A new dicynodont (Anomodontia: Emydopoidea) from the terminal Permian of KwaZulu-Natal, South Africa Christian F. Kammerer 1,2 § 1North Carolina Museum of Natural Sciences, 11 W. Jones Street, Raleigh, NC 27601 U.S.A. 2Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, WITS, Johannesburg, 2050 South Africa E-mail: christian.kammerer@naturalsciences.org Received 16 November 2018. Accepted 26 March 2019 INTRODUCTION Small dicynodonts (i.e. those with skull length <15 cm) are the numerically dominant tetrapods throughout most of the mid-to-late Permian strata in the Karoo Basin of South Africa. In the lowest strata of the Permo- Triassic Beaufort Group (those of the possibly Wordian Eodicynodon Assemblage Zone [AZ]), the most abundant taxon is the small basal dicynodont Eodicynodon oosthuizeni (Rubidge, 1990, 1995). In the subsequent Tapinocephalus AZ (Capitanian), the most abundant taxa are pylaecephalids, a group of small dicynodonts includ- ing Diictodon feliceps, Eosimops newtoni, Prosictodon dubei, and Robertia broomiana (Boonstra 1969; Angielczyk & Rubidge 2010, 2013; Smith et al. 2012; Day 2014). Diictodon in particular went on to extreme success even after the extinction of the other pylaecephalids, being far and away the most abundant tetrapod in the later Pristerognathus and Tropidostoma AZs (early Wuchiapingian) (Smith 1993). Recent research has suggested that the incredible abundance of Diictodon in these biozones indicates an unbalanced ecosystem (there are three times as many specimens of D. feliceps known from the Tropidostoma AZ as of all other taxa put together), and that D. feliceps may have been a disaster taxon flourishing in the wake of the mid-Permian mass extinction (much like Lystrosaurus following the end-Permian mass extinction) (Day et al. 2018). Unlike Lystrosaurus, however, which went extinct as soon as ecosystems began to recover in the Triassic, Diictodon continued to be a major component of later, more stable ecosystems: it remains the most abundant taxon in the later Wuchiapingian Cistecephalus AZ (Smith et al. 2012) and survived into the terminal Permian (Changhsingian) Daptocephalus AZ (Viglietti et al. 2016). Even discounting Diictodon, small dicynodonts were the numerically dominant tetrapods in most late Permian bio- zones: Pristerodon mackayi is the second-most abundant taxon in the Tropidostoma AZ and Cistecephalus microrhinus is the second-most abundant taxon in the Cistecephalus AZ, and other taxa such as Emydops arctatus are common com- ponents of both (Smith et al. 2012). Despite their earlier success, however, small dicynodont fortunes began to founder at the end of the Permian. Small dicynodonts make up only 19.2% of tetrapod specimens in the lower Daptocephalus AZ vs 40% for large dicyno- donts (taxa like Aulacephalodon, Daptocephalus, Dicynodon, and Oudenodon), and only 4% in the upper Daptocephalus AZ vs 64% large dicynodonts (including the aforemen- tioned taxa, but also a preponderance [34%] of the newly- appearing Lystrosaurus) (Viglietti et al. 2016). Several small dicynodont taxa (e.g. Compsodon, Digalodon) disappear at ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 179 A new taxon of dicynodont (Thliptosaurus imperforatus gen. et sp. nov.) is described based on a dorsoventrally-crushed skull from latest Permian (upper Daptocephalus Assemblage Zone) strata in KwaZulu-Natal, South Africa. Thliptosaurus is distinguished from all other dicynodonts by an elongate intertemporal bar with broad dorsal exposure of the parietals but apparently no pineal foramen. Absence of the pineal foramen in dicynodonts is exceedingly rare; the only other taxa which exhibit this feature either have substantially broader (Kawingasaurus fossilis) or narrower (Kombuisia frerensis) intertemporal regions. Inclusion of Thliptosaurus in a phylogenetic analysis of dicynodonts recovers it as a kingoriid emydopoid, a position supported by its anteriorly-restricted pterygoid keel, elongate, curved anterior process of the lacrimal, relatively posterior position of the median pterygoid plate, and occlusion of the mandibular fenestra by a lateral plate of the dentary. Intriguingly, even in the other kingoriids which retain a pineal foramen (Dicynodontoides spp. and Kombuisia antarctica), this structure is reduced in size relative to other dicynodonts, suggesting that the pineal eye was less important for thermoregulatory activity in this clade than in other anomodonts. Although part of a local fauna including taxa that are otherwise widespread in the Karoo Basin (Daptocephalus, Lystrosaurus), the unique presence of Thliptosaurus in the relatively poorly-sampled Daptocephalus Assemblage Zone deposits of KwaZulu-Natal suggests that this region may preserve endemic taxa, and should be prioritized for future fieldwork. Keywords: Synapsida, Dicynodontia, Permian, end-Permian mass extinction, South Africa. Palaeontologia africana 2019. ©2019 Christian F. Kammerer. This is an open-access article published under the Creative Commons Attribution 4.0 Unported License (CC BY4.0). To view a copy of the license, please visit http://creativecommons.org/ licenses/by/4.0/. