Abstract
Spinosaurids are among the most distinctive and yet poorly-known of large-bodied theropod dinosaurs, a situation exacerbated by their mostly fragmentary fossil record and competing views regarding their palaeobiology. Here, we report two new Early Cretaceous spinosaurid specimens from the Wessex Formation (Barremian) of the Isle of Wight. Large-scale phylogenetic analyses using parsimony and Bayesian techniques recover the pair in a new clade within Baryonychinae that also includes the hypodigm of the African spinosaurid Suchomimus. Both specimens represent distinct and novel taxa, herein named Ceratosuchops inferodios gen. et sp. nov. and Riparovenator milnerae gen. et sp. nov. A palaeogeographic reconstruction suggests a European origin for Spinosauridae, with at least two dispersal events into Africa. These new finds provide welcome information on poorly sampled areas of spinosaurid anatomy, suggest that sympatry was present and potentially common in baryonychines and spinosaurids as a whole, and contribute to updated palaeobiogeographic reconstructions for the clade.
Highlights
Spinosaurids are among the most distinctive, unusual and controversial of theropods; they are characterised by an elongate, laterally compressed rostrum, sub-conical dentition and, in a subset of taxa, a dorsal sail formed by elongate neural spines
Ceratosuchops inferodios and Riparovenator milnerae represent new Wealden Group theropod taxa, differing from the other broadly contemporaneous spinosaurid Baryonyx walkeri in numerous anatomical features
We are cognisant that some of the differences we report for our two new baryonychine taxa are associated with individual and/or ontogenetic variation in better-sampled theropods (Appendix 1); intraspecific variation is seen to increase throughout the extreme ontogenetic series of the tyrannosaurid Tyrannosaurus[50], for instance
Summary
Spinosaurids are among the most distinctive, unusual and controversial of theropods; they are characterised by an elongate, laterally compressed rostrum, sub-conical dentition and, in a subset of taxa, a dorsal sail formed by elongate neural spines. Their unusual cranial (and in derived forms, postcranial) morphology is atypical of nonavian theropods, and multiple lines of evidence point to an ability to exploit semi-aquatic n iches[1,2,3,4,5,6,7,8]. Teeth referred to the nomen dubium “Suchosaurus cultridens”, from the Valanginian Grinstead Clay Formation of West Sussex, have been attributed to Baryonyx[33,34], other work has favoured an indeterminate baryonychine position[30,35,36]
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