Gordonia Newton, 1893

George, Hady, Kammerer, Christian F., Foffa, Davide, Clark, Neil D. L. & Brusate, Stephen L., 2025, Micro-CT data reveal new information on the craniomandibular and neuroanatomy of the dicynodont Gordonia (Terapsida: Anomodontia) from the late Permian of Scotland, Zoological Journal of the Linnean Society 203 (3) : -

Gordonia Newton, 1893

Diagnosis: As for the type species.

Type species: Gordonia traquairi Newton, 1893

Gordonia traquairi Newton 1893:436 .

Gordonia huoleyana Newton 1893:445 .

Gordonia duffiana Newton 1893:450 .

Gordonia juddiana Newton 1893:462 .

Dicynodon traquairi von Huene 1940:280 .

Dicynodon duffianus von Huene 1940:280 .

Dicynodon huoleyanus von Huene 1940:280 .

Dicynodon juddianus von Huene 1940:280 .

Type locality: Cuties Hillock Quarry, Elgin, Scotland.

Horizon : Cuties Hillock Formation [probable equivalent of the Changhsingian Daptocephalus Assemblage Zone of South Africa ( Rubidge 1995, Viglieti et al. 2016)].

Holotype: BGS GSE 4805 [incorrectly listed as BGS GSE 11703 by King (1988) and subsequent sources: Benton and Spencer 1995, Cruickshank et al. 2005, Szczygielski and Sulej 2023; Kammerer et al. 2011].

Referred material: From the type locality: BGS GSE 11703, BGS GSE 11704 ( holotype of G. huoleyana ), ELGNM 1890.3 ( holotype of G. juddiana ), ELGNM 1978.550 [specimen labelled ‘ Gordonia Traquairi ?’ by Newton (1893); previously incorrectly reported as a specimen of the pareisaur Elginia mirabilis by Benton and Spencer (1995) and Cruickshank et al. (2005)], ELGNM 1978.559.1a,b ( holotype of G. duffiana ); from the Hopeman Sandstone Formation deposits of the Clashach quarry, Hopeman, Elgin, Morayshire (National Grid Reference NJ 163702): ELGNM 1999.5.1, ELGNM 1999.5.2, ELGNM 1999.22.

Emended diagnosis: A small (basal skull length approximately 16 cm) dicynodontoid characterized by the following combination of character states (+ indicates an autapomorphy, * indicates a newly recognized diagnostic character state based on µCT data described herein): + an anterodorsally angled lateral dentary shelf with a rod-like morphology (dorsal and lateral extensions of the shelf are roughly equal in size) that does not expand into a rounded anterior boss nor a diffuse muscle scar, does not have a transverse ridge on its dorsal surface, and does not have a fossa present near its posterior end; long, narrow intertemporal bar with narrow exposure of parietals; vertical orientation of the postorbitals in the intertemporal bar forming sagital crest; short snout (with anteroposteriorly short premaxillary region); proportionally large orbits *; dorsoventrally thin suborbital zygoma *; hooked snout tip *; narrow snout in palatal view, probably resulting from mediolaterally narrow maxilla and premaxilla *; median pterygoid plate anteroposteriorly elongate and mediolaterally narrow in palatal view *; anterior pterygoid close to sagital plane *, and short, steep mandibular symphysis.

Description

Te new 3D reconstructions of the cranium and mandible of ELGNM 1999.5.1 ( Fig. 2) generally accord with those made by Clark et al. (2004). However, we were able to more completely reconstruct the palate of this specimen, as well as for the first time provide information on its endocranial anatomy. Troughout the following description, comparisons are made to casts of the other G. traquairi specimens (e.g. NHMUK PV R 2106 ), listed in the Supporting Information, Table S1 with accompanying photographs .

Cranium As in all dicynodonts, the premaxilla of ELGNM 1999.5.1 forms the beak at the anterior end of the cranium, which would probably have been covered in a rhamphotheca in life (Jasinoski and Chinsamy-Turan 2012, Benoit et al. 2018) ( Fig. 3). Te premaxillary region (the bone anterior to the external nares) is anteroposteriorly short in lateral view. Te snout of ELGNM 1999.5.1 is neither deflected nor dorsoventrally elongate, unlike that of Lystrosaurus . In lateral view ( Fig. 3A), the premaxilla has a prominent ‘hooked’ tip, as can also be observed in NHMUK PV R 2106 ( G. traquairi holotype). Tis condition in these Gordonia specimens approaches that of Dinanomodon gilli Broom, 1932 , a taxon in which the hooked premaxillary trip is particularly exaggerated ( Kammerer et al. 2011). Tis morphology cannot be observed in other G. traquairi specimens, and it is unclear whether this is reflective of biological or taphonomic variation. Te external nares of ELGNM 1999.5.1 are anteroposteriorly longer than they are dorsoventrally tall ( Fig. 3A, C), which is also the case in ELGNM 1893.6 (" G. juddiana "). NHMUK PV R 2106 ( G. traquairi holotype) and NHMUK PV R 2109 (" G. huoleyana ") instead have external nares that are dorsoventrally taller than they are anteroposteriorly long.

Most of the palate of ELGNM 1999.5.1 can be visualized, providing substantially more information on this part of the skull than in any other known Gordonia specimen ( Fig. 4). Te anterior tip of the snout is rounded in ventral view. Te anterior palatal ridges of the secondary palate can tentatively be identified as proportionally small compared to most other dicynodontoids, but appear to be present, unlike in Kunpania scopulusa ( Angielczyk et al. 2021) . It is unclear whether the proportionally small size of the anterior palatal ridges is a true biological character or a result of taphonomic factors. A median palatal ridge can be identified along the posterior end of the palatal surface of ELGNM 1999.5.1 ( Fig. 4) and is confluent with the vomer. Tere are no longitudinal depressions along the secondary palate ( Fig. 4).

