New spinosaurids from the Wessex Formation (Early Cretaceous, UK) and the European origins of Spinosauridae

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.

1 0 n/a 0 Oval scar excavation apomorphic for Ceratosuchopsini (see main text; row 37), Ceratosuchops could simply represent individual variation of this trait (albeit arguably extreme in terms of morphological difference).
1 0 0 0 Ambiguous if individual variability affecting pneumatic features bordering it; Web becomes thicker during Tyrannosaurus ontogeny (Carr, 2020: ch 1050 -blade-like in young adults, long and convex in adults), although Wealden Supergroup spinosaurids do not display blade-like morphology.
1 0* 0* ? *Potentially ambiguous as the right otoccipitals in Baryonyx and Riparovenator are missing lateral part of the process; unable to test for intra-individual variation in facet shape.  (Carr, 1999: 507).
? 0 1 ? Not unique as Vallibonavenatrix is also scored the same (taxon recovered as baryonychine in parsimony analysis.); Comparisons potentially affected by non-overlapping elements.

Further Comparisons: Characters shared between both Wessex Fm. specimens but not other baryonychines
Ceratosuchops + Riparovenator mimus 1 1 0 1 Cranial facets may be generally variable (Molnar, 1990), deeper facets affect larger specimens; Ontogeny/individual variation affects postorbital frontal process shape (and thus frontal postorbital facet shape, which accomodates the process) in Tyrannosaurus (Carr, 2020: Ch 68, 69 -some young adults and adults display the immature "shorter" state re: facet height and length).
45 Parietal, posterior rise of the nuchal crest in lateral view (angle measured in lateral view with the skull roof held horizontally; the vertex of the angle is located on the capitate process of the laterosphenoid (or preserved equvialent); the first ray projects to the dorsal nuchal crest; the second ray projects posteriorly): ≥ (0), or < (1) 45º.
46 Orbital margin, exposure of the orbital fossae in lateral view: orbital fossae visible (0); dorsal portion of orbital fossae partially obscured by overhang of the orbital rim (1). 52 Supraoccipital, dorsal process, width (measured between the foramina for the middle cerebral vein) relative to height (measured from a middle cerebral vein foramen to the tip of the dorsal process): width more than (0) or less than (1) 2/3 process height.