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

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.

Figure 1

Known material referred to the baryonychines Ceratosuchops inferodios (rear) and Riparovenator milnerae (front) recovered at Chilton Chine (Isle of Wight, UK). White bones represent recovered elements. The arrangement of the elements in the caudal series is estimated; their relative position in the true series, and relationship with respect to each other (bar for those of the largely articulated mid-caudal series), are estimated. Image credit: Dan Folkes (CC-BY 4.0). Scale bar: 100 cm.

Figure 2

Locality information and stratigraphy of Chilton Chine. (a) Schematic palaeogeographic map of the Wessex and Weald sub-basins of southern England (modified from Penn et al., 2020); (b) map of the Isle Wight, highlighting the location of Chilton Chine and Wealden Group outcrops; (c) aerial photographs of Chilton Chine, highlighting the approximate position of the in situ material referred to Riparovenator milnerae (see SI) and the extensive coastal processes affecting the locality since the initial discoveries (map data: Google, Landsat/Copernicus, TerraMetrics, Maxmar Technologies); (d) schematic lithological log of the base of the exposed Wessex Fm. at Brighstone Bay (modified from Sweetman et al. 2014), highlighting approximate position of the R. milnerae in situ material. Silhouette credit: Dan Folkes (CC-BY 4.0).

Figure 3

Cranial material of Ceratosuchops inferodios. (a) Holotype skull roof fragment (IWCMS 2014.95.1), in (i) right lateral and (ii) dorsal views; (b) referred right postorbital (IWCMS 2014.95.4), in (i) dorsal, (ii) lateral and (iii) posterior views; (c) close up of holotype in situ Rpm3 (IWCMS 2014.95.5) in (i) labial and (ii) lingual views; (d) holotype basicranium (IWCMS 2014.95.3), in (i) posterior (rearticulated with the supraoccipital + left otoccipital fragment IWCMS 2014.95.2) and (ii) right lateral views; (e) holotype premaxillae (IWCMS 2014.95.5, 2021.30), in (i) ventral and (ii) right lateral views. bo basioccipital, bs basisphenoid, bpt basipterygoid process, bsr basisphenoid recess, cp cultriform process, en external naris, f frontal, fa faceting, fl fluting, fm foramen magnum, iop infraorbital process, jc jugal contact, ls laterosphenoid, lsc laterosphenoid contact, mn maxillary notch, mp maxillary process, mr median ridge, nf narial fossa, np nasal process, ns nasal sinus, ob orbital boss, oc occipital condyle, os orbitosphenoid, p parietal, pop postorbital process, pm(n) premaxillary tooth/alveolus (tooth position), prf prefrontal, pro prootic, sc sagittal crest, scr subcondylar recess, so supraoccipital, sqf squamosal contact, stf supratemporal fossa, tb tuberosity, vp ventral process of the prefrontal. Skull reconstruction credit: Dan Folkes (CC-BY 4.0). Scale bars a–b, d–e: 50 mm; c: 5 mm.

Figure 4

Cranial material of Riparovenator milnerae. (a) Close up of holotype in situ RpmVII (IWCMS 2014.95.6), in labial view; (b) referred posterior nasal fragment (IWCMS 2014.95.7) in dorsal view; (c) holotype left preorbital fragment (IWCMS 2014.96.3) in (i) lateral and (ii) anterodorsal view; (d) holotype right laterosphenoid (IWCMS 2014.96.2) in lateral view; (e) holotype skull roof and associated left laterosphenoid (IWCMS 2014.96.1) in (i) dorsal and (ii) left lateral views; (f) holotype premaxillary bodies (IWCMS 2014.95.6) in (i) left lateral and (ii) ventral views; (g) holotype basicranium (IWCMS 2020.448.1) in (i) right lateral (with fractured cultriform process IWCMS 2020.448.2), (ii) posterior and (ii) anterior views. bo basioccipital, bs basisphenoid, bpt basipterygoid process, bsr basisphenoid recess, cap capitate process of the laterosphenoid, cp cultriform process, exo exoccipital, f frontal, fl fluting, fm foramen magnum, fp frontal process, lac lacrimal, ls laterosphenoid, mn maxillary notch, mr median ridge, oc occipital condyle, os orbitosphenoid, p parietal, plp posterolateral process, pop postorbital process, pm(n) premaxillary tooth/alveolus (tooth position), prf prefrontal, pro prootic, sc sagittal crest, scr subcondylar recess, so supraoccipital, ssr subsellar recess, stf supratemporal fossa, vp ventral process of the prefrontal. Skull reconstruction credit: Dan Folkes (CC-BY 4.0). Scale bars (a): 5 mm; (b–d): 20 mm; (e–g): 50 mm.

Figure 5

Caudal material referred to Riparovenator milnerae. (a) Anterior neural arch (IWCMS 2020.447.3) in dorsal view; (b) anterior neural arch (IWCMS 2020.447.2) in left lateral view; (c) partial middle vertebra (IWCMS 2020.447.8) in (i) anterior and (ii) posterior views; (d) articulated mid-caudal series (IWCMS 2020.447.12) in (i) dorsal and (ii) left lateral views; (e) anterior centrum (IWCMS 2020.447.5) in (i) left lateral, (ii) anterior and (iii) posterior views; (f) anterior chevron (IWCMS 2020.447.20) in (i) anterior and (ii) left lateral views. as anterior spur, c centrum, ca cavity, ch chevron contact, h haemal canal, nc neural canal, ns neural spine, poz postzygapophysis, prz prezygapophysis, spof spinopostygapophyseal fossa, sprf spinoprezygapophyseal fossa, tp transverse process. Tail reconstruction credit: Dan Folkes (CC-BY 4.0). Scale bars: 50 mm.

Figure 6

Phylogenetic relationships of Spinosauridae, based on parsimony analyses. Reduced consensus tree following a posteriori pruning of rogue spinosaurid OTUs. Values at nodes indicate the Bremer support values following pruning of rogue spinosaurid OTUs as well as select fragmentary taxa (see main text). Letters represent potential placement of rogue spinosaurid OTUs: a, Irritator; b, MSNM V4047; c, “Spinosaurus B”; d, ML 1190.

Figure 7

Time-calibrated phylogenetic relationships of Spinosauridae, based on the Maximum Clade Credibility Tree inferred by the Bayesian analysis (see SI for extended figure). Numbers at nodes represent node age (top, in million years) and posterior probability values > 50% (bottom). Letters at nodes refer to the most likely ancestral area reconstructed. Geologic timescale from Walker et al. (2018). A Asia, B North America, C Europe, D Africa, E South America. Silhouette credits: Riparovenator—Dan Folkes (CC-BY 4.0); Baryonyx, Megalosaurus, Suchomimus—Scott Hartman/Phylopic (CC-BY-NC-SA 3.0); FSAC KK 11,888—Scott Hartman; Ichthyovenator—Alex Vieira (CC-BY-NC-SA 4.0).