Abstract
Giraffidae is the only family of ruminants that is represented by two extant species; Okapia johnstoni and Giraffa camelopardalis. Of these taxa, O. johnstoni represents a typical short-necked ungulate, and G. camelopardalis exemplifies the most extreme cervical elongation seen in any ruminant. We utilize these two species to provide a comprehensive anatomic description of the cervical vertebrae. In addition, we compare the serial morphologic characteristics of the okapi and giraffe cervical vertebrae, and report on several osteologic differences seen between the two taxa. The giraffe neck appears to exhibit homogenization of C3-C7; the position of the dorsal tubercle, thickness of the cranial articular process, shape of the ventral vertebral body, and orientation of the ventral tubercle are constant throughout these vertebrae, whereas these features are serially variable in the okapi. We also report on several specializations of the giraffe C7, which we believe relates to an atypical cervico-thoracic junction, corresponding to the substantial neck lengthening. The morphologic differences exhibited between the okapi and giraffe cervical vertebrae have implications on the function of the necks relating to both fighting and feeding.
Highlights
The elongated giraffe neck clearly stands out as one of the most notable evolutionary adaptations in mammals
Two studies have focused on the posterior cervical vertebrae, which concentrated on the atypical cervico-thoracic junction and the brachial plexus [3,4]
The ruminant neck has, in addition to other minor functions, a dual role in both feeding and intra-specific male fighting, osteologic studies of cervical vertebrae to correlate to function are lacking
Summary
The elongated giraffe neck clearly stands out as one of the most notable evolutionary adaptations in mammals. While general morphologic studies have been done, the detailed anatomic features of the remarkable neck have yet to be adequately studied. The vertebral length and general osteologic features of the giraffe cervicals have been compared to other extant ungulates, including the okapi [1,2]. A comprehensive study of the functional anatomy of any ruminant neck would be complicated, as it would involve complete dissection of approximately 36 muscle types, kinematic studies, and biomechanical analyses. The osteology of the cervical vertebrae is an essential step in the evaluation of the structure and function of the neck, and facilitates future research. The giraffe and the okapi are the only extant members of a previously species-rich family with approximately 25 members [5]. An osteologic study of the giraffe and the okapi is ideal to provide a PLOS ONE | DOI:10.1371/journal.pone.0136552. An osteologic study of the giraffe and the okapi is ideal to provide a PLOS ONE | DOI:10.1371/journal.pone.0136552 August 24, 2015
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