephalid and Kaaeingasaurus than in Myosaurus and Pristerodon. The alar process of the prootic tapers dorsally in lateral view, and it is widest at mid-height. Whereas the lateral margin of the prootic forms an oblique suture with the opisthotic, its ventral margin forms a horizontal contact with the basioccipital in lateral view (Fig. 8I). Dorsal to the suture with the opisthotic, the prootic forms the anterior border of the posttemporal fenestra (ptf). The fenestra ovalis (fo) is formed at the intersection of the prootic-opisthotic-basioccipital, and the prootic forms its anterior border. Ventrally, the prootic is perforated by the facial foramen which is located dorsal to the fenestra ovalis (Fig. 8I). In medial view, the floccular fossa (flo) excavates the internal aspect of the prootic horizontally (Fig. 8J). The prootic forms about 60% of its anterior margin. The floccular fossa is 1.6 mm deep in DMMM-PK-16-1. The portion of the prootic that forms the floor of the floccular fossa is blade like (pbl) in medial view (Fig. 8J). This blade-like process roofs the vestibular cavity and separates it from the floccular fossa. In DMMM-PK-16-1, the vestibule (ve) is large, inflated and vertically oriented as in other cistecephalids (Laass & Schillinger, 2015; Laass & Kaestner, 2017; Angielczyk et al., 2019). The prootic has a thicker aspect dorsal to the floccular fossa, where it is excavated by a small circular cavity for the anterior semicircular canal (ascc, Fig. 8J). In ventral view, the prootic forms a concave contact with the basioccipital and parabasisphenoid. The facial foramen in DMMM-PK-16-1 is small, circular and excavates the prootic vertically in ventral view (Fig. 8K). The vestibule of the Malawian cistecephalid is conical when observed ventrally. In posterior view, the prootic has a convex lateral margin. Its dorsomedial margin is knob-like but the ventromedial one is nearly oblique (Fig. 8L). At its mid-height, the prootic bears a horizontal blade-like process (pbl) that sutures with the supraoccipital and opisthotic. Dorsal to the blade, the prootic sutures with the supraoccipital, and ventral to the blade it sutures with the opisthotic. Also, the vestibule of the inner ear is visible ventral to the blade in posterior view (Fig. 8L). The lateral semicircular canal (lscc) perforates the prootic and opisthotic immediately ventral to the horizontal blade-like process. Opisthotic: The opisthotic of the Malawian cistecephalid (op) is hourglass shaped in anterior and posterior views and its dorsal and ventral margins are concave (Fig. 8 M-P). It can be divided into two subunits: the ventromedial process and the main body medially that sends two crests laterally. The opisthotic bears an anterior projection that houses the vestibule (Fig. 8M, N). This bulge (obg) serves as a sutural part with the prootic anteriorly. On its dorsal margin, the opisthotic bulge is perforated by a cavity for the lateral semicircular canal (lscc). This cavity connects to the vestibule (ve) on the anteromedial surface of the opisthotic. The vestibule is spherical and inflated as is typical for cistecephalids and excavates a shallow concavity on the anterior face of the ventromedial process of the opisthotic (Fig. 8M). The vestibule is anteroventrally bordered by a V-like low crest (oac). The opisthotic seems to have housed only 40% of the vestibule leaving the other 60% to the prootic. Lateral to the bulge, the face of the opisthotic bears a vertical depression (oad) for articulation with the medial side of the quadrate-quadratojugal complex. The recess for the lateral semicircular canal (lssc) of DMMM-PK-16-1 is small and oval in internal view (Fig. 8N). At its ventralmost margin, the vestibule opens into a large elliptical fenestra ovalis, observed in ventral view. In posterior view, the main body is a horizontal bulge-like process (opp, Fig. 8O) located medially, which flattens dorsally to form the floor of the posttemporal fenestra (ptf) laterally and sutures with the supraoccipital dorsally. The posttemporal fenestra appears elliptical in posterior view, with the long axis oriented horizontally (Fig. 8O). Whereas the suture with the exoccipital appears oblique, the suture with the supraoccipital is horizontal in posterior view. The ventromedial part of the opisthotic forms a tuber-like subvertical ventromedial process (ovmp, Fig. 8O) that curves slightly posteroventrally to form the anterior wall of the jugular