A taxonomic revision and cranial description of Terrestrisuchus gracilis (Archosauria, Crocodylomorpha) from the Late Triassic of Pant-y-ffynnon Quarry (southern Wales)

Stephan N.F. Spiekman*, Vincent Fernandez, Richard Butler, Kathleen N. Dollman, Susannah Maidment

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Non-crocodyliform crocodylomorphs, formerly referred to the informal group “Sphenosuchia”, are the earliest known crocodylomorph precursors of extant crocodylians. Therefore, they are crucial for our understanding of early crocodylian evolution and the origin of typical crocodylian characteristics, such as the formation of a secondary palate, complex cranial pneumaticity, and a reinforced braincase. Terrestrisuchus gracilis, known from the Late Triassic fissure fill deposits of Pant-y-ffynnon in southern Wales, is represented by almost 200 specimens, comprising articulated, partially associated, and isolated remains. In this contribution, we provide a taxonomic revision of Terrestrisuchus gracilis and redescribe its cranial anatomy in detail, based in part on novel μCT data. The posterior skull region is extensively pneumatised as indicated, among other features, by large pre- and postcarotid recesses on the parabasisphenoid and a large pneumatic cavity within the articular of the mandible. In contrast, the quadrate only forms a small, unfused contact with the prootic, suggesting that complex pneumatization of the postorbital region predated the coossification of the quadrate and braincase in Crocodylomorpha. Terrestrisuchus gracilis preserves an ossified basihyal, which represents the first occurrence of this bone among non-avemetarsalian archosaurs. Finally, we show that Terrestrisuchus gracilis was likely cathemeral (i.e. active in a range of light levels), based on a phylogenetic flexible discriminant analysis (pFDA) of the relative dimensions of the sclerotic ring and orbit.
Original languageEnglish
Article numbere1534
Number of pages72
JournalPapers in Palaeontology
Volume9
Issue number6
Publication statusPublished - 27 Nov 2023

Bibliographical note

Acknowledgments:
The morphological description of Terrestrisuchus gracilis was aided by the unpublished PhD thesis of Peter Crush, who described the crocodylomorph material from Pant-y-Ffynnon in excellent detail. Additional information was also derived from the unpublished PhD thesis of Rachael Allen, who provided additional observations on the material. David Gower (NHMUK) is thanked for insightful discussions, and Roger Benson kindly provided the R script used for part of the analyses of the sclerotic ring. We thank Lu Allington-Jones (NHMUK) for conservation work and Kevin Webb and Aimee McArdle (NHMUK) for specimen photography. We thank reviewers Alexander Ruebenstahl and Juan Martín Leardi, as well as editor Philip Mannion for their constructive suggestions that helped improve the manuscript. Stephan Spiekman was funded by a Swiss National Science Foundation Early Postdoc Mobility Fellowship (P2ZHP2_195162 to SNFS) and the Deutsche Forschungsgemeinschaft (grant no. SCHO 791/7-1 to Rainer Schoch, SMNS). Open Access funding enabled and organized by Projekt DEAL.

Keywords

  • Terrestrisuchus
  • Crocodylomorpha
  • Triassic
  • CT scanning
  • cranial osteology
  • braincase pneumaticity

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