Science 26 September 2014:
Vol. 345 no. 6204 pp. 1613-1616

Semiaquatic adaptations in a giant predatory dinosaur

Nizar Ibrahim, Paul C. Sereno, Cristiano Dal Sasso, Simone Maganuco, Matteo Fabbri, David M. Martill, Samir Zouhri, Nathan Myhrvold, Dawid A. Iurino | 1 Comments

New fossils of the sail-finned predatory dinosaur Spinosaurus reveal that it lived in and near water.

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Ibrahim et al. have taken an assortment of incomplete spinosaur remains found over an enormous territory of North Africa spanning 3000 km, found in sediments whose exact temporal correspondence is not certain, and presumed that they represent one genus and species. This despite the specimens being limited in overlapping comparative material, being of different ontogenetic stages, and there being some uncertainty concerning the individuality of some specimens -- a large gap in the vertebrae of juvenile/s FSAC-KK 11888 between the mid dorsals and sacrals makes the conclusion it is one individual a matter of opinion. The unusual length of the dorsals relative to the pelvic sacral/pelvic/hindlimb elements in 11888 is suspicious, and should not be presumed real unless it is present in a more complete and articulated specimen, preferably adult. An attempt by this experienced paleoillustrator to use the array of specimens to produce a reliably proportioned composite technical skeleton of Spinosaurus aegypticus was abandoned due to these and other issues – it is my experience that composite skeletons of novel taxa constructed under these circumstances later often prove substantially errant when more complete specimens are obtained. The actual skeletal proportions of Spinosaurus therefore remain uncertain, and the extreme shortness of the hindlimbs restored by Ibrahim et al. is questionable, although the possibility that the genus had exceptionally abbreviated legs cannot be ruled out. Even more open to challenge is the near equality of the length of the arms relative to the legs, and the idea that the theropodian arms were used in locomotion. Attempts to calculate the absolute center of mass of extinct dinosaurs even when the specimen is a complete individual is always debatable, and doing so with a problematically proportioned composite based on so many individuals of differing ages from so many places risks producing misleading results. Also doubtful is the designation of FSAC-KK 11888 as the neotype of S. aegypticus. Minimal overlapping material, differing ontogenetic stages, possible time separation, and the 3000 km separation make it very possible that 11888 and the destroyed holotype represent different taxa. The possibility that 11888 is more than one individual is another difficulty in this regard. Ibrahim et al. appear to have over interpreted the available fossils.

Submitted on Mon, 12/01/2014 - 13:14