Unrelated ornithopods with similar tooth morphology in the vicinity of Salas de los Infantes (Burgos Province, Spain): an intriguing case-study

Abstract

The Lower Cretaceous of the Salas de los Infantes locality (Burgos Province, Spain) is extremely rich in monospecific ornithopod sites, each comprising a variety of cranial and postcranial remains. Among these, Vegagete and El Penascal-1 lie in very close vicinity within the Upper Barremian–Lower Aptian Castrillo de la Reina Formation. In addition to other skeletal elements, these sites yield surprisingly similar teeth, which was viewed as an argument to regard the ornithopods from both sites as akin to each other. However, claiming phylogenetic affinity based on the sole tooth similarity is not satisfactory, as tooth similarity might also result from convergent evolution. This article tackles the question of the apparent similarity in tooth morphology between the ornithopods of both sites. Is it a result of convergent evolution or was it acquired from a close common ancestor? What are the ecological implications of their tooth morphologies and dental wear in terms of dietary niche partitioning? We discuss on the taxonomic relatedness of the ornithopods of both sites based on a detailed comparison of their teeth. We test for the morphometric differences and similarities between the tooth crowns of both assemblages through successive Student t tests and one Multivariate Analysis of Variance (MAnOVa). Our conclusion is that although they bear similar teeth, the Vegagete and El Penascal-1 ornithopods belong to different ornithopod lineages. The Student t tests show that the mesiodistal sharpness index is significantly higher in the Vegagete ornithopod. This is consistent with the formerly inferred kinship of this taxon with the family Rhabdodontidae, and probably indicates that the ancestors of this lineage became adapted to eating tough plant material since the Early Cretaceous.