Dinosaur micro-remains from the Middle Jurassic of Britain

Wills, Simon (2023) Dinosaur micro-remains from the Middle Jurassic of Britain. PhD thesis, Birkbeck, University of London.

Abstract

In the Middle Jurassic, Great Britain was situated at ~30° north in an area of shallow seas with surrounding low-lying landmasses. Fluctuations in relative sea level resulted in emergent areas preserving snapshots of the terrestrial fauna in microvertebrate sites throughout southern England. Analysis of the dinosaur material, mostly isolated teeth, has resulted in a much more granular view of the taxa present including clades previously unknown or unconfirmed from this period. I developed machine learning techniques, which combined with morphological-based approaches confirms the presence of at least three maniraptoran taxa in the assemblage: three dromaeosaur morphotypes; a troodontid; and a therizinosaur. These results provide the first quantitative support for the presence of maniraptoran theropods, including the oldest occurrences of troodontids and therizinosaurs worldwide, in the Middle Jurassic and are consistent with predictions made by phylogenetic analyses. There are at least six ornithischian taxa in the assemblage; a distinctive highly-ridged morphotype that cannot be referred with certainty to any known ornithischian taxa and therefore represents a new taxon; a number of small teeth with denticles restricted to the upper third of the crown which represent a hitherto unknown occurrence of heterodontosaurids in the Middle Jurassic of the UK; at least one morphotype of a basal thyreophoran; an indeterminate thyreophoran; a stegosaur, which represents one of the oldest stegosaurs worldwide; and a number of ankylosaur morphotypes which make up the vast majority of the isolated ornithischian teeth seen from these sites. The application of machine learning, when combined with traditional morphological comparisons provides a powerful tool for the qualitative assessment of isolated teeth. This analysis increases the known diversity of Middle Jurassic dinosaur taxa in the UK and the confirmation of early maniraptorans, heterodontosaurids and stegosaurs highlights the importance of incorporating microvertebrate remains into faunal and evolutionary analyses.

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