Te lateral surfaces of the caniniform processes of ELGNM 1999.5.1 are convex laterally and do not have any clear depressions or protrusions ( Fig. 3). Tey are interpreted as being formed by the maxillae, as is the case in all other dicynodonts. Te caniniform processes of NHMUK PV R 2106 ( G. traquairi holotype), NHMUK PV R 2109 (" G. huoleyana "), and ELGNM 1893.6 (" G. juddiana ") also have this morphology. Unlike the maxillae of closely related taxa, this region in ELGNM 1999.5.1 seems to be proportionally mediolaterally narrow ( Kammerer et al. 2011). A similar morphology is observed in Jimusaria sinkianensis , but in most other dicynodontoids this region is widened, with a greater degree of ‘splay’ of the caniniforms ( Kammerer et al. 2011). As in most dicynodontoids, the only dentition present in G. traquairi is the caniniforms, which erupt from the maxillae ( Kammerer et al. 2011). Te caniniforms of ELGNM 1999.5.1 are directed ventrally, like those of the other G. traquairi specimens in which they are preserved [ NHMUK PV R 2106 ( G. traquairi holotype), ELGNM 1893.6 (" G. juddiana "), NHMUK PV R 2109 (" G. huoleyana "), and NHMUK PV R 2107 (referred to G. traquairi )].

A nasal boss is present in ELGNM 1999.5.1, and is best seen in lateral view ( Fig. 3A, C). It is a single, slightly raised expansion of the nasals, which is continuous between both bones, like that of other Permian dicynodontoids. A boss is also present in NHMUK PV R 2106 ( G. traquairi holotype). A nasal boss cannot be clearly identified in NHMUK PV R 2109 (" G. huoleyana "), ELGNM 1893.6 (" G. juddiana "), or NHMUK PV R 2107 (referred to G. traquairi ), but this more likely represents taphonomic artefact than biological variation.

Tere is a slight circumorbital rim extending across the orbital margins of what is probably the prefrontal through the postorbital in ELGNM 1999.5.1 ( Kammerer et al. 2011) ( Fig. 3D, E). A similar circumorbital rim is present in NHMUK PV R 2106 ( G. traquairi holotype) but is not as well developed in other specimens. A weakly-developed rim is visible at the anterodorsal corner of the orbit (probably corresponding to the prefrontal margin) of NHMUK PV R 2109 (" G. huoleyana ") and ELGNM 1893.6 (" G. juddiana "), but it does not appear to continue posteriorly. Kammerer et al. (2011) noted that G. traquairi has relatively large orbits compared to other dicynodonts, and this is supported by the new data presented herein ( Fig. 3).

In dorsal view, the postorbitals converge posterior to the pineal foramen, which is located near the anterior end of the intertemporal bar ( Fig. 3D–F). An interorbital depression can be identified anterior to the pineal foramen, which probably corresponds to the region occupied by the preparietal. Te pineal foramen is anteroposteriorly longer than it is mediolaterally wide and it is similar in shape to that of ELGNM 1893.6 (" G. juddiana "). NHMUK PV R 2109 (" G. huoleyana ") also has a preserved pineal foramen, but it is proportionally larger than that of ELGNM 1999.5.1. Te pineal foramen of " G. duffiana " ( ELGNM 1978.559.1) is less elongated than that of ELGNM 1999.5.1 and shows greater exposure in the intertemporal bar, not being overlapped by the postorbitals ( Newton 1893). Te adductor fossa of the right postorbital of ELGNM 1999.5.1 is medial to the posterior margin of the right orbit. Much of the postorbitals are dorsal to the rest of the skull roof as they form the lateral surfaces of the sagital crest ( Fig. 5). As noted by Kammerer et al. (2011), the sagital crest of NHMUK PV R 2106 ( G. traquairi holotype) is proportionally large (unusually so for a dicynodont of its size), mediolaterally narrow (providing only slight dorsal exposure of the parietals), and formed by vertically oriented postorbitals, and this mostly matches what is seen in the new data presented herein. Te intertemporal portion of the postorbitals shows more horizontal orientation in ELGNM 1999.5.1 than in the holotype, particularly anteriorly, although the postorbital surface is near-vertical at the apex of the crest. In dorsal view, the crest can be seen to be thinnest at its mediodorsal edge and expands in length lateroventrally ( Fig. 5). Te crest is also laterally thicker anteriorly than posteriorly. In lateral view, the sagital crest increases in height posteriorly from the pineal foramen, before decreasing in height at the posterior end of the skull. Similar to ELGNM 1999.5.1, the crest of NHMUK PV R 2106 ( G. traquairi holotype) gradually increases in dorsoventral height posteriorly from the anterior origin of the crest and maintains a similar height for the majority of the crest until it decreases in height at its posterior end. Te crest of NHMUK PV R 2109 (" G. huoleyana ") is not as tall as that of ELGNM 1999.5.1 and NHMUK PV R 2106 ( G. traquairi holotype) but has similar changes in dorsoventral height throughout the crest to those of the other two specimens. Te crests of NHMUK PV R 2107 (referred to G. traquairi ) and ELGNM 1893.6 (" G. juddiana ") are considerably less tall than those of the previously mentioned G. traquairi specimens and are instead the same height as the rest of the dorsal surface of the skull roof. Such variation in crest shape between specimens, where smaller, skeletally immature specimens have smaller crests, lines up with known trends in therapsid ontogeny ( Jasinoski et al 2015, Kammerer et al. 2015, Jasinoski and Abdala 2016). Tis suggests a biological reason behind the variation between specimens that is related to muscle area. Te postorbitals of ELGNM 1999.5.1 articulate with the parietals medially, which extend ventrally beyond the crest. Te mediolaterally thin crest indicates that the dorsal exposure of the parietals was narrow.