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is permanently archived at: http://wiredspace.wits.ac.za/handle/10539/26708 Palaeontologia africana 53: 179–191 — ISSN 2410-4418 [Palaeontol. afr.] Online only ZooBank: urn:lsid:zoobank.org:pub:AC96C422-C4FC-4B96-9F45-599A3158EACB (http://www.zoobank.org) Permanently archived on the 9th of April 2019 at the University of the Witwatersrand, Johannesburg, South Africa. This article is permanently archived at: http://wiredspace.wits.ac.za/handle/10539/26708 http://creativecommons.org/licenses/by/4.0/ http://wiredspace.wits.ac.za/handle/10539/26708 mailto:christian.kammerer@naturalsciences.org https://orcid.org/0000-0002-0596-623X http://wiredspace.wits.ac.za/handle/10539/26708 http://www.zoobank.org the boundary between the lower and upper Daptocephalus AZ (Viglietti et al. 2016; Angielczyk & Kammerer 2017), and some of those that make it into the upper Dapto- cephalus AZ do not have ranges extending all the way to the Permo-Triassic boundary (PTB) (e.g. Diictodon; Retallack et al. 2003; Smith & Botha-Brink 2014). The only small dicynodont taxon whose range definitely extends to the PTB in South Africa is the kingoriid emydopoid Dicynodontoides recurvidens (Smith & Botha-Brink 2014), and it should be noted that the classification of this taxon as a ‘small dicynodont’ is somewhat questionable; although the majority of collected skulls are in the 10–15 cm range, it reached basal skull lengths of up to 24 cm (Angielczyk et al. 2009). Although small dicynodonts were clearly suffering in the lead-up to the PTB in the Karoo Basin, they were not totally extirpated at the end of the Permian, as small members of two emydopoid families (Kingoriidae and Myosauridae) are known from the earliest Triassic (Kombuisia antarctica from the Induan of Antarctica and Myosaurus gracilis from the Induan of Antarctica and South Africa; Hammer & Cosgriff 1981; Fröbisch et al. 2010). The Permian ancestry of these taxa is currently obscure: although Dicynodontoides and Kombuisia are sister-taxa (Fröbisch 2007; Kammerer et al. 2011), these two genera are so morphologically disparate that a direct ancestor–descendant relationship between the former and the latter is unlikely. Myosaurus is the only recognized myosaurid, and though the poorly-known late Permian taxon Emydorhinus (Broom 1935) may represent a related genus, the morphological gap between these taxa is not bridged by any known fossils in the Karoo record. Rather, as is also notably the case for the most successful group of Triassic dicynodonts, the Kannemeyeriiformes, it seems that the Permian antecedents of the small dicynodonts in the post-extinction recovery fauna must have been living outside of the well-sampled strata currently known from the Karoo Basin. Even within the Karoo Basin, it should be recognized that sampling of this interval is very uneven: the vast majority of studies are based on a few sections from the Eastern Cape Province and Free State (e.g. Smith 1995; Retallack et al. 2003; Ward et al. 2005; Smith & Botha-Brink 2014; Viglietti et al. 2016). By contrast, the fauna associated with the Permo-Triassic transition in KwaZulu-Natal is relatively poorly known (although the coeval flora is better sampled; Gastaldo et al. 2005). Oliviershoek Pass, a Lystrosaurus AZ-bearing site at the border between the Free State and KwaZulu-Natal, has been subject to several geological studies (e.g. Turner 1984, 1986) and occasional vertebrate fossil collection (see e.g. Brink 1965; Anderson & Anderson 1970; Rubidge 1997; Shishkin & Rubidge 2000), but this is an exception. The extensive but patchily-exposed Permo-Triassic rocks elsewhere in the province have garnered only rare histori- cal sampling (mostly by James Kitching; see e.g. Kitching 1968). Here I describe a new taxon of small dicynodont from latest Permian rocks in KwaZulu-Natal. This taxon is represented by only a single skull, so it does not alter the view of small dicynodonts as a declining percentage of faunas in the lead-up to the PTB. However, it does suggest that small dicynodont species richness in the terminal Permian was higher than previously thought, and points towards under-sampled regions like KwaZulu-Natal as a potential source of ‘missing diversity’ between the Permian and Triassic faunas. MATERIAL The specimen BP/1/2796 (in the collection of the Evolu- tionary Studies Institute [ESI], University of the Wit- watersrand, Johannesburg, South Africa) was collected by James Kitching in September 1958 in Stoffelton, northwest of Bulwer in western KwaZulu-Natal. This site encom- passes both latest Permian and earliest Triassic rocks of the Daptocephalus and Lystrosaurus AZs (Kitching 1968). Assemblage zone of origin is reflected in the preserva- tional style of the fossils from this locality: Permian bone (e.g. BP/1/2784, Daptocephalus leoniceps) is black-to-grey and preserved in grey matrix, whereas Triassic bone (e.g. BP/1/2793, Thrinaxodon liorhinus) is yellowish and preserved in red matrix (Kammerer, pers. obs.), as is seen in the transition from late Permian rocks of the Balfour Formation to those of the boundary-spanning Palingkloof Member elsewhere in the basin (Smith 1995). Despite the geographic and stratigraphic importance of this site, Kitching’s collections from Stoffelton have received little attention in the literature (and indeed much of this material remains unprepared). Durand (1991) described a complete skull of the large therocephalian Moschorhinus kitchingi (BP/1/2788) from the Daptocephalus AZ portion of this collection. Maisch (2002) described a small dicyno- dont skull (BP/1/2792), also from the Daptocephalus AZ portion of this collection, which he made the holotype of a new genus and species of basal lystrosaurid, Kwazulu- saurus shakai. BP/1/2796, the specimen described herein, was also collected in the Daptocephalus AZ strata. Based on the co-occurrence of Daptocephalus, Lystrosaurus, and Moschorhinus in this assemblage it can be recognized as belonging to the upper Daptocephalus AZ of Viglietti et al. (2016), the latest Permian fauna in South Africa. SYSTEMATIC PALAEONTOLOGY Synapsida Osborn, 1903 Therapsida Broom, 1905 Anomodontia Owen, 1860 Dicynodontia Owen, 1860 Emydopoidea van Hoepen, 1934 Kingoriidae King, 1988 Thliptosaurus imperforatus gen. et sp. nov. LSID. urn:lsid:zoobank.org:act:A9355D3F-A0BC-4790- BCCD-B8FC81AFB78F Holotype. BP/1/2796, a nearly complete but badly