The osteology, palaeoneurology and systematics of Theropod (Dinosauria) material from the Early Cretaceous of Southern England (UK), with emphasis on spinosauridae

Abstract

The Early Cretaceous deposits of the Wealden Supergroup (upper Berriasian–lower Aptian) of southern England and the Isle of Wight are an internationally important source of dinosaur material, however theropod remains are generally rare. The aim of this thesis is to describe and interpret theropod specimens – some recently discovered – from southern England and the Isle of Wight, with a particular focus on fossils belonging to Spinosauridae (Theropoda: Tetanurae). This clade of enigmatic, fish-eating theropods was mainly represented in the British fossil record by the partial skeleton of Baryonyx walkeri from the Upper Weald Clay Formation (Barremian) of Surrey, with other isolated fragments—mainly teeth—also known from Wealden Supergroup strata (Chapter 1). Osteological and phylogenetic analyses of new material from the Wessex Formation (Barremian) of the Isle of Wight suggest the presence of multiple spinosaurid lineages and an underappreciated diversity of spinosaurid taxa, including two specimens that are sufficiently diagnostic to warrant naming: Ceratosuchops inferodios and Riparovenator milnerae (Chapter 2). The latter are phylogenetically closer to the African Suchomimus tenerensis than B. walkeri, and a novel palaeobiogeographical reconstruction suggests a European (Laurasian) origin for Spinosauridae and multiple dispersal events into Gondwana. Support for a higher diversity of British spinosaurids is provided via additional lines of evidence. Cladistic and morphometric analyses of an isolated spinosaurid tooth, likely from a Valanginian unit of the older Hastings Group of East Sussex, failed to associate with Baryonyx in any data run using a large tooth-based dataset (Chapter 3). Meanwhile, the discovery of a notably large-bodied spinosaurid from the overlying Vectis Formation (upper Barremian) of the Isle of Wight also extends the temporal range of British spinosaurids, marking the youngest definitive occurrence of the clade in the British fossil record (Chapter 4). Phylogenetic analyses of this specimen were inconclusive given its fragmentary nature but the initial results argue for the presence of yet another spinosaurid lineage in the British Mesozoic. This thesis also employs microCT-based reconstruction of the endocranial cavity and associated endocast of B. walkeri and C. inferodios to shine light on the neuroanatomy and sensory capabilities of earlier branching spinosaurids (Chapter 5). Comparable to various other basal tetanurans in gross morphology, these forms possessed unexceptional hearing and olfaction, suggesting the transition from terrestrial hypercarnivorous ancestors to fish-eating “generalists” did not require substantial modification of the endocranium, or that Barremian spinosaurids already possessed the neuroanatomical adaptations required for this ecological shift. Finally, this thesis also examines rare and highly pneumatic theropod material from the Lower Greensand Group of the Isle of Wight – herein named Vectaerovenator inopinatus – whose relationships within Tetanurae could not be presently ascertained (Chapter 6). This fragmentary specimen is one of Britain’s youngest non-avian theropods and the first named taxon from the Aptian of Europe, providing valuable data from a poorly sampled period of European Mesozoic. In totality, this work substantially contributes to the diversity and relationships of the theropod fossil record from Britain, provides the first endocranial studies of baryonychine grade spinosaurids, and helps refine the understanding of spinosaurid palaeoecology (Chapter 7).

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ORCID for Christopher Tijani Barker: orcid.org/0000-0001-8792-3307

ORCID for Neil Gostling: orcid.org/0000-0002-5960-7769

ORCID for Philipp Schneider: orcid.org/0000-0001-7499-3576

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