Cranial anatomy of the Late Jurassic dwarf sauropod Europasaurus holgeri (Dinosauria, Camarasauromorpha): ontogenetic changes and size dimorphism

MARPMANN, SEBASTIAN; CARBALLIDO J. L.; SANDER P. M.; KNÖTSCHKE N.

JOURNAL OF SYSTEMATIC PALAEONTOLOGY

CAMBRIDGE UNIV PRESS

Lugar: Cambridge; Año: 2015 vol. 13 p. 221 - 263

1477-2019

Sauropods were the most successful herbivorous group of dinosaurs during the Mesozoic era. Despite their supremacy as reflected in the fossil record, sauropod skulls are very rare and current knowledge of skull anatomy is based on just a few taxa. Juvenile skull bones are even rarer than adult skulls; thus, our understanding of their morphology and ontogenetic changes is limited. The recent discovery of several adult and juvenile specimens of a Late Jurassic taxon from Germany, Europasaurus holgeri, extends our knowledge of sauropod skull anatomy. A total of 123 skull bones, representing at least 14 skulls, were examined, described and compared to other taxa. The skull material includes several individuals of various ontogenetic stages. Because size alone is not sufficient to determine the morphological ontogenetic stage (MOS), sizeindependent characters were used to stage the bone elements. Detailed studies of the skull bones proved that the material represents two morphotypes, independent of ontogenetic stage. Since the original description of Europasaurus, new skull material has been found, and an updated skull reconstruction of an adult individual is presented here. All the autapomorphic characters of Europasaurus recognized in the skull (i.e. anteroposteriorly long and lateromedially narrow frontal; presence of postparietal fenestra; large participation of the jugal to the ventral rim of the skull and the orbit; presence of a postparietal foramen and single optic foramen) are plesiomorphic characters of basal sauropodomorphs and/ or present in embryos and juvenile sauropods. Therefore, we consider that in Europasaurus these characters evolved through paedomorphosis, which resulted in the dwarf condition of this taxon.