Abstract
Background Euhelopus zdanskyi is one of relatively few sauropod taxa known from an almost complete skull and mandible. Recent phylogenetic analyses suggest that Euhelopus is a somphospondylan titanosauriform, and that it is a member of the clade (Euhelopodidae) which is the sister taxon to the hugely successful, dominantly Cretaceous sauropod group Titanosauria.Methodology/Principal FindingsThe skull elements of Euhelopus were CT scanned at Uppsala Akademiska Sjukhuset. Three-dimensional models of the elements were constructed from the DICOM data using Mimics 14.0, InVesalius 3.0, and GeoMagic Studio 2012, the skull was rearticulated in Rhinoceros 4.0, and the final version was rendered in GeoMagic Studio 2012.Conclusions/SignificanceThe fact that relatively complete sauropod skulls are so rare in the fossil record, particularly among titanosauriforms, means that the skulls that are known should be as thoroughly described and well-illustrated as possible. This contribution supplements previous descriptions of the cranial elements of Euhelopus, one of the few euhelopodid taxa for which cranial material is known, by presenting a comprehensive photographic atlas of the skull elements to facilitate a better understanding of their morphology. We describe several elements which have been overlooked in past studies of Euhelopus, and also provide as accurate a reconstruction of the skull as possible (in the absence of the braincase), the most significant components of which are the articulations of the palate and the mandible.
Highlights
Sauropod skull material is relatively rare in the fossil record
Other taxa are represented by more-or-less complete cranial remains, including Amargasaurus cazaui Salgado and Bonaparte, 1991 [34,35], Apatosaurus Marsh, 1877 [16,36,37,38,39,40], Bonitasaura salgadoi Apesteguıa, 2004 [41,42], Euhelopus zdanskyi (Wiman, 1929) Romer, 1956 [43,44,45,46], Europasaurus holgeri Sander et al, 2006 [47], Limaysaurus tessonei (Calvo and Salgado, 1995) Salgado et al, 2004 [48,49], Nigersaurus taqueti Sereno et al, 1999 [50,51,52], Patagosaurus fariasi Bonaparte, 1979 [53,54,55], Quaesitosaurus orientalis Kurzanov and Bannikov, 1983 [56], Rapetosaurus krausei Curry Rogers and Forster, 2001 [57,58] and Tazoudasaurus naimi Allain et al, 2004 [59,60,61]
As McIntosh [62] lamented over two decades ago, many otherwise well-known taxa are not represented by any cranial material at all, notably the basal sauropod Vulcanodon karibaensis Raath, 1972 [63,64], the eusauropod of debatable affinities Haplocanthosaurus Hatcher, 1903 [65,66,67,68], and the derived titanosaur Opisthocoelicaudia skarzynskii Borsuk-Białynicka, 1977 [69]
Summary
Sauropod skull material is relatively rare in the fossil record. Of the 276 named taxa, 72 (,26%) are represented by at least one non-dental skull element (Table S1); in many cases where cranial remains are present, the skull is very incompletely known (table 1 in [1]). Despite the fact that so much work on the skull of Euhelopus has already been conducted, research in the PMU collections has revealed that there are several skull elements and fragments that have not been mentioned in any previous studies; some have not even been fully prepared from the matrix in which they were preserved. Aside from the skull elements which were put on display (which were catalogued together as PMU R 233 a), each individual specimen was assigned a letter following the number
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