An Unexpected Early Rhabdodontid from Europe (Lower Cretaceous of Salas de los Infantes, Burgos Province, Spain) and a Re-Examination of Basal Iguanodontian Relationships

Abstract

Disarticulated and incomplete remains from a new diminutive ornithopod are described. They come from the Cameros Basin in the north of Spain and were collected from the red clays of the Castrillo de la Reina Formation, ranging from Upper Barremian to Lower Aptian. The new ornithopod described here is slender and one of the smallest ever reported. An up-to-date phylogenetic analysis recovers this taxon as a basal iguanodontian. Its unique combination of characters makes it more derived than slender ornithopods like Hyphilophodon and Gasparinisaura, and bring very interesting insights into the basal iguanodontian phylogeny. Though possessing a minimum of three premaxillary teeth, this taxon also bears an extensor ilio-tibialis groove on the distal part of its femur. Moreover, its dentary and maxillary teeth are unique, remarkably similar to those regarded as having a “rhabdomorphan” affinity. This unknown taxon is suggested to be a stem taxon within Rhabdodontidae, a successful clade of basal iguanodonts from the Late Cretaceous of Europe. The Gondwanan ornithopods share the strongest affinities with this family, and we confirm Muttaburrasaurus as a sister taxon of the Rhabdodontidae within a newly defined clade, the Rhabdodontomorpha.

New small-bodied ornithopods (Dinosauria, Neornithischia) from the Early Cretaceous Wonthaggi Formation (Strzelecki Group) of the Australian-Antarctic rift system, with revision ofQantassaurus intrepidusRich and Vickers-Rich, 1999

“…Dataset and search methods.-The phylogenetic relationships of Australian ornithopods were assessed in TNT 1.5 (Goloboff and Catalano, 2016) using the dataset of Dieudonné et al (2016) in a substantially modified form. Two principal search methodologies, 'traditional' equal weighting (EW) and implied weighting (IW), were employed.…”

Diversity of large ornithopod dinosaurs in the upper Hauterivian-lower Barremian (Lower Cretaceous) of Teruel (Spain): a morphometric approach

“…30 in Galton [1974]; basal rhabdodontomorphans: 1.41-1.93 in MDS. VG 72 and 101 [Dieudonné et al, 2016]; Valdosaurus: 1.18 in the 6th of IWCMS 2013.175 [Barrett, 2016]) greater than those of MOR1 (L/H: 0.85-0.99). Moreover, the middle caudal centra of Hypsilophodon do not show the typical hexagonal articular faces of iguanodontians (Norman, 2004), in contrast with MOR1.…”

“…Additionally, dorsal centra in Hypsilophodon and basal rhabdodontomorphans exhibit length/height ratio (L/H) (Hypsilophodon: L/H: > 1.8 [Cobos et al, 2012]; basal rhabdodontomorphans: MDS. VG 66 and 69: 1.46-1.76 [Dieudonné et al, 2016]) greater than dorsal vertebrae of MOR2 (L/H: 1.04-1.28) and have more rounded and proportionally wider articular faces. Even though the ratio L/H of Valdosaurus certainly overlaps with those of MOR2 in the most posterior dorsal centra (Valdosaurus: IWCMS 2013.175, L/H: 1.18-1.87), they exhibit sub-circular anterior and posterior faces (Barrett, 2016).…”

“…However, attending to the diff erences stated above with other contemporaneous dinosaurs, the following combination of characters suggests an affinity with Ornithopoda: the dorsal centra of MOR2 is moderately compressed between the narrow articular faces, and, according to Knoll (2009), without pleurocoeli and with a sinuous neurocentral suture; and caudal centra of MOR1 and MOR2 are slightly compressed between the articular faces, which range from sub-quadrangular to triangular, and without transverse processes in the middle ones. Four groups of ornithopods can be distinguished in the Lower Cretaceous of the Iberian Peninsula: small basal ornithopods related to the English taxon Hypsilophodon (e.g., Sanz et al, 1983;Ruiz-Omeñaca et al, 2012), small basal iguanodontians related to the Upper Cretaceous rhabdodontids (Dieudonné et al, 2016), dryosaurids related to the English taxon Valdosaurus (e.g., Galton, 2009), and diverse large non-hadrosaurid styracosternans (e.g., Gasca et al, 2014;Gasulla et al, 2014Gasulla et al, , 2015Verdú et al, 2015;Fuentes et al, 2016), the latter being the group most frequently found in the fossil record. It should be noted that some Lower Cretaceous Iberian fossils identifi ed as basal ornithopods, indeed, might be basal ornithischians (Pereda-Suberbiola et al, 2012).…”

“…It should be noted that some Lower Cretaceous Iberian fossils identifi ed as basal ornithopods, indeed, might be basal ornithischians (Pereda-Suberbiola et al, 2012). In this context of ornithopod diversity, the vertebral centra of both MOR1 and MOR2 are much too big to belong to mature specimens of basal ornithopods such as Hypsilophodon (Galton, 1974), basal rhabdodontomorphans (Dieudonné et al, 2016) or dryosaurids such as Valdosaurus (Barrett, 2016). Additionally, dorsal centra in Hypsilophodon and basal rhabdodontomorphans exhibit length/height ratio (L/H) (Hypsilophodon: L/H: > 1.8 [Cobos et al, 2012]; basal rhabdodontomorphans: MDS.…”