Unlike for most of the specimen, there is a clearly identifiable suture between the lef jugal and the zygomatic arch of the lef squamosal ( Fig. 6A). Te jugal–squamosal suture forms a diagonal line immediately posterior to the lef orbit in lef lateral view, such as is seen in many other Permian dicynodontoids, e.g. Dicynodon lacerticeps ( Kammerer et al. 2011) . Te other cranial specimens of G. traquairi also preserve the zygomatic arch, but precise jugal morphology is difficult to determine. Te suborbital portion of the zygoma is remarkably dorsoventrally thin in ELGNM 1999.5.1 ( Fig. 6), unlike the thicker structures in many other dicynodontoids [e.g. NHMUK PV OR 47047 ( Daptocephalus leoniceps )], but similar to that of Delectosaurus arefevi Kurkin, 2001 ( PIN 4644/1) (Kammerer, pers. observ.). Comparable zygomatic proportions are present in NHMUK PV R 2106 ( G. traquairi holotype), NHMUK PV R 2109 (" G. huoleyana "), and ELGNM 1893.6 (" G. juddiana "), suggesting that this is a consistent feature in Gordonia .

Only the lef squamosal is completely preserved in ELGNM 1999.5.1 ( Fig. 6), while the right is split between this specimen and ELGNM 1999.5.2 ( Clark et al. 2004). In dorsal view, the width of the lef zygomatic arch expands towards its posterior end. In dorsal view, the posterior end of the squamosal is concave, and the medial portion of the lef squamosal articulates with the bones of the sagital crest. Near the anterior end of the zygomatic arch, there is an abrupt shif in morphology of the zygomatic arch as it is dorsoventrally taller than it is mediolaterally wide anteriorly and then becomes mediolaterally wide posteriorly for much of its anteroposterior length. Tis morphology is not seen in NHMUK PV R 2106 ( G. traquairi holotype), NHMUK PV R 2109 (" G. huoleyana "), NHMUK PV R 2107 (referred to G. traquairi ), and ELGNM 1893.6 (" G. juddiana "), indicating that this shif in morphology in ELGNM 1999.5.1 represents taphonomic artefact rather than biological variation. All the G. traquairi specimens with well-preserved lef squamosals have squamosal ventral processes that are exposed posteriorly. In lef lateral view, the anteroposterior length of the quadrate ramus of the squamosal of ELGNM 1999.5.1 is greatest dorsally, and gradually decreases ventrally ( Fig. 6A). Te adductor fossa of the lef squamosal can be identified in lef lateral and posterior views as the fossa between the quadrate and zygomatic rami ( Fig. 6B).

Te lef quadrate of ELGNM 1999.5.1 is preserved with litle distortion. In palatal view, the roughly equal-sized medial and lateral condyles of the quadrate can be identified with a trochlea between them, which would have articulated with the mandible ( Fig. 4). Te right quadrate contacts the right quadrate ramus of the pterygoid, but the lef quadrate only nearly contacts the lef quadrate ramus of the pterygoid. Tis asymmetrical difference is probably a result of inconsistent preservation and not biological variation, and in life, there would have been contact on both sides. NHMUK PV R 2106 ( G. traquairi holotype) and ELGNM 1893.6 (" G. juddiana ") show comparable quadrate morphology. Only the lef quadratojugal of ELGNM 1999.5.1 can be confidently identified. Te bone is a thin, broad plate that is flush with the squamosal. In posterior view, the ventral process of the squamosal occludes the quadratojugal. Similarly, NHMUK PV R 2106 ( G. traquairi holotype) and NHMUK PV R 2107 (referred to G. traquairi ) also possess lef quadratojugals that are visible in lef lateral view, which are continuous with the squamosals. In NHMUK PV R 2109 (" G. huoleyana ") and ELGNM 1893.6 (" G. juddiana "), the quadratojugals appear to be missing, exposing the shallow articular fossa where they would have overlapped the anteroventral face of the squamosal. Te lef quadratojugal foramen of ELGNM 1999.5.1 is dorsoventrally taller than it is mediolaterally wide ( Fig. 6A).

Part of the vomer of ELGNM 1999.5.1 can be identified as a thin ridge between the internal nares, confluent anteriorly with the median palatal ridge of the premaxilla, and has a ventral margin offset from the rest of the palate ( Fig. 4). Te ridge has a consistent mediolateral width throughout (narrow and blade-like), which is unlike that of other dicynodontoids such as D. lacerticeps where a large portion of the anterior part of the vomer ridge is mediolaterally wider than the rest of the ridge ( Kammerer et al. 2011). Posteriorly, the vomer splits at an acute angle, bounding an isosceles triangular fossa anterior to the interpterygoid vacuity. Lateral and dorsal to this split, horizontally oriented laminar portions of the ventral surface of the vomer form part of the primary palate. Te dorsal portion of the vomer was incompletely visible in the CT data; what could be reconstructed is a tall, blade-like median element partially dividing the nasal capsule, similar to that known in other dicynodontoids (e.g. Lystrosaurus ; Cluver 1971).

Te palatine bones of ELGNM 1999.5.1 border the internal nares laterally ( Fig. 4). Te exact morphology of the palatines is unclear, due to poor resolution at the edges of the internal narial cavities. Te right internal narial opening in particular appears damaged, with an opening extending much further anterior (beyond the caniniform process; Fig. 4A) than in other dicynodonts. Te posterior halves of the internal nares are beter preserved and are almost parallel to each other, unlike those of D. lacerticeps , which show greater transverse expansion posteriorly ( Kammerer et al. 2011). Te right palatine of ELGNM 1999.5.1 has a dorsal projection ( Fig. 7A, B), which is angled anterolaterally and has a concave medial face. Tis portion of the palatine appears to bound part of the labial fossa. It is similar in morphology to that of other dicynodontoids, but is mediolaterally wider and more strongly dorsally angled than that of earlier diverging taxa, such as Niassodon mfumukasi ( Castanhinha et al. 2013) .

