Widespread azendohsaurids (Archosauromorpha, Allokotosauria) from the Late Triassic of western USA and India

Abstract

Archosauromorph reptiles underwent rapid lineage diversification, increases in morphological and body size disparity, and expansion into new adaptive landscapes. Several of the primary early archosauromorph clades (e.g. rhynchosaurs) are easy to differentiate from others because of their characteristic body types, whereas the more lizard‐like and carnivorous forms with long necks (e.g. tanystropheids) were historically all relegated to the groups Protorosauria or Prolacertiformes. However, it is now clear that these groups are polyphyletic and that a lizard‐like, carnivorous form is plesiomorphic for Archosauromorpha, and multiple subclades started with that body plan. Among these early forms is Malerisaurus from the Upper Triassic of India (M. robinsonae) and the Upper Triassic of south‐western USA (M. langstoni). In this paper, we critically re‐evaluate the genus. We find both species of Malerisaurus as valid, and identify Malerisaurus as an early diverging, but late‐surviving, carnivorous member of Azendohsauridae within Allokotosauria. Our histological analysis and assessment of ontogenetic changes of limb bones of small and large individuals demonstrate that the skeletons of the small forms grew slowly and became more robust through ontogeny, and that the larger recovered bones are at or near the maximum size of the taxon. Malerisaurus and Malerisaurus‐like taxa were common members of the Otischalkian–Adamanian (late Carnian to mid‐Norian) faunal assemblages from Upper Triassic strata of the south western USA, but they are absent from the younger Revueltian holochronozone. Specimens from western North America show that Allokotosauria had a near‐Pangaean distribution for much of the Middle Triassic to Late Triassic.

Puercosuchus traverorum n. gen. n. sp.: a new malerisaurine azendohsaurid (Archosauromorpha: Allokotosauria) from two monodominant bonebeds in the Chinle Formation (Upper Triassic, Norian) of Arizona

“…The anterior teeth are the largest and are slightly procumbent (Fig. 3.3,3.4), similar to those of Azendohsaurus madagaskarensis (FMNH PR 2751) and other malerisaurines (e.g., TTU-P 11212;Nesbitt et al, 2021). The premaxillary teeth are sub-elliptical to sub-circular in cross section at the base but taper labiolingually apically.…”

“…A stratigraphic section was measured and described near PFV 217 from the Newspaper Rock Bed (sensu Parker, 2006;Martz and Parker, 2010) to the lowest unit of the Sonsela Member using a Precision Jacob's staff (ASC Scientific), Brunton pocket transit, and Munsell Rock Color Book. Malerisaurus-like azendohsaurids, in a recent study (Nesbitt et al, 2021) we proposed a new genus to avoid inferring phylogenetic relationships through taxonomy. In that study (Nesbitt et al, 2021, p. 5, fig.…”

“…Despite extensive excavation and screen-washing of matrix removed from numerous field jackets, there is no evidence of a second allokotosaur (e.g., teeth of Trilophosaurus Case, 1928) at the site. Where they are present, there appears to be only one taxon of malerisaurine azendohsaurid in any given assemblage, and most of the variation across elements relates to ontogenetic changes (Nesbitt et al, 2021), especially regarding a significantly larger cervical vertebra that was surface collected from PFV 217 decades earlier (PEFO 16733;Fig. 1.5).…”

“…focusing on the PEFO specimens, supplemented with those from the Krzyzanowski bonebed. Most anatomical comparisons are made with respect to other azendohsaurid allokotosaurs, but additional comparisons of malerisaurine azendohsaurids to other archosauromorphs are provided by Nesbitt et al (2021). All vertebrae were found disarticulated; their positions in the presacral column are estimated based on information from other archosauromorphs.…”

“…Azendohsaurids are a clade of Middle-Late Triassic allokotosaurian non-archosaur archosauromorphs (Nesbitt et al, 2015) that until recently only included the herbivorous Azendohsaurus laaroussii Dutuit, 1972, Azendohsaurus madagaskarensis Flynn et al, 2010, and Shringasaurus indicus Sengupta, Ezcurra, and Bandyopadhyay, 2017. Earlier-diverging azendohsaurids now are recognized from previously known taxa (Nesbitt et al, 2021) such as Pamelaria dolichotrachela Sen, 2003, and the Malerisaurinae (e.g., Malerisaurus robinsonae Chatterjee, 1980, and Malerisaurus langstoni Chatterjee, 1986) that exhibit the tall-crowned, pointed marginal teeth found in most archosauromorphs. Unfortunately, the record of malerisaurine azendohsaurids currently is represented by fragmentary, ambiguously associated, and generally poorly preserved taxa (Nesbitt et al, 2021), which makes understanding the acquisition of azendohsaurid skeletal traits difficult to determine and difficult to compare with the morphologies of other allokotosaurs and closely related archosauromorphs such as rhynchosaurs, tanystropheids, and archosauriforms (Ezcurra, 2016;Pritchard and Sues, 2019;Pritchard et al, 2021;Spiekman et al, 2021).…”