A hidden diversity of ornithischian dinosaurs: U.K. Middle Jurassic microvertebrate faunas shed light on a poorly represented period

ABSTRACT

Current research suggests that ornithischians originated in the Middle–Late Triassic and achieved a global distribution by the Early Jurassic, but the Middle Jurassic was a pivotal period in which the clade underwent rapid diversification and radiation. However, Middle Jurassic ornithischian fossils are rare, with few named taxa and numerous occurrences of isolated teeth with disputed identifications. Here, we apply detailed morphological comparisons to a suite of isolated ornithischian teeth from Bathonian microvertebrate sites in the U.K., to assess their taxonomic affinities. These reveal a hitherto unknown, highly diverse ornithischian fauna that significantly increases the known diversity of ornithischians from this time period in the U.K. Comparisons indicate the presence of six ornithischian morphotypes: an indeterminate ornithischian, a heterodontosaurid, two indeterminate thyreophorans, a stegosaur, and an ankylosaur. These results confirm the predictions made by phylogenetic studies that Ornithischia rapidly diversified in the Middle Jurassic, fill in temporal gaps within lineages, and also include recognition of one of the oldest global occurrences of stegosaurs. In addition, the mixture of non-eurypodan and eurypodan morphotypes identified suggests that not only did non-eurypodans survive until at least the Middle Jurassic but they also co-existed with early eurypodans.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

ACKNOWLEDGMENTS

We would like to thank M. McKenna who provided access to Woodeaton Quarry, Breedon Aggregates for providing access to Hornsleasow Quarry and permission to collect additional samples, Susan Evans for access to previously collected material from Kirtlington Quarry and W. Cliff, and the Museum of Gloucester for access to the Hornsleasow material. We also thank V. Fernandez and Brett Clarke at the Imaging and Analysis Centre, Natural History Museum, London, for CT access and scanning. Susannah Maidment and Andrew Heckert provided useful discussions. We are grateful to the field crews at Woodeaton and Hornsleasow quarries: D. Ward, E. Bernard, P. Brewer, M. Richter, T. Ewin, J. Párraga, M. Graham, A. Lister, S. Stukins, A. Gale, Z. Hughes, A. Ward, A. Ward, M. Smith, K. Banton, C. Bullar, R. Schofield, and J. Bonsor. Additional thanks go to the reviewers L. Czepiński and M. Becerra for their useful comments that helped to improve this contribution.

AUTHOR CONTRIBUTIONS

Conceptualization SW, CJU, PMB; Data Curation SW; Formal Analysis SW; Funding Acquisition SW, CJU, PMB; Investigation SW; Methodology SW; Project Administration SW, CJU, PMB; Resources SW, CJU, PMB; Software SW; Supervision CJU, PMB; Validation SW, CJU, PMB; Visualization SW; Writing—Original Draft Preparation SW; Writing—Review & Editing SW, CJU, PMB.

DATA AVAILABILITY STATEMENT

Image data for this study are available in MorphoSource (https://www.morphosource.com/projects/000556869)