Much of the following anatomy of the pterygoid of ELGNM 1999.5.1 described herein helps distinguish G. traquairi from other taxa and cannot be seen in the reconstructions made by Clark et al. (2004) .

In palatal view, the pterygoid of ELGNM 1999.5.1 is X-shaped with two anterior rami diverging slightly anterolaterally and two quadrate rami diverging more widely posterolaterally from the medial plate ( Fig. 4). Te anterior rami of ELGNM 1999.5.1 diverge much less laterally than those of other taxa, such as Dicynodon spp. ( Kammerer et al. 2011, Kammerer 2019). Tis morphology contributes to the relatively narrow palate of ELGNM 1999.5.1 compared to other Permian dicynodontoids (see above) ( Kammerer et al. 2011, Kammerer 2019, Liu 2021), and is instead more similar to some non-dicynodontoid dicynodont taxa such as Compsodon helmoedi van Hoepen, 1934 ( Angielczyk and Kammerer 2017). Tere are keels on the anterior rami of ELGNM 1999.5.1, which are best visible in lef lateral view ( Fig. 7A). Similar keels are present throughout Dicynodontoidea, other than in kannemeyeriiforms ( Kammerer et al. 2011). Te keels of ELGNM 1999.5.1 gradually increase in dorsoventral height towards their anterior ends. In palatal view, there is a distinct indentation anterior to the lef anterior ramus of the pterygoid, which is best interpreted as the lateral palatal fenestra based on its position and its somewhat teardrop-shaped outline ( Fig. 4B). Te palatal fenestrae of other dicynodontoids, such as D. lacerticeps , have a similar shape ( Kammerer et al. 2011). Te interpterygoid vacuity can be identified anterior to the median pterygoid plate and is also roughly teardrop-shaped, but anteroposteriorly elongate ( Fig. 4A). A labial fossa appears to be present lateral to the lef anterior pterygoid ramus ( Fig. 7B). Te elements bounding this fossa cannot be determined; by comparison to other dicynodontoids they probably consist of the maxilla, jugal, and palatine ( Kammerer et al. 2011). It is unlikely that the pterygoid ramus directly contacts the fossa.

Te medial pterygoid plate of ELGNM 1999.5.1 is substantially anteroposteriorly longer than it is mediolaterally wide ( Fig. 4). Te median plate is proportionally anteroposteriorly longer and mediolaterally narrower than in most other Permian dicynodontoids, such as NHMUK PV OR 47047 ( Daptocephalus leoniceps ), NHMUK PV R 4039 ( V. trautscholdi), and Dicynodon spp. and Turfanodon spp. ( Kammerer et al. 2011, Kammerer 2019, Liu 2021) ( Fig. 4), but is comparable to that of Jimusaria spp. (see IVPP V 341407 in: Kammerer et al. 2011, Shi and Liu 2023). Tere are keels on the lateral sides of the medial plate that are continuous with the keels of the anterior rami ( Fig. 7A). Te crista oesophagea can be identified as a weak ridge posterior to the interpterygoid vacuity. Te crista oesophagea is present in most dicynodontoids except for Daptocephalus spp. ( Kammerer 2019). It should be noted that juvenile specimens of Dicynodon lacerticeps also lack a crista oesophagea, indicating potential ontogenetic control on this feature in other taxa ( Kammerer 2019).

Te quadrate rami of the pterygoid of ELGNM 1999.5.1 diverge posterolaterally to articulate with the quadrates ( Fig. 4). Both quadrate rami extend slightly ventrally from the medial plate ( Fig. 7A) like those of NHMUK PV R 2106 ( G. traquairi holotype), but unlike ELGNM 1893.6 (" G. juddiana ") and NHMUK PV R 2109 (" G. huoleyana ") in which the quadrate rami extend ventrally at a steeper angle, possibly due to distortion. Te ventral sides of the quadrate rami are continuous with the keels on the lateral sides of the medial plate. In lateral views, the height of the quadrate rami is comparable to that of the lateral sides of the medial plate.

Te parasphenoid of ELGNM 1999.5.1 is a thin, elongate element flush with other internal cranial bones ( Fig. 8A, B) and probably fused with the basisphenoid, as in other dicynodonts ( Macungo et al. 2022). A small, median ridge on the dorsal surface of the parasphenoid can be tentatively identified as part of the base of the cultriform process. A parasphenoidal sulcus is present on the dorsal surface as a shallow depression anterior to the endocranial cavity. In palatal view, a single foramen for the internal carotid artery is visible, presumably borne on the basisphenoid ( Fig. 4). It is slightly offset from the sagital plane, indicative of it being one of a pair of foramina (the other not preserving). It is in a similar position as the same structure in Lystrosaurus , based on UMZC T 758 and UMZC T 788 and what is described by Cluver (1971). For the basisphenoid, two additional notable features can be identified. Te first is a dorsally projecting tab-like structure that is angled slightly posteriorly, which is best interpreted as the clinoid process ( Fig. 8A). Te second is that the basal tubera (also formed by the basioccipital posteriorly) are nearly vertical, with no clear ridges along their long axes ( Fig. 4). Te tubera form the posterior portion of the stapedial facet, which is open distally. Most details of the sphenoid elements (especially those that cannot be identified in palatal view) could not be observed in the reconstructions by Clark et al. (2004).

