Pushing the boundary? Testing the functional elongation hypothesis of the giraffe's neck

Mueller, Marilena A.; Merten, Luisa J. F.; Boehmer, Christine und Nyakatura, John A. (2021): Pushing the boundary? Testing the functional elongation hypothesis of the giraffe's neck. In: Evolution, Bd. 75, Nr. 3: S. 641-655

Abstract

Although giraffes maintain the usual mammalian cervical number of seven vertebrae, their first thoracic vertebra (T1) exhibits aberrant anatomy and has been hypothesized to functionally elongate the neck. We test this functional elongation hypothesis by combining phylogenetically informed analyses of neck length, three-dimensional (3D) vertebral shape, and of the functional significance of shape differences across a broad sample of ruminants and camelids. Digital bone models of the cervicothoracic transition were subjected to 3D geometric morphometric analysis revealing how the shape of the seventh cervical (C7) has converged in several long-necked species. However, we find a unique cervicalization of the giraffe's T1. In contrast, we demonstrate a thoracalization of C7 for the European bison. Other giraffids (okapi and extinct Sivatherium) did not exhibit cervicalized T1 morphology. Quantitative range of motion (ROM) analysis at the cervicothoracic transition in ruminants and camelids confirms the functional elongation hypothesis for the giraffe in terms of increased mobility, especially with regard to dorsoventral flexion/extension. Additionally, other factors related to the unique morphology of the giraffe's cervicothoracic transition such as neck posture and intervertebral stability are discussed and should be considered in future studies of giraffe neck evolution.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 0014-3820
• Sprache: Englisch