Comments about the cervical vertebrae referred to the african theropods Carcharodontosaurus and Sigilmassasaurus

CANALE, JUAN IGNACIO; NOVAS, FERNANDO EMILIO; HALUZA, ALEJANDRO

Neuquén

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

The theropod record from the Cenomanian of northern Africa is still poorly known. It includes some isolated and peculiar neck vertebrae belonging to a large and bulky dinosaur, the phylogenetic affinities of which remain highly debated. Originally, these cervicals were described as “Spinosaurus B” by Stromer (1934), but more recently they were considered by Russell (1996) as being sufficiently different from other theropods to justify the erection of a new taxon, Sigilmassasaurus brevicollis. These cervicals distinguish for the following combination of features: 1) broad, low, and strongly opisthocoelous centra; 2) caudal articular surface of centrum reniform in outline; 3) prominent keel on ventral surface of centrum; 4) neural spine weakly developed; 5) epipophyses and prezygoepipophyseal ridges absent; 6) presence of a single pleurocoel located above the parapophysis; 7) internal osseous tissue of the camerate type. Sereno et al. (1996) and Brussatte and Sereno (2007) interpreted these cervicals as belonging to Carcharodontosaurus saharicus, proposing S. brevicollis as a subjective junior synonym of C. saharicus. However, none of the Sigilmassasaurus-kind of cervicals were found in association with cranial materials of Carcharodontosaurus. Moreover, as it was noted by Novas et al. (2005), these peculiar cervicals look sharply different from these of the better-known Patagonian carcharodontosaurids (Giganotosaurus, Tyrannotitan, and Mapusaurus), which bear centra dorsoventrally deep, ventral keel slightly developed (if present), epipophyses strongly developed, presence of a sharp prezygoepipophyseal ridge, and double pleurocoels. Also, in Giganotosaurus and Tyrannotitan, at least, the internal bone tissue is of camellate type. In sum, we interpret that the Sigilmassasaurus-kind of cervicals do not correspond to C. saharicus, either to Carcharodontosauridae. Interestingly, the Sigilmassasaurus-kind of cervicals closely resemble that of the big ornithopod Iguanodon, sharing at least characters 1, 2, 3, 4, 5, and 6 listed above. It can not be dissmissed that Sigilmassasaurus is, in fact an ornithischian rather a theropod dinosaur, a possibility that needs to be analysed in more detail.