Te prootic dorsal processes compose the dorsally extending portion of the internal cranial bones that articulate with the occiput ( Fig. 9B, C). Te pila antotica is visible as a weakly-developed, anteriorly-directed process at the anteroventral margin of the prootic (identity of this element as prootic based on comparison with other synapsids; it is likely that the prootic is fused with other elements to form a periotic as in other dicynodonts; see below). Te pila antotica is unusually low, which probably represents incomplete preservation or visualization. Te only other specimens of G. traquairi with identifiable prootic regions are NHMUK PV R 2106 ( G. traquairi holotype), NHMUK PV R 2109 (" G. huoleyana "), and NHMUK PV R 2107 (referred to G. traquairi ). However, these specimens do not reveal much detail concerning these elements, and do not substantially aid in determining pila antotica morphology in Gordonia . Te opisthotics of ELGNM 1999.5.1 are inferred to contribute to the borders of the vestibules, and their paroccipital processes are identifiable in posterior view as being flush with the rest of the occiput ( Fig. 9A). A similar paroccipital process can also be identified in posterior view of the occiput of ELGNM 1893.6 (" G. juddiana ").

Te prootics and opisthotics also contain the vestibule (described in the description of the endocast and vestibule below). Te opening for the vestibule to meet the endocranial cavity can be seen in lef medial view of the basicranium, and based on the morphology known for other dicynodont braincases ( Macungo et al. 2022), would have been enclosed by the prootic, opisthotic, and basioccipital ( Fig. 8D). Te jugular foramen and opening for the vestibule can also be seen in lef medial view of the basicranium and have a very similar position to what is seen throughout dicynodonts (e.g. Lystrosaurus ; UMZC T 758 and UMZC T 788) ( Surkov and Benton 2004). Te basioccipital median ridge is dorsally elevated ( Fig. 8A–C). Additionally, the foramen for the cranial nerve VII (facial nerve), the fenestra basicranialis, and the foramen ovale can also be identified ( Fig. 8D). Tese neurocranial elements of ELGNM 1999.5.1 could not be identified in the models made by Clark et al. (2004), emphasizing the value of novel tomographic study of this specimen.

Te occiput is presumed to be composed of a periotic, which is a fusion of several elements (minimally the prootic and opisthotic, but ofen incorporating several additional elements, e.g. supraoccipital, exoccipitals, and basioccipital), as in most other dicynodonts ( Kammerer et al. 2011, Kammerer 2019). An incompletely preserved occipital condyle (which would be formed by paired, lateral exoccipital and median, ventral basioccipital elements) is present ventral to the foramen magnum of ELGNM 1999.5.1 ( Fig. 9A). Te foramen magnum is oval-shaped, with its dorsoventral height greater than its mediolateral width, as in ELGNM 1893.6 (‘ G. juddiana ’), and as is common in dicynodonts (Laass and Kaestner 2017). Tere is no clear floccular fossa present on the medial side of the supraoccipitals, but this may be a result of taphonomic factors. Tere is evidence for an ‘unossified zone’, a feature also seen throughout non-dicynodontoid dicynodonts ( Laass 2015, Laass et al. 2017, Simão-Oliveira et al. 2019). Te ‘unossified zone’ is most visible in the endocast described below.

Te laminar portion of the fused mesethmoid and orbitosphenoid (anterior plate) of ELGNM 1999.5.1 is flush with the skull roof ( Fig. 7C–F). Additionally, part of the olfactory cavity can be identified. Most notably, the mesethmoid posterior wall can be observed. In anterior and posterior views, this wall is simple and thin, but in lateral views, the wall is a ventrally directed and dorsoventrally taller than the anteroposteriorly long, triangular plate pointing anteroventrally. Considering that much of the ethmoid region and olfactory cavity is not well preserved, this pointed portion of the anterior plate may also not be complete, and it is possible that it formed a more extensive median structure separating the orbits, as in many other dicynodonts ( King 1988).

Mandible Te mandible of ELGNM 1999.5.1 is completely preserved and is not taphonomically distorted in any way that obscures much of its anatomical details from being discerned .

Te dentaries of ELGNM 1999.5.1 have a typical dicynodontoid morphology [as is described by Kammerer (2019)]. Anteriorly, the dentaries fuse and largely contribute to the mandibular symphysis, with a pointed beak at its anterodorsal tip ( Fig. 10). Te symphysis is rectangular (dorsoventrally taller than mediolaterally wide), and dorsoventrally shorter than that of other other Permian dicynodontoids, including Dicynodon angielczyki and Jimusaria monanensis

16 • George et al.

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( Kammerer 2019, Shi and Liu 2023). Te anterior surface of the symphysis of ELGNM 1999.5.1 is also more steeply angled than that of D. angielczyki and J. monanensis ( Kammerer 2019, Shi and Liu 2023). Additionally, there are two ridges diverging ventrolaterally from each other at about the midpoint of the anterior surface of the symphysis. Tey represent the ventral parts of the dentaries, and the indented part of the anterior surface of the symphysis ventral to these ridges represents the splenial. Te dorsal portion of the symphysis is bifurcated into two dorsally projecting protrusions with a notch between them, which is a preservational artefact associated with incomplete preservation or scan resolution (particularly evident in posterior view; Fig. 10D), in which the lef side of the dentary tip is missing. A posterior dentary sulcus can be identified on the dorsal surface of each mandibular ramus immediately posterior to the flat dentary tables, situated posterolateral to the posterior dorsal surface of the mandibular symphysis. Tese sulci are narrow and deep, run along the dorsal surface of the mandible, and extend approximately across the anterior third of the rami. Te lateral edges of the symphysis are swollen. Unlike ELGNM 1999.5.1, NHMUK PV R 2106 ( G. traquairi holotype) appears to have a rounded anterior face of the mandibular symphysis in lateral view. However, this is probably artefactual; the dorsal surface of this region in casts is strongly indented, unlike any other dicynodonts and indicative of incomplete preservation in this region.

In lateral view of ELGNM 1999.5.1, the anterior ends of the dentaries are dorsoventrally taller than any other part of the bones ( Fig. 10). Te lateral dentary shelf of each mandibular ramus is well exposed in lateral views. Te lateral dentary shelves are angled anterodorsally, have a rod-like morphology (with the dorsal and lateral extensions of the shelf being roughly equal in size), and do not expand into a rounded anterior boss nor a diffuse muscle scar ( Fig. 10). Instead, the anterior portion of each dentary shelf is slightly swollen. A similar lateral dentary shelf can be seen in NHMUK PV R 2106 ( G. traquairi holotype). Te combination of these characteristics is unique to G. traquairi among dicynodonts [as is noted by Kammerer et al. (2011)]. Te lateral dentary shelf of Jimusaria monanensis is similar, but not as strongly angled anterodorsally ( Shi and Liu 2023). Te non-dicynodontoid dicynodont Compsodon helmoedi also has an anterodorsally angled dentary shelf but, unlike in G. traquairi , it is much more prominent, with a transverse ridge on the dorsal surface of the dentary shelf and a fossa present near the posterior end of the dentary shelf in that taxon ( Angielczyk et al. 2023). Te lateral dentary shelves largely contribute to the dorsal margin of the mandibular fenestrae, which are considerably anteroposteriorly longer than they are dorsoventrally tall ( Fig. 10). Tis mandibular fenestra shape is also present in NHMUK PV R 2106 ( G. traquairi holotype) and NHMUK PV R 2019 (" G. huoleyana "). Te suture between the dentary and lef angular of ELGNM 1999.5.1 cannot be identified, but is probably represented in NHMUK PV R 2106 ( G. traquairi holotype) by a sinusoidal line running dorsoventrally at the posterior end of the mandibular fenestra. Te sinusoidal line then connects with the posterior end of the mandibular fenestra.

Te reflected laminae of the angulars are ventrally directed projections posterior to the mandibular fenestrae, and each is bisected by a central groove. A similar reflected lamina morphology can be seen in many other Permian dicynodontoids ( Kammerer et al. 2011, Kammerer 2019, Olroyd and Sidor 2022). Te posterior ends of the surangulars are slightly laterally flared, and this characteristic can also be seen in NHMUK PV R 2106 ( G. traquairi holotype) and NHMUK PV R 2109 (" G. huoleyana "). Tere is a wide separation between the articulars and the reflected lamina, a trait seen throughout Permian dicynodontoids ( Olroyd and Sidor 2022). Te medial and lateral condyles of the articulars can be identified on either side of the median ridge, which would have articulated with the quadrate. Retroarticular processes protrude ventrally from the posterior ends of the articulars.

Endocast and vestibule Most of the endocast and the lef vestibule of ELGNM 1999.5.1 were reconstructed ( Fig. 11), except for the olfactory bulbs, most of the olfactory tract, the entirety of the right vestibule, all semicircular canals, and associated bony canals enclosing blood vessels and nerves. Generally, the endocast is not drastically distorted in any way that obscures identification of much of its anatomy. In the description herein, the endocast of ELGNM 1999.5.1 is referred to as the endocast of G. traquairi , being the only endocast of this taxon known in any detail. As illustrated by Newton (1893: pl. 32, fig. 1), part of the dorsal surface of the brain endocast appears exposed in ‘ G. duffiana ’ ( ELGNM 1978.559.1), but this comprises only a small portion directly underlying the skull roof between the orbits and pineal foramen.

In the lateral view of the endocast ( Fig. 11E), the forebrain can be identified as a beam-shaped structure showing a ‘keel’ on its ventral side. Tis keel is a result of mediolateral compression of the parietals in this specimen, and is unlikely to have been a feature of the anterior braincase in the living animal (in which the floor was probably unossified).Te forebrain is anteroposteriorly longer than it is dorsoventrally tall, and mediolaterally thin in dorsal view. Tis morphology can be atributed to a combination of the legitimately narrow intertemporal region in the skull as well as taphonomic distortion due to compression. Te preserved portion of the olfactory tract is within the olfactory cavity in the orbitosphenoid–mesethmoid element. Overall, the elongated shape of the forebrain of G. traquairi resembles that of various earlier-diverging dicynodonts, such as Niassodon mfumukasi , Pristerodon mackayi , Rastodon procurvidens , and Diictodon feliceps Owen, 1876 , as well as the dicynodontoid Lystrosaurus ( Edinger 1955, Hopson 1979), rather than the bulbous and proportionally large forebrains of the cistecephalid emydopoids Kawingasaurus fossilis and Kembawacela spp. ( Castanhinha et al. 2013, Laass 2015, Laass and Kaestner 2017, Laass et al. 2017, Angielczyk et al. 2019, Simão-Oliveira et al. 2019, Araújo et al. 2022). Tere is no bisected swelling in the forebrain of G. traquairi , again similar to N. mfumukasi , P. mackayi , R. procurvidens , D. feliceps , and Lystrosaurus , and unlike K. fossilis and Kembawacela spp. ( Edinger 1955, Castanhinha et al. 2013, Laass 2015, Laass and Kaestner 2017, Laass et al. 2017, Angielczyk et al. 2019, Simão-Oliveira et al. 2019, Araújo et al. 2022). Te most distinguishing characteristic of the endocast of G. traquairi is the well-developed pineal body ( Fig. 11E). In lateral view, the pineal body protrudes anterodorsally within the mediolaterally thin sagital crest, and has an anteriorly directed projection at its dorsal end, giving it a triangular shape. Te anterior side of the triangular dorsal end is exposed to the outside of the skull through the pineal foramen immediately anterior to the sagital crest. Tis morphology is unlikely to be a preservational artefact, but instead largely reflective of the true endocast morphology, as the element is entirely enclosed by preserved skeletal elements that are not drastically taphonomically altered. Te anterior direction of the pineal body can be atributed to the presence of the tall, narrow sagital crest; the same structure in Lystrosaurus (where no sagital crest is present) is a simple, vertical tube ( Edinger 1955).