com- pressed skull and lower jaws. Type locality and horizon. Stoffelton, near Bulwer, KwaZulu-Natal, South Africa. Daptocephalus Assemblage Zone, Changhsingian, Permian. Etymology. Genus name meaning ‘compressed lizard’, from the ancient Greek èëéøéò (Latinized thlipsis) and 180 ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 ~ óáõñïò (Latinized saurus), in reference to the highly dorsoventrally compressed nature of the holotype. Also from thlipsis in the Biblical sense, in reference to the tribulations accompanying the End Times, alluding to the existence of this taxon immediately prior to the end-Permian mass extinction. Species name meaning ‘unpunctured’ in Latin, in reference to the great reduction (if not total absence) of the pineal foramen. Diagnosis. Emydopoid dicynodont characterized by the following combination of characters: absence (or extreme reduction) of the pineal foramen (otherwise only known in Kawingasaurus fossilis and Kombuisia frerensis among dicynodonts), moderately broad intertemporal bar (narrower than Kawingasaurus but broader than Kombuisia), absence of the postfrontal (synapomorphy of Kistecephalia), dentary plate occluding the mandibular fenestra (synapomorphy of Kingoriidae), arcing anterior process of lacrimal contacting nasal, eliminating contact between the maxilla and prefrontal (synapomorphy of Kingoriidae), broad, flat exposure of the parietals in the intertemporal bar (symplesiomorphy of Dicynodontia not present in Dicynodontoides or Kombuisia). DESCRIPTION The holotype and only known specimen of Thliptosaurus imperforatus (BP/1/2796) is a small skull (8.6 cm basal length; see Table 1) that has suffered extensive postmor- tem dorsoventral compression (Figs 1–5). It is nearly com- plete, although the suborbital portions of the zygoma and posterior edges of the temporal fenestrae have been reconstructed in plaster. The bone is light grey in colour and preserved in a grey siltstone matrix, like the other Daptocephalus AZ specimens from this locality (Kammerer, pers. obs.) Sutures on this specimen can be discerned dorsally (Fig. 1), but due to poor preservation and over- preparation are difficult to see on the lateral skull surface (Fig. 2). Preservation of the lower jaw in occlusion with the skull and its strong compression unfortunately obscures most of the palate, with only the pterygoids and basicranium clearly visible ventrally (Fig. 3). Only the ascending process of the premaxilla can be seen in BP/1/2796. Although transversely broad anteriorly, it tapers strongly posteriorly where it divides the nasals, terminating near the level of the anterior tip of the lacrimal (Fig. 1). The premaxilla is unpaired throughout its length. The external nares (and with them, the septo- maxillae) in this specimen cannot be discerned due to dorsoventral compression, but must have been present at the anterior tip of the snout, as they are clearly not located on the lateral face of the snout above the caniniform process. The maxilla is typical for dicynodonts, making up most of the lateral snout surface and bearing a distinct, ventrally-directed caniniform process (Fig. 2). The caniniform process is located in a very anterior position relative to the orbit (as in Dicynodontoides) and is tuskless. No other teeth are visible in this specimen, but overlap of the medial palatal portion of the maxilla by the lower jaw makes it impossible at present to be sure they were absent. The anterior margin of the caniniform process is longer and more gently sloping than the posterior margin, which rises steeply to contact the zygomatic arch. A postcanini- form keel appears to be present behind the left caniniform process, which is the better exposed of the two. Suborbi- tally the maxilla continues onto the zygomatic arch, but its posterior extent is uncertain due to plaster reconstruction on both sides of the skull; it is unknown whether it con- tacted the anterior zygomatic process of the squamosal. The nasal bosses are very similar to those of Dicynodon- toides: although distinctly expanded laterally near the snout tip, where they are separated by the premaxilla, they do unite posteromedially to form a single median swelling (Fig. 1A). The nasal bosses are heavily pitted or foraminated and weakly rugose. Posterior to the nasal boss, the nasal bone has a short length of flat, unorna- mented bone terminating near the anterior margin of the orbits in a nearly-straight suture with the frontal. The prefrontal and lacrimal are very similar to the condition in Dicynodontoides: the prefrontal is a short, roughly triangu- lar element at the anterodorsal corner of the orbit, but the lacrimal is very dorsoventrally thin and anteroposteriorly elongate, with a distinctly curved anterior process contacting the nasal and separating the maxilla from the prefrontal (Fig. 1B). The jugal is poorly exposed in this specimen, only being visible at the anteroventral corner of the right orbit, anterolateral corner of the temporal fenestra (Fig. 1), and forming the lateral rim of the subtemporal fenestra ventrally (Fig. 3). The zygomatic ramus of the squamosal makes up all of the subtemporal bar in lateral view; this ramus is dorsoventrally extremely thin and transversely broad (although this has likely been exaggerated by taphonomic compression). The occipital ramus of the squamosal is mostly missing in this specimen (and replaced by plaster). Its ventrolateral corner is intact on both sides, however, and show that it was broad and plate-like posteriorly as in most other dicynodonts (Fig. 4). It bears a dorsoventral depression immediately lateral to its contact with the paroccipital process of the opisthotic. The frontal is a very large bone in Thliptosaurus, and forms almost the entirety of the interorbital region and part of the intertemporal region (Fig. 1). The frontal forms most of the dorsal margin of the orbit and is transversely ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 181 Table 1. Cranial measurements of BP/1/2796, holotype of Thliptosaurus imperforatus. BSL = 8.6 cm DSL = 8.1 cm (assuming plaster reconstruction is accurate) Snout length = 2.4 cm Interorbital width = 1.7 cm Anterior intertemporal width = 2.5 cm Posterior intertemporal width = 2.1 cm Median pterygoid plate width = 0.5 cm Anterior pterygoid keel height = 0.6 cm Anterior pterygoid ramus height = 0.4 cm Anterior pterygoid process length = 2.0 cm Quadrate pterygoid process length = 1.2 cm Pre-median pterygoid plate length of skull = 6.2 cm Post-median pterygoid plate length of skull = 2.4 cm Dentary symphysis height = 2.0 cm Dentary ramus height = 1.5 cm Postdentary bone height (left side) =1.0 cm Temporal fenestra length (left side, more complete) = ~3.5 cm ~ 182 ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 Figure 1. Holotype of Thliptosaurus imperforatus (BP/1/2796) in dorsal view: A, photograph; B, interpretive drawing (grey indicates matrix, hatching indicates plaster reconstruction). fr, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; pa, parietal; pmx, premaxilla; po, postorbital; pp, preparietal; prf, prefrontal; sq, squamosal. Scale bar equals 1 cm. broadest just anterior to the postorbital bar. Posteriorly, the frontal forms a ragged, tapering process extending between the preparietal and postorbital and dividing the anterior margin of the parietal at tip. The preparietal is a narrow, lozenge-shaped median element that is flush with the surrounding frontals and parietals. No postfrontal is present; as is typical for kistecephalian emydopoids (Kammerer & Angielczyk 2009), the region where the postfrontal occurs in other dicynodonts is occupied by an anterior portion of the postorbital. It is possible that this is the result of fusion between the postfrontal and postorbital during development, but at present no juve- nile kistecephalians showing separation between these elements have been found, unlike the situation in geikiids (Kammerer & Smith 2017) and kannemeyeriiforms (Angielczyk et al. 2018) in which juveniles with at least partially discrete postfrontals are known. The postorbital forms the anteroposteriorly thin postorbital bar ventrally, which makes up the posterior margin of the orbit. Dorsally, it forms a posteriorly-directed process rimming the medial edge of the temporal fenestra. The postorbital has a broad, nearly-horizontal dorsal exposure in the intertemporal bar that is offset nearly perpendicularly from the portion of the postorbital making up the wall of the temporal fenestra. This dorsal exposure of the post- orbital bears an elongate, posteriorly-tapering depression (originating immediately behind the postorbital bar and terminating at roughly two thirds of the length of the temporal fenestra). This depression would have served as the attachment site for the M. adductor mandibulae externus medialis (Angielczyk et al. 2018). The parietal is a broad, flat bone exposed dorsally in the posterior intertemporal bar. Anteromedially it contacts the preparietal and anteriorly its margin is split in two by the posterior process of the frontal. Highly unusually for a dicynodont, the mid- parietal suture appears to extend uninterrupted through- out its length, i.e. there is no pineal foramen apparent. There is a darkened area of the suture at about the midlength of the intertemporal bar (Fig. 1A), but careful microscopic examination of this area suggests that this represents discoloration of the parietal edge and some adhered matrix. If a pineal foramen is present in this region (e.g. obscured by compression of the specimen), it would have to be exceedingly narrow and slit-like and also separated from the preparietal by a substantial length (0.6 cm, 21% of the length of the intertemporal bar), an extreme rarity among dicynodonts. As mentioned above, little of the palate is exposed on this specimen. The anterior pterygoid rami are elongate and narrow, with the pterygoid keel restricted to their anterior tip (Fig. 3). The anterior rami are nearly straight, as in Compsodon and Dicynodontoides (Angielczyk & Kammerer 2017). The anterior rami do not seem to con- verge into a median ridge posteriorly, but as the median pterygoid plate is damaged this is uncertain. The quadrate rami of the pterygoid are relatively short (1.2 cm in length, vs 2.0 cm for the anterior rami) and extend towards the quadrate at an angle of ~60° relative to the long axis of the skull (65° on the right side, 56° on the left with differences due to compression), giving the median pterygoid plate a relatively posterior position on the skull. The basal tubera are anteroposteriorly elongate, with the parabasisphe- noid contribution greater than that of the basioccipital. No intertuberal ridge is present. The quadrate-quadratojugal complex forms an expanded plate at the anteroventral edge of the squamosal, as is typical for dicynodonts. The occiput is very poorly preserved and no sutures can be delimited, but what is visible is standard for dicynodonts, with a large, tripartite occipital condyle and dorsoven- trally expanded paroccipital process of the opisthotic extending laterally and ventrally (Fig. 4). The posterior tip of the paroccipital process is broken off, so the possibility that it had a sharp posterior process as in other emydo- poids cannot be excluded. The dentary symphysis of the lower jaw is long (Fig. 5), with an elongate anterodorsal end ending in a flattened, shovel-like beak tip. There is a weak ridge along the lateral edge of the anterior face of the symphysis. The ventral edge of the jaw symphysis is made up an attenuate anterodorsal process of the fused splenial. No angular contribution to the symphysis is present. Laterally, the dentary forms a tall plate obscuring the mandibular fenestra, a feature otherwise known only in Dicynodon- toides (in which it partially covers the fenestra) and Kombuisia (in which the fenestra is covered completely) among dicynodonts (Fröbisch 2007). The exact degree of occlusion is uncertain, however, due to adhering matrix on the surface of the angular. The dentary of Thlipto- saurus is unusual in seeming to have a relatively short dorsal (coronoid) process overhanging the surangular; in Dicynodontoides and Kombuisia this process extends far posterior to the ventral margin of the dentary (Cluver & King 1983; Fröbisch 2007; Fröbisch et al. 2010). However, it is possible that the dentary extends further postero- dorsally but is obscured by matrix. A weak antero- posteriorly-oriented ridge is present at midheight on the left dentary ramus, representing a greatly reduced lateral dentary shelf. The angular has two broad, concave lateral exposures on the jaw: one anterior to the reflected lamina, forming the ventral edge where the mandibular fenestra ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 183 Figure 2. Holotype of Thliptosaurus imperforatus (BP/1/2796) in (A) right lateral and (B) left lateral views. Scale bar equals 1 cm. 184 ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 Figure 3. Holotype of Thliptosaurus imperforatus (BP/1/2796) in ventral view: A, photograph; B, interpretive drawing (grey indicates matrix, hatching indicates plaster reconstruction). an, angular; apt, anterior pterygoid ramus; ar-pr, articular-prearticular complex; bt, basal tuber; de, dentary; fo, fenestra ovalis; j, jugal; mpt, median pterygoid plate; mx, maxilla; oc, occipital condyle; op, opisthotic; pl, palatine; pmx, premaxilla; qpt, quadrate pterygoid ramus; sp, splenial; sq, squamosal; v, vomer. Scale bar equals 1 cm. would normally be in a dicynodont, and one posterior to the reflected lamina, separating it from the articular region of the jaw. Only the base of the reflected lamina is preserved; it was anteroposteriorly short, similar in proportions to that of Dicynodontoides (Cox 1959). The surangular is exposed as a narrow strip running along the dorsal margin of the jaw ramus in the postdentary region. The articular has a curved, convex dorsal surface fitting between the ventral condyles of the quadrate and extend- ing beyond them (to allow palinal jaw motion). The articu- lar ends ventrally in a short, blunt retroarticular process. Medially, the prearticular is visible as a thin lamina making up part of the jaw surface, but is preserved too poorly to note any further detail. PHYLOGENETIC ANALYSIS Thliptosaurus imperforatus was coded into the most recent phylogenetic analysis of anomodonts (Kammerer 2018; based on the revised analysis of Angielczyk & Kammerer 2017). The dataset consists of 105 OTUs (98 anomodont taxa and 7 non-anomodont therapsids, with Biarmosuchus tener used as outgroup) with 23 continuous and 174 discrete state characters. Seven discrete state characters were treated as ordered (characters 58, 61, 79, 140, 150, 151, 166), following Angielczyk & Kammerer (2017). Continuous characters were treated as additive using the methodology of Goloboff et al. (2006). Revised codings for Sangusaurus parringtonii were included based on the analysis of Angielczyk et al. (2018). The dataset was analysed using TNT v1.1 (Goloboff et al. 2008) using New Technology methods (tree drifting, parsimony ratchet, and tree fusing) on a driven search (initial search level = 65, checked every three hits) required to find the shortest tree at least 20 times. Symmetric resampling analysis was done on 1000 replicates and Bremer values were calcu- lated using the bremer.run script in TNT based on stored trees suboptimal by 20 steps. Three most parsimonious trees of length 1146.601 were recovered, with a consistency index of 0.241 and retention index of 0.716. A consensus tree showing the results of the phylogenetic analysis is presented in Fig. 6. In general, tree topology is similar to that of Angielczyk & Kammerer (2017), Olroyd et al. (2017), Angielczyk et al. (2018), and Kammerer (2018). Like these recent topologies (and unlike a number of previous analyses based on earlier versions of the data matrix; e.g. Kammerer et al. 2011, 2013, 2015a, 2016; Castanhinha et al. 2013; Cox & Angielczyk 2014; Angielczyk et al. 2016; Kammerer & Smith 2017), Pylaecephalidae is recovered outside of Therochelonia. Bidentalian topology remains volatile. Although a mono- phyletic Cryptodontia (as in Kammerer 2018) is not recov- ered; a ‘partial Cryptodontia’ made up of Rhachio- cephalidae+Geikiidae is found, unlike in the analyses of Angielczyk & Kammerer (2017), Olroyd et al. (2017), and Angielczyk et al. (2018) in which Geikiidae, Rhachio- cephalidae, and Oudenodontidae formed successive sister-taxa to the main dicynodontoid radiation (with Idelesaurus and Odontocyclops as wildcard taxa either recovered as basal geikiids or outside Geikiidae+‘tradi- tional’ dicynodontoids). Within Dicynodontoidea, the only result of note is the recovery of a clade made up of Lystrosauridae (here restricted to Lystrosaurus) and various ‘Dicynodon-grade’ taxa (Daptocephalus, Delecto- saurus, Dicynodon, Dinanomodon, Peramodon, Turfanodon, Vivaxosaurus). The latter group could be recognized as Dicynodontidae if supported by future analyses, with the caveat that dicynodontoid phylogeny needs intense further research before the position of any of the Permian taxa can be considered stable. Intriguingly, an expansive version of the clade Endo- thiodontia (sensu Kammerer & Angielczyk 2009) is recov- ered, in which Pristerodon, Brachyprosopus, and endothio- dontids (Niassodon+Endothiodon) form