Revision ofErpetosuchus(Archosauria: Pseudosuchia) and new erpetosuchid material from the Late Triassic ‘Elgin Reptile’ fauna based on μCT scanning techniques

Abstract

The Late Triassic fauna of the Lossiemouth Sandstone Formation (LSF) from the Elgin area, Scotland, has been pivotal in expanding our understanding of Triassic terrestrial tetrapods. Frustratingly, due to their odd preservation, interpretations of the Elgin Triassic specimens have relied on destructive moulding techniques, which only provide incomplete, and potentially distorted, information. Here, we show that micro-computed tomography (μCT) could revitalise the study of this important assemblage. We describe a long-neglected specimen that was originally identified as a pseudosuchian archosaur, Ornithosuchus woodwardi. μCT scans revealed dozens of bones belonging to at least two taxa: a small-bodied pseudosuchian and a specimen of the procolophonid Leptopleuron lacertinum. The pseudosuchian skeleton possesses a combination of characters that are unique to the clade Erpetosuchidae. As a basis for investigating the phylogenetic relationships of this new specimen, we reviewed the anatomy, taxonomy and systematics of other erpetosuchid specimens from the LSF (all previously referred to Erpetosuchus). Unfortunately, due to the differing representation of the skeleton in the available Erpetosuchus specimens, we cannot determine whether the erpetosuchid specimen we describe here belongs to Erpetosuchus granti (to which we show it is closely related) or if it represents a distinct new taxon. Nevertheless, our results shed light on rarely preserved details of erpetosuchid anatomy. Finally, the unanticipated new information extracted from both previously studied and neglected specimens suggests that fossil remains may be much more widely distributed in the Elgin quarries than previously recognised, and that the richness of the LSF might have been underestimated.

Scleromochlus and the early evolution of Pterosauromorpha

“…This additional step was necessary to: capture the specimens in their entirety in a single scan; to minimise the risk of misidentification of individual elements that have been broken into separate sections and preserved in different parts of the original articulated blocks (e.g. the humerus in NUMUK PV R3556); and to improve measurement accuracy 14 . The μCT data were processed and segmented using Mimics Research v22.0 47 .…”

“…Previous anatomical studies of Scleromochlus have relied primarily on casts of natural moulds of the skeletons. While such casts were long necessary, their ability to capture tiny, but crucial, anatomical details has been questioned and the reliability of the interpretations based upon them are debated [4][5]9,[13][14] .…”

Femoral specializations to locomotor habits in early archosauriforms

“…A phylogeny was constructed following the dataset of Nesbitt (2011) and recent iterations (Butler et al, 2014;Ezcurra et al, 2020) using Mesquite software v. 3.61 (Maddison & Maddison, 2019) with all branch lengths set to 1. The phylogenetic position of Parringtonia within Archosauria remains poorly understood (Foffa et al, 2020;Nesbitt & Butler, 2013). However, we followed the finding of Nesbitt et al (2018) that Parringtonia was an early diverging suchian based on its braincase anatomy.…”

Skull osteology of Aetosauroides scagliai Casamiquela, 1960 (Archosauria: Aetosauria) from the Late Triassic of Brazil: New insights into the paleobiology of aetosaurs

“…Another shared feature between MCN-PV 2347 and UFSM 11505 is the presence of a marked ridge that runs longitudinally (confluent with the maxilla), dividing the main body of the jugal into laterodorsal and lateroventral faces (Figures 4 and 7A: r). This ridge is also present in phytosaurs (Stocker et al, 2017), gracilisuchids (e.g., MCZ 4117), paracrocodylomorphs (e.g., Prestosuchus chiniquensis Huene 1938;Mastrantonio et al, 2019; Dromicosuchus grallator Sues et al, 2003), erpetosuchids (e.g., Maisch et al, 2013;Ezcurra et al, 2017;Lacerda et al, 2018;Foffa et al, 2020), Acaenasuchus geoffroyi (see Marsh et al, 2020), and in several aetosaurs, such as Longosuchus meadei (TMM 31185-84), Desmatosuchus spurensis (UMMP V7476), Aetosaurus ferratus (SMNS 5770 S-16), Stenomyti huangae (according to Small and Martz, 2013), Coahomasuchus chathamensis (NCSM 23618), and Coahomasuchus kahleorum Heckert and Lucas, 1999 (NMMNH P-18496). This ridge is not prominent in some aetosaurs, such as Paratypothorax andressorum (SMNS 19003;Schoch and Desojo, 2016) and Typothorax coccinarum (PEFO 38001; Reyes et al, 2021), and is absent in ornithosuchids (von Baczko and Desojo, 2016).…”

“…However, the relationship between this Revueltosaurus-aetosaur clade and others on the crocodilian stem remains poorly resolved. Early cladistic studies tended to recover aetosaurs as closely related to Crocodylomorpha (Parrish, 1994;Gower and Walker, 1996;Brusatte et al, 2010), but more recent analyses generally recover this clade either near the base of Pseudosuchia (Nesbitt, 2011;Butler et al, 2014;Ezcurra, 2016;Lacerda et al, 2018;Desojo et al, 2020b;Foffa et al, 2020) or as part of a larger clade with the enigmatic erpetosuchids (Ezcurra et al, 2017;Nesbitt et al, 2017;Müller et al, 2020;Marsh et al, 2020).…”