Te midbrain forms the ventrally directed portion of the endocast leading towards the hindbrain at the posterior end of the endocast ( Fig. 11E). Te midbrain is strongly dorsoventrally angled, creating an almost 45 º angle between the forebrain and hindbrain. Such an angle between the forebrain and hindbrain can be observed in N. mfumukasi , P.mackayi , D. feliceps , K. fossilis , and Lystrosaurus , but not in R. procurvidens (although this may be related to taphonomic dorsoventral flatening of the specimen used to generate the endocast) ( Edinger 1955, Castanhinha et al. 2013, Laass 2015, Laass and Kaestner 2017, Laass et al. 2017, Simão-Oliveira et al. 2019). Dorsal to the ventrally directed portion of the endocast, a small posteriorly directed projection can be identified as an ‘unossified zone’, a feature usually seen in dicynodont endocasts and suggested to house vascular sinuses ( Laass 2015, Laass et al. 2017, Simão-Oliveira et al. 2019). Te midbrain of G. traquairi is not as dorsoventrally elongate as that of D. feliceps (Laass et al. 2017) . Te hypophysis of G. traquairi is identifiable as a ventral extension of the posterior half of the endocast, similar to that of N.mfumukasi , P. mackayi , R. procurvidens , and D. feliceps ( Castanhinha et al. 2013, Laass 2015, Laass et al. 2017, Simão-Oliveira et al. 2019).

Te hindbrain of G. traquairi is mediolaterally wider than the forebrain and the descending portion of the midbrain ( Fig. 11E). Tis is unlike the endocasts of N.mfumukasi , P. mackayi , R. procurvidens , D. feliceps , and K. fossilis ( Castanhinha et al. 2013, Laass 2015, Laass and Kaestner 2017, Laass et al. 2017, Simão-Oliveira et al. 2019, Araújo et al. 2022). In lateral view, no clear parafloccular lobe can be observed, and there is no evidence of a parafloccular fossa (which encloses the lobe) in the supraoccipital. It is possible that Gordonia had no parafloccular fossae, which are greatly reduced in other bidentalian dicynodonts ( Angielczyk and Kurkin 2003). However, a proportionally small parafloccular lobe might not be detectable with the available data for this specimen. All other published dicynodont endocasts have parafloccular lobes protruding laterally from the hindbrain ( Castanhinha et al. 2013, Laass 2015, Laass and Kaestner 2017, Laass et al. 2017, Simão-Oliveira et al. 2019). No medulla oblongata, such as that of R. procurvidens ( Simão-Oliveira et al. 2019) , can be confidently identified in the endocast of G. traquairi . Additionally, no longitudinal medial sulcus can be identified separating the ventral surface of the hindbrain (where the pons is inferred to be), unlike that of R. procurvidens ( Simão-Oliveira et al. 2019) .

Te lef vestibule is anteroposteriorly short in lef lateral view ( Fig. 11E), unlike that of N. mfumukasi , P. mackayi , R. procurvidens , and D. feliceps , which have anteroposteriorly longer vestibules relative to total endocast size ( Castanhinha et al. 2013, Laass 2015, Laass et al. 2017, Simão-Oliveira et al. 2019). Te lef vestibule of G. traquairi is not inflated, unlike that of K. fossilis and Kembawacela spp. (Laass and Kaestner 2017, Angielczyk et al. 2019, Araújo et al. 2022). Furthermore, the vestibule of G. traquairi does not taper in anteroposterior length down its dorsoventral length, as in N. mfumukasi , P.mackayi , and R. procurvidens ( Castanhinha et al. 2013, Laass 2015, Simão-Oliveira et al. 2019). In posterior view ( Fig. 11C), the vestibule of G. traquairi is almost as mediolaterally wide as the hindbrain, which is unlike N. mufumukasi , P. mackayi , R. procurvidens , and D. feliceps , which have hindbrains that are considerably mediolaterally wider than their vestibules ( Castanhinha et al. 2013, Laass 2015, Laass et al. 2017, Simão-Oliveira et al. 2019). Te skeletal elements of G. traquairi surrounding the vestibule are not taphonomically altered to an extent that would cause such extreme mediolateral widening of the vestibule (e.g. dorsoventral flatening of the skull), and this wide morphology likely approximates the true vestibular morphology as it fills most of the prootic region.

Body mass estimates and encephalization quotient values of Gordonia

Body mass estimates ranged from 7726.81 g to 86807.11 g ( Table 1). Since the greatest value is about 3.8 times larger than the next greatest value ( 22999.57 g), and there are substantially smaller differences between the other estimates, the greatest estimate was excluded from calculation of the average body mass value ( 11882.01 g). Te endocast volume without the pineal body ( 9850.9 mm 3) is about 90% of the volume with the pineal body ( 10930.04 mm 3), and consequently, the Manger EQ value calculated without the pineal body (0.2) is about 91% of the value calculated with the pineal body (0.22).

