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Orofacial morphology and feeding behaviour of the dugong, Amazonian, West African and Antillean manatees (Mammalia: Sirenia): functional morphology of the muscular-vibrissal complex

Published online by Cambridge University Press:  10 March 2003

Christopher D. Marshall
Affiliation:
Department of Marine Biology, Texas A&M University at Galveston, Galveston, TX 77551, U.S.A.
Hiroshi Maeda
Affiliation:
Toba Aquarium, Toba 3-3-6, Toba City, Mie Prefecture 517, Japan
Matsumitsu Iwata
Affiliation:
Yomiuriland Marine Aquarium, 3294 Yanokuchi, Inagi City, Tokyo 206, Japan
Masami Furuta
Affiliation:
Toba Aquarium, Toba 3-3-6, Toba City, Mie Prefecture 517, Japan
Shiro Asano
Affiliation:
Toba Aquarium, Toba 3-3-6, Toba City, Mie Prefecture 517, Japan
Fernando Rosas
Affiliation:
Instituto Nacional de Pesquisas da Amazonia (INPA), Alameda Cosme Ferreira 1767 Manaus, Amazonas, Brazil
Roger L. Reep
Affiliation:
Department of Physiological Sciences, University of Florida, Gainesville, FL 32610-0144, U.S.A.
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Abstract

The external orofacial morphology, perioral bristle distribution and feeding behaviour of Dugong dugon, Trichechus inunguis, T. senegalensis and T. manatus are described. Despite their differing orofacial morphology, dugongs and trichechids possess six similar regions: the oral disk, orofacial ridge, supradisk, chin and upper and lower bristle (modified vibrissae) pads. All living sirenians possess six discrete fields of bristles: four on the upper lip (U1, U2, U3, and U4) and two on the lower lip (L1 and L2). The distribution of these fields is similar among all living sirenians with the exception of the U1 bristle fields in dugongs. Perioral bristle field boundaries are distinguished by distinct changes in their length-to-diameter ratios. Both dugongs and trichechids possess bristle-like hairs covering the oral disk, which possess length-to-diameter ratios intermediate between perioral bristles and postcranial hairs. Sirenians use elaborated facial musculature in conjunction with perioral bristles to acquire, manipulate and ingest aquatic vegetation. The U2 and L1 fields are the primary bristles used to ingest vegetation. The use of the L1 bristle fields is similar among all living sirenians. However, dugongs and trichechