Cranial morphology of the middle Permian pareiasaurNochelesaurus alexanderifrom the Karoo Basin of South Africa

Abstract

Pareiasaurs were globally distributed, abundant, herbivorous parareptiles with the basal-most members found only in the mid-Permian of South Africa. These basal forms form a monophyletic group and were locally abundant and became extinct at the top of the Tapinocephalus Assemblage Zone at the end of the Guadalupian. Four species of basal pareiasaurs are currently recognised: Bradysaurus baini, B. seeleyi, Embrithosaurus schwarzi and Nochelesaurus alexanderi, but they are all poorly understood and there remains historic uncertainty as to their validity. In this paper, our second contribution designed to improve understanding of the basal group, we present the first detailed cranial description and updated diagnosis for Nochelesaurus alexanderi and demonstrate that it is a distinct taxon based on one cranial autapomorphy, a large transversely wide postparietal, and a combination of cranial characters. Within the local group of mid-Permian pareiasaurs, we recognise new dental features of Nochelesaurus alexanderi: non-symmetrical marginal cusp arrangements on upper and lower teeth resulting from an extra basal mesial cusp; an incipient horizontal cingulum on lower jaw teeth, sometimes with one or two tiny medial cingular cusps; and up to ten marginal cusps. Our study demonstrates that tooth morphology and orientation, cranial ornamentation, morphology of the cheek bosses, shape of the postfrontal and postparietal, and morphology of the distal paroccipital process of the opisthotic are the most useful to identify South African mid-Permian pareiasaurs.

The Brazilian Pareiasaur Revisited

“…The posterior cervicals (3rd, 4th, and 5th) are peculiar in that they do not have distinct diapophyses and parapophyses, contrasting with the condition described in other pareiasaur species, where these processes are separated (Boonstra, 1934c;Benton, 2016;Van den Brandt et al, 2021a). In the vertebra identified as the third cervical, the fused parapophysisdiapophysis forms a transverse process that has the shape of a minute triangular wing, with a lateroventrally oriented dorsal surface and a laterodorsal facet for articulation with a holocephalous rib (Figures 7I,J).…”

“…Provelosaurus americanus was re-coded for 31 character states. Shihtienfenia permica was re-coded for characters 90 and 91 following (Benton, 2016) and Bradysaurus baini was modified for character 125 after ( Van den Brandt et al, 2021a). Three new characters were included in the data matrix.…”

“…The shape and proportions of the squamosal are distinctive in the Brazilian pareiasaur. Most pareiasaur species have squamosals in which the dorsoventral and anteroposterior dimensions are roughly equal (Boonstra, 1934a;Lee, 1997a;Tsuji, 2013;Van den Brandt et al, 2019), giving this bone an almost square shape in lateral view, and in the genera Nochelesaurus and Pareiasuchus, the anteroposterior dimension exceeds the ventrodorsal one (Lee et al, 1997;Van den Brandt et al, 2021b). An exception is Arganaceras vacanti from Morocco (Jalil and Janvier, 2005), a pareiasaur that also features a dorsoventrally expanded squamosal albeit lacking the prominent posterior boss present in the Brazilian species.…”

“…Most pareiasaurs possess cylindrical angular bosses with a main axis that is perpendicular to the tooth row in lateral view. Other pareiasaurs such as Embrithosaurus schwarzi and Nochelesaurus alexanderi (Van den Brandt et al, 2019Brandt et al, , 2021b, show some degree of posterior inclination of the angular boss but this condition is limited to the apex, being mostly cylindrical in lateral view, rather than triangular as in the Brazilian taxon. Furthermore, the bosses of these Karoo species are curved medially, a condition that contrasts with Provelosaurus americanus.…”

“…Small forms like Nanoparia luckhoffi were size-equivalent to a living giant armadillo and large species such as Bradysaurus baini and Scutosaurus karpinskii had a mass comparable to a domestic bull, the latter with an estimated weight of up to 1.5 tons (Romano et al, 2021). They have been recorded in Brazil (Araújo, 1985b;Cisneros et al, 2005), South Africa (Rubidge, 2005;Van den Brandt et al, 2021a), Zambia (Lee et al, 1997), Niger (Tsuji et al, 2013), Tanzania (Maisch and Matzke, 2019), Morocco (Jalil and Janvier, 2005), Scotland (Spencer and Lee, 2000), Germany (Tsuji and Müller, 2008), Italy (based on footprints, Leonardi et al, 1974), Russia (Ivakhnenko, 1987;Bulanov and Yashina, 2005;Tsuji, 2013), and China (Li and Liu, 2013;Xu et al, 2014;Benton, 2016;Liu and Bever, 2018). Despite being relatively common in the geological record, specially in the Karoo Basin, their taxonomy and interrelationships have long been problematic, in part because their cranial sutural patterns are typically obscured by thick ornamentation.…”