Phylogenetic analysis results

Te only notable differences between the scorings for the ‘ Gordonia traquairi ’ OTU and ‘Te Elgin Marvel’ OTU that are not related to missing data for either OTU are continuous characters 12 (angle between ascending and zygomatic processes of the squamosal is 1.396 in the former OTU and 2.379 in the later OTU) and 13 (angulation of the occiput relative to the palate, expressed as the ratio of dorsal and basal lengths of the skull is 1.067 in the former OTU and 1.49 in the later OTU). Te phylogenetic analysis resulted in 1 most parsimonious tree ( MPT) with a length of 1370.86 steps (consistency index = 0.229, retention index = 0.708) ( Fig. 12). ‘Te Elgin Marvel’ OTU is robustly recovered as the sister-taxon to the ‘ Gordonia traquairi ’ OTU (recovered in 97 replicates, Bremer support value = 3.317), supporting the referral of ELGNM 1999.5.1 to Gordonia traquairi .

Furthermore, Gordonia is recovered within a clade also containing Jimusaria (recovered in 60 replicates, Bremer support value = 2). Synapomorphies uniting this clade are continuous Ch. 8: 0.117 –0.118 → 0.094 –0.113 (narrow median pterygoid plate relative to basal skull length), continuous Ch. 11: 9.599 – 9.663 → 9.319 (area of internal nares small relative to basal skull length), continuous Ch. 12: 9.9–10.25 → 8.9 (small angle between ascending and zygomatic process of the squamosal), continuous Ch. 13: 0.920 –0.926 → 0.944 -0.922 (strong angulation of the occiput relative to the palate), discrete Ch. 38: 1 → 0 (absence of prefrontal bosses), discrete Ch. 45: 2 → 1 (preparietal present and flush with skull roof), discrete Ch. 67: 1 → 0 (squamosal separated by tabular bone from supraoccipital), discrete Ch. 107: 1 → 0 (tabulars contact opisthotics), and discrete Ch. 172: 1 → 0 (unornamented anterior face of dentary symphysis). Within this clade, Jimusaria sinkianensis is recovered immediately outside of a subclade containing Jimusaria monanensis and Gordonia (recovered in 56 replicates, Bremer support value = 1.889). Tis result mirrors Kammerer (2019), Angielczyk et al. (2021), and Liu (2021) in recovering Gordonia as the sister-taxon to J. sinkianensis , but not Kammerer and Ordoñez (2021), Macungo et al. (2022), and Shi and Liu (2023). Instead, these studies recover J. sinkianensis ( Jimusaria spp. in the case of Shi and Liu (2023)) immediately outside of the clade containing Gordonia and ‘higher’ dicynodontoids (e.g. Kannemeyeriiformes).

Moreover, our phylogenetic analysis recovers a relatively inclusive Lystrosauridae containing Peramodon , Daptocephalus , Dinanomodon , Turfanodon , the Jimusaria + Gordonia clade, Syops , Basilodon , Sintocephalus , Euptychognathus , and Lystrosaurus [all taxa more closely related to Lystrosaurus than to Kannemeyeria or Dicynodon ; see Kammerer and Angielczyk (2009) for clade definitions], but this large Lystrosauridae clade is not strongly supported (recovered in <50 replicates, Bremer support value = 0.806). Synapomorphies uniting this version of Lystrosauridae in our analysis are continuous Ch. 3: 0.253→ 0.23–0.244 (small width of interorbital skull roof relative to basal length of skull), continuous Ch. 7: 1.468 –1.485 → 1.380 – 1.443 (dorsoventrally short anterior pterygoid keel in lateral view relative to height of non-keel ramus), discrete Ch. 98: 2 → 1 (basisphenoid contribution to the basisphenoid–basioccipital tuber slopes anterodorsally at a steeper angle such that the parabasisphenoid contribution is still somewhat ridge-like but the portion of the ridge on the anterior surface of the tuber is more vertically-oriented), discrete Ch. 142: 2 → 3 (number of sacral vertebrae is six or more), discrete Ch. 165: 1 → 0 (proximal articular surface of the femur present as a weak swelling that is mostly limited to the proximal surface of the bone).

Recovery of Gordonia and Jimusaria within Lystrosauridae is a resultnotfoundinotherrecentphylogeneticanalyses( Kammerer 2019, Angielczyk et al. 2021, Kammerer and Ordoñez 2021, Liu 2021, Macungo et al. 2022, Shi and Liu 2023), although the recovery of Jimusaria in this clade has previously been obtained by Kammerer et al. (2011). Additionally, Lystrosauridae and Kannemeyeriiformes represent sister-taxa in the recovered topology, a result previously obtained by Macungo et al. (2022), but unlike other recent topologies that found Kannemeyeriiformes to be the sister-taxon of a Gordonia + J. sinkianensis clade ( Kammerer 2019, Kammerer and Ordoñez 2021, Liu 2021), or Kannemeyeriiformes to be the sister-taxon of a clade containing Basilodon , Sintocephalus , Peramodon , Daptocephalus , Dinanomodon , and Turfanodon ( Shi and Liu 2023) .

Te stratigraphically problematic Chinese taxon Kunpania scopulusa is here recovered as the sister-taxon to all other bidentalians, rather than in the basal dicynodontoid position found by Angielczyk et al. (2021). Angielczyk et al. (2021) commented on the extremely weak support for Kunpania as a dicynodontoid, so this minor lability in its position on the tree is unsurprising. Te more basal position of Kunpania would be consistent with an older age for the unit from which it is known (Upper Quanzijie Formation; Angielczyk et al. 2021).

Jackknife resampling and/or Bremer supports reveal that many of the recovered clades in the analysis herein are unstable, including Bidentalia (recovered in <50 replicates, Bremer support value = 0.35), Cryptodontia (recovered in <50 replicates, Bremer support value = 1.864), Dicynodontoidea (recovered in <50 replicates, Bremer support value = 0.350), and Kannemeyeriiformes (recovered in 61 replicates, Bremer support value = 0.350).