successive out- groups to Emydopoidea (sensu Kammerer et al. 2015a). Within Emydopoidea, Thliptosaurus is recovered as a kingoriid outside of the clade Dicynodontoides+Kombuisia, and Kingoriidae is recovered within Kistecephalia (like most recent analyses, but unlike that of Olroyd et al. 2017, where they fell outside of Emydops+Kistecephalia). Oddly, Myosaurus is recovered as the sister-taxon of Kingoriidae; this taxon is usually recovered as the sister- taxon of Cistecephalidae (e.g. Kammerer et al. 2011; Angielczyk & Kammerer 2017; Olroyd et al. 2017; Angielczyk et al. 2018; although see Angielczyk & Kurkin 2003). It must be noted, however, that support for the expansive Endothiodontia and a Myosauridae+Kingorii- dae relationship is extremely low (<50 resampling support and <1 Bremer support), requiring only a frac- tional step to revert to the prevailing topology. DISCUSSION Taxonomic distinction of Thliptosaurus The compressed state, small size, and singleton nature of BP/1/2796 raise the question of whether its distinctive features could be the result of ontogenetic and/or tapho- nomic variation. Discrete characters such as the absence of the pineal foramen and occlusion of the mandibular fenestra by the dentary are not known to be variable with ontogeny in dicynodonts. However, intertemporal width is notably ontogenetically variable in this clade (Kammerer et al. 2011, 2015b), and it is conceivable that compression could obscure the pineal foramen in a taxon in which it is already small. As such, further comparison with other kingoriids (the only dicynodont clade in which ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 185 Figure 4. Holotype of Thliptosaurus imperforatus (BP/1/2796) in occipital view. Scale bar equals 1 cm. the mandibular fenestra is occluded, whose members also tend to have small pineal foramina; see below) is warranted. Of particular import in this regard is Dicyno- dontoides, which also occurs in rocks of latest Permian age (Smith & Botha-Brink 2014). BP/1/2796 can readily be distinguished from both species of Kombuisia based on intertemporal morphology. The intertemporal region in Kombuisia is generally narrow and very sharply constricted near its posterior end (Fröbisch 2007; Fröbisch et al. 2010). The parietals of Kombuisia are exposed as only a thin sliver between the large, overlap- ping postorbitals, unlike in BP/1/2796 where they are broadly exposed (Fig. 7). Furthermore, the holotype of Kombuisia frerensis (Fig. 7B), which shows the most extreme narrowing of the intertemporal bar in the genus, is both slightly smaller (7.7 cm basal length) than and just as dorsoventrally crushed as BP/1/2796 (Fröbisch 2007). Comparisons with similarly-sized and preserved speci- mens of Dicynodontoides also indicate that their differences from BP/1/2796 are not attributable to ontogenetic or taphonomic variation. USNM 25176 (in the collections of the National Museum of Natural History, Washington DC, U.S.A.) is a small skull (9.6 cm basal length) of D. recur- videns from Doornplaas, Graaff-Reinet (Fig. 7C). Although only slightly larger than BP/1/2796, it already exhibits the comparatively narrow intertemporal bar typical of larger Dicynodontoides specimens, with broad overlap of the parietals by the postorbitals (as in Kombuisia). Nor can taphonomic distortion explain differences in intertem- poral proportions between BP/1/2796 and Dicynodontoides. BP/1/22 is another skull of D. recurvidens from Doornplaas, which has experienced extreme dorsoventral crushing (Fig. 7D) comparable to that of BP/1/2796, yet its inter- temporal bar is recognizably more similar to the some- what laterally-compressed USNM 25176 than to BP/1/2796. Also of note is that the pineal foramina remain evident despite distortion in both USNM 25176 and BP/1/22, and dorsoventral compression is unlikely to obscure this foramen in any case (although extreme lateral compression could do so). Given these consistent differ- ences between BP/1/2796 and other kingoriids, it is here considered justified to establish a new taxon (Thlipto- saurus imperforatus) for the former despite the crushed state of the holotype. A final point of consideration is whether BP/1/2796 represents the adult of a late-surviving small-bodied dicynodont taxon (as argued here) or is a juvenile for which the adult morphology is currently unknown. Although a definite answer is not possible in the absence of further material, several features suggest that BP/1/2796 is indeed a mature individual. The snout in BP/1/2796 is well-ossified, with none of the fontanelles or irregu- lar sutures observed in juveniles of larger dicynodonts (e.g. Kammerer et al. 2015b). There is no evidence of a postfrontal bone in BP/1/2796; loss of this bone is usually interpreted as occurring via fusion with the postorbital during ontogeny (Kammerer & Smith 2017). Finally, the preparietal of BP/1/2796 is small relative to skull size. 186 ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 Figure 5. Holotype of Thliptosaurus imperforatus (BP/1/2796) in left lateral view; detail illustrating mandibular morphology. A, Photograph; B, interpre- tive drawing (grey indicates matrix). an, angular; ar, articular; de, dentary; lds, lateral dentary shelf; rla, reflected lamina of angular; sa, surangular; sp, splenial. Scale bar equals 1 cm. Juvenile dicynodonts usually have proportionally large preparietal bones (Kammerer et al. 2011; see also Fig. 7C), but this bone is relatively small in most dicynodont adults (with some exceptions, e.g. Diictodon), including other emydopoids (see Fig. 7B). Pineal foramen reduction in Kingoriidae Loss of the pineal foramen is a very rare occurrence within Anomodontia, and previously characterized only the cistecephalid Kawingasaurus fossilis (Laaß 2014) and the kingoriid Kombuisia frerensis (Fröbisch 2007) (i.e. only ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 187 Figure 6. Results of the phylogenetic analysis. Thliptosaurus imperforatus highlighted in bold. Numbers at nodes represent symmetric resampling values (above nodes) and Bremer supports (below nodes). Resampling values <50 and Bremer values <1 not shown. Higher taxa of importance vis-à-vis Thliptosaurus are labelled. in these taxa do all known specimens lack the pineal fora- men. Rare intraspecific variability in presence/absence of the foramen has also been reported by Benoit et al. 2016 for Cistecephalus, Diictodon, Lystrosaurus, and Oudenodon. It should be noted that the available samples for both Ka. fossilis and Ko. frerensis are very small, however, so potential variability in this feature is uncertain.) Although only absent in Kombuisia frerensis and Thliptosaurus imperforatus, the pineal foramen is also reduced in all other known kingoriids: in Kombuisia antarctica it is present as only a narrow slit (Fröbisch et al. 2010) and in both species of Dicynodontoides it is relatively small (compared to other dicynodonts) and seemingly constricted by the medial expansions of the postorbitals (Cox 1959). In other dicynodonts in which the intertemporal bar is very narrow, with the postorbitals overlapping the parietals, the pineal foramen is usually positioned right behind the postorbital bars, with the constricted portion of the intertemporal bar occurring posteriorly (e.g. Dapto- cephalus, Dicynodon; Kammerer et al. 2011). In Dicyno- dontoides, however, the pineal foramen is near the mid-length of the intertemporal bar (Angielczyk et al. 2009), in the area where overgrowth of the postorbitals reduces dorsal exposure of the parietals to a thin crest. In extant reptiles, the pineal complex (pineal eye and/or gland) is involved in thermoregulation, with the pineal gland producing melatonin governing thermoregulatory behaviours (e.g. basking) and circadian rhythms (Under- wood 1990). A pineal foramen housing a pineal eye, as would have been the case in most dicynodonts, is retained in Sphenodon and a variety of lizards, whereas only the underlying pineal gland (covered by the parietal bones) is present in turtles and snakes (the pineal complex is absent altogether in crocodilians) (Tosini 1997). A pineal gland, but no pineal eye, is also present in modern mammals, and loss of the pineal foramen is recognized as a syn- apomorphy of probainognathian cynodonts (Hopson & Kitching 2001). Benoit et al. (2016) recently reviewed the distribution of pineal foramina in therapsids leading up to its loss, and noted convergent reduction of this feature in both therocephalians and cynodonts during the Permo- Triassic transition. They argued that this loss could have been correlated with the evolution of endothermy in Therapsida, potentially involving convergent origins of endothermy in cynodonts and therocephalians. Benoit et al. (2016) also considered the possibility that environmental changes leading into the Triassic (such as increased global temperatures and continental drift towards the equator) could have led to decreased impor- tance of the pineal eye in therapsid thermoregulation. In extant lizards, there is a trend towards reduction or loss of the pineal eye towards the equator, as precise monitoring of daylight and seasonal cycles is less important for ecto- therms in the warm tropics (Gundy et al. 1975). However, Benoit et al. (2016) disfavoured this explanation because of diachronous patterns of reduction in therocephalians vs 188 ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 Figure 7. Kingoriids compared in dorsal view. A, BP/1/2796, holotype of Thliptosaurus imperforatus. B, BP/1/5344, holotype of Kombuisia frerensis. C, USNM 25176, referred specimen of Dicynodontoides recurvidens. D, BP/1/22, referred specimen of Dicynodontoides recurvidens. Scale bars equal 1 cm. cynodonts and the apparent absence of this pattern in coeval dicynodonts and gorgonopsians. Nevertheless, the presence of a similar pattern in Kingoriidae, a dicynodont clade noted for crossing the Permo-Triassic boundary, suggests that they may have been overly hasty in discounting this hypothesis (the extinction of gorgonopsians at the end of the Permian also makes their retention of a pineal eye something of a moot point). Canalized absence of the pineal foramen in Probaino- gnathia may well have been related to the origin of endothermy, but the possibility that the original reduc- tion of the foramen was driven by environmental pres- sures in mesothermic ancestors deserves additional consideration. Small dicynodonts at the Permo-Triassic boundary and their distribution Thliptosaurus joins a highly restricted contingent of small dicynodonts in the latest Permian. Within the Karoo Basin, Dicynodontoides, Diictodon, Emydops, Emydorhinus, and Pristerodon have been recorded in the upper Daptocephalus AZ (Viglietti et al. 2016). However, Diictodon is limited to the lowest part of the upper Daptocephalus AZ, and the other taxa are represented by very little and some- times questionable material. Viglietti et al. (2016, supple- mental material) noted that BP/1/89, the sole upper Daptocephalus AZ record of Emydops arctatus, was from a locality whose precise stratigraphy was ‘unreliable but most likely Upper DAZ’. Dicynodontoides and Emydorhinus are also known from only single specimens in the upper Daptocephalus AZ. The only record of Pristerodon from the upper Daptocephalus AZ is erroneous, and instead comes from Tropidostoma AZ rocks in Esterville (P. Viglietti, pers. comm., 2018). Outside of the Karoo Basin, latest Permian dicynodonts are known from China and Russia, and also show a paucity of small-bodied taxa. In China, the Cangfanggou Group of