Why giraffes have such short necks

28th September 2010

Michael P. Taylor1 and Mathew J. Wedel2
1Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom. E-mail: <dino@miketaylor.org.uk>
2College of Osteopathic Medicine of the Pacific and College of Podiatric Medicine, Western University of Health Sciences, 309 E. Second Street, Pomona, California 91766-1854. E-mail: <mathew.wedel@gmail.com>

The necks of sauropod dinosaurs were by far the longest of any animals, exceeding 15m. Four clades with very different cervical morphologies (mamenchisaurids, diplodocids, brachiosaurids, and titanosaurians) evolved 10m necks. By contrast, the neck of the giraffe, the longest of any extant animal, reaches only 2.4m. Those of theropods and pterosaurs attained at most 3m. (Even among aquatic animals, the record is only 7m for elasmosaurs.) Four factors contributed to sauropod neck length: the sheer size of the animals, their distinctive vertebral architecture, air-sacs, and heads that merely gathered food without processing it. Cervical vertebral innovations included: extreme pneumatisation, which lightened the neck and increased bending resistance; elongate cervical ribs, which allowed hypaxial muscles to shift posteriorly; and, in several clades, bifid neural spines, which aided stability by shifting epaxial tension elements laterally. Bifid cervicals evolved at least four times among sauropods and were never secondarily lost; they are otherwise found only in Rhea. However, other aspects of sauropod cervical anatomy remain puzzling: low neural spines reduced the moment arm of epaxial tension members; ventrally displaced cervical ribs increased bulk; and epipophyses were not posteriorly elongated. These apparent flaws suggest our understanding of sauropod neck mechanics remains incomplete.


This abstract is also available on the SVPCA web-site at http://svpca.org/general/pages/abstractPage.php?i=1481&r=talksAndPosters.php&y=2010

The entire abstracts volume for SVPCA 2010 can be downloaded from http://svpca.org/years/2010_cambridge/nps814B.tmp.pdf [Local copy]

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