foramen and the posterior border of the fenestra ovalis. This gentle curvature of the process excludes the basioccipital from the jugular foramen in DMMM-PK-16-1 (Fig. 2L). The posterior aspect of the opisthotic in DMMM-PK-16-1 bears two divergent crests (opc, Fig. 8O) that flank a shallow horizontal depression (od, Fig. 8O). The lower crest is shaped like a long rod that projects laterally in the oblique direction to suture with the squamosal and quadrate. This crest terminates laterally forming the knob-like ‘tympanic process’ of Cox (1959), see tmp (Fig. 8O, P). In contrast, the upper crest is short, broader and horizontal., Published as part of Macungo, Zanildo, Benoit, Julien, Fernandez, Vincent & Araújo, Ricardo M N, 2023, X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny, pp. 1-46 in Zoological Journal of the Linnean Society 198 (1) on pages 20-24, DOI: 10.1093/zoolinnean/zlac033, http://zenodo.org/record/7922143, {"references":["Broom R. 1903. On the classification of the theriodonts and their allies. Report of the South African Association for the AdVancement of Science 1: 286 - 294.","Angielczyk KD, Benoit J, Rubidge BS. 2019. A new tusked cistecephalid dicynodont (Therapsida, Anomodontia) from the Upper Permian Upper Madumabisa Mudstone Formation, Luangwa Basin, Zambia. Papers in Palaeontology 7: 405 - 446.","Cluver MA. 1974 a. The skull and mandible of a new cistecephalid dicyndont. Annals of the South African Museum 64: 137 - 155.","Cox CB. 1972. A new digging dicynodont from the Upper Permian of Tanzania. In: Josey KA, Kemp TS, eds. Studies in Vertebrate eVolution. Edinburgh: Oliver and Boyd, 73 - 189.","Keyser AW. 1973. A preliminary study of the type area of the Cistecephalus Zone of the Beaufort Series, and a revision of the anomodont family Cistecephalidae. Geological SurVey of South Africa 62: 1 - 71.","Kammerer CF, Bandyopadhyay S, Ray S. 2016. A new taxon of cistecephalid dicynodont from the Upper Permian Kundaram Formation of India. Papers in Palaeontology 2: 569 - 584.","Olson EC. 1944. The origin of mammals based upon the cranial morphology of the therapsid suborders. Geological Society of America Special Papers No. 55. Boulder: The Geological Society of America.","Cluver MA. 1971. The cranial morphology of the dicynodont genus Lystrosaurus. Annals of the South African Museum 56: 155 - 274.","Araujo R, Fernandez V, Polcyn MJ, Frobisch J, Martins RMS. 2017. Aspects of gorgonopsian paleobiology and evolution: insights from the basicranium, occiput, osseous labyrinth, vasculature, and neuroanatomy. PeerJ 5: e 3119.","Cox CB. 1959. On the anatomy of a new dicynodont genus with evidence of the position of the tympanum. Procedings of the Zoological Society of London 132: 321 - 367.","Laass M, Schillinger B. 2015. Reconstructing the auditory apparatus of therapsids by means of neutron tomography. Physics Procedia 69: 628 - 635.","Laass M, Kaestner A. 2017. Evidence for convergent evolution of a neocortex-like structure in a Late Permian therapsid. Journal of Morphology 278: 1033 - 1057."]}

We study asset liquidity in a search-theoretic framework where divisible assets can facilitate exchange for an indivisible consumption good. The distinctive characteristics of our theory are that the asset dividend can be either positive or negative and buyers can choose whether or not to carry the asset and trade for the indivisible good. Buyers’ participation determines the demand for asset liquidity. Thus, the asset price carries a liquidity premium component which reflects the function of the asset in facilitating trade. The economy features multiple equilibria when the asset dividend is negative, due to the trade-off between the probability of trade and the endogenous cost of holding assets.

This essay surveys the literature on directed search and competitive search equilibrium, covering theory and a variety of applications. These models share features with traditional search theory, but also differ in important ways. They share features with general equilibrium theory, but with explicit frictions. Equilibria are often efficient, mainly because markets price goods plus the time required to get them. The approach is tractable and arguably realistic. Results are presented for finite and continuum economies. Private information and sorting with heterogeneity are analyzed. While emphasizing issues and applications, we also provide several hard-to-find technical results. (JEL D50, D83)