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.
Highlights
Seeley [1] was the first to recognize two orders within Dinosauria: Saurischia and Ornithischia
Specimen MDS-VG,57 is a centrum that belongs to a mid-series dorsal vertebra from the smallest individual of the sample, i.e. a juvenile individual
In Muttaburrasaurus, Bartholomai and Molnar [50] mention that the anterior surface of the humerus was nearly flat proximally; based on the illustrations, we do not consider it flat enough to code this character as present. This character appears to exclude Muttaburrasaurus (184 (0)) [47] from the Rhabdodontidae (184 (1)).On the other hand, we found that the bigger Laurasian iguanodonts (e.g. Dryosaurus altus, Dysalotosaurus lettowvorbecki, Tenontosaurus tilletti [5, 87]) and other primitive ornithopods (e.g. Hypsilophodon foxii [28]) contrast in having a much deeper and irregular bicipital sulcus
Summary
Seeley [1] was the first to recognize two orders within Dinosauria: Saurischia and Ornithischia. Ornithischia is recognized by a typically posteriorly oriented pubis. Within Ornithischia, Romer [2] considered Ornithopoda as a suborder that includes all the relatively unspecialized, PLOS ONE | DOI:10.1371/journal.pone.0156251. Discovering of the Earliest European Rhabdodontid, and the Origins of the Rhabdodontidae Within Ornithischia, Romer [2] considered Ornithopoda as a suborder that includes all the relatively unspecialized, PLOS ONE | DOI:10.1371/journal.pone.0156251 June 22, 2016
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