the Junggur Basin has yielded numerous fossils of ‘Dicynodon-grade’ Permian dicyno- dontoids (e.g. Jimusaria) and Lystrosaurus (Metcalfe et al. 2009; Kammerer et al. 2011), but only a single small dicynodont skull, representing the sole extra-African record of Diictodon (Angielczyk & Sullivan 2008). Changhsingian dicynodont records of any kind are rare in Russia, but there as well, small taxa (Delectosaurus, Elph, and Interpresosaurus) seem to be rarer than larger dicyno- dontoids (e.g. Vivaxosaurus) (Angielczyk & Kurkin 2003; Kurkin 2011). Smith & Botha-Brink (2014) argued that the first phase of the end-Permian mass extinction in the Karoo Basin coincided with lowering of the water table, reducing the vegetative groundcover upon which small dicynodonts fed. It is uncertain whether similar environmental factors were driving small dicynodont decline outside of the basin. Clearly, however, small dicynodont habitat was not totally eliminated, as some small dicynodonts survived into the Early (Myosaurus gracilis) and Middle Triassic (Kombuisia frerensis) of South Africa. Fröbisch et al. (2010) suggested that Antarctica might have acted as a refugium for small dicynodonts during this time. They noted that kingoriids are present in South Africa in the late Permian and Middle Triassic, but while missing in the South Afri- can Early Triassic recovery fauna, they are present in coeval beds in the Antarctic Fremouw Formation. Further sampling is required to test this hypothesis (unfortu- nately, pre-Triassic vertebrate fossils have not yet been found in the Fremouw Formation), but the idea of geo- graphically variable survival of small dicynodonts during this time is worth considering. Although faunal variation between the successive Permo-Triassic assemblage zones in the Karoo Basin has been studied for over a century (see review in Rubidge 1995), relatively little attention has been given to geo- graphic variation within the assemblage zones. In part, this is due to the tight correlation between geography and stratigraphy: because of the original depositional and subsequent erosional history of the basin, older assem- blage zones are mainly exposed in the south and west (with the oldest Eodicynodon AZ being limited to a thin strip at the southwestern edge of the basin) (Catuneanu et al. 2005; Smith et al. 2012). However, the later Dapto- cephalus–Cynognathus AZs are exposed as broadly concen- tric rings surrounding the Triassic-Jurassic Stormberg Group (centred in Lesotho), giving them expansive coverage in the Eastern Cape, Free State, and KwaZulu- Natal (with Daptocephalus AZ exposures also appearing in the Western Cape and Mpumalanga) (van der Walt et al. 2010). There has been intense recent debate in the Permo- Triassic extinction literature focusing on geographic variation in lithology and paleobotanic records, with potential implications for the uniformity of the PTB event bed across the basin (Gastaldo et al. 2009, 2017; Gastaldo & Neveling 2012; Ward et al. 2012). However, even these studies were quite limited in their geographic coverage (largely re-examining classic PTB sites in the Free State and Eastern Cape) and incorporated little data concerning the distribution of vertebrate fossils. Kammerer et al. (2015a) noted that within the Dapto- cephalus AZ, some taxa seem to be restricted to the area surrounding Graaff-Reinet (near the boundary between the Eastern and Western Cape provinces), but were uncer- tain whether this represents real geographic endemism or local exposure of a particular time slice. More extensive stratigraphic study (Viglietti et al. 2016) has resolved at least some of this variation between localities as faunal turnover between the lower and upper Daptocephalus AZ, but not all of it; nor does this explain the presence of some therapsid taxa with very limited records in South Africa that are more abundant in probable coeval beds in Zambia (see e.g. Angielczyk & Kammerer 2017). Historically, the Permo-Triassic therapsid fauna from KwaZulu-Natal seemed unremarkable, with published records largely representing common taxa known elsewhere in the basin (e.g. Daptocephalus [Ewer 1961]; Lystrosaurus [Broom 1907; Haughton 1917; Kitching 1968]; Moschorhinus [Brink 1959; Durand 1991]). However, these records only scratch the surface: as the index taxa for their assemblage zones, taxa like Daptocephalus and Lystrosaurus are expected to be present throughout the basin. It is the rarer taxa that are of greater interest, and in this regard Thliptosaurus is intrigu- ing, as a new, small-bodied, latest Permian dicynodont. ISSN 2410-4418 Palaeont. afr. (2019) 53: 179–191 189 Considering how well-sampled coeval strata are else- where in the basin, discovery of a new South African dicynodont taxon of this age is surprising. A second small dicynodont taxon (Kwazulusaurus) is also known only from the Stoffelton locality (although the distinction of this genus from Lystrosaurus requires additional study), suggesting that the second-order components of this fauna may differ markedly from those in their better- sampled western counterparts. Further study of this local- ity is clearly needed, and in general, end-Permian and earliest Triassic exposures in KwaZulu-Natal should be a priority for future fieldwork in the region. I thank Sifelani Jirah for access to the ESI dicynodont collections, Kelsey Glennon and Jonah Choiniere for hosting my stay at the University of the Witwatersrand, and Jörg Fröbisch and Roger Smith for their helpful reviews. My research on Permo-Triassic tetrapods has been supported by a grant (KA 4133-1/1) from the Deutsche Forschungsgemeinschaft. §ORCID iD C.F. Kammerer: orcid.org/0000-0002-0596-623X REFERENCES ANDERSON, H.M. & ANDERSON, J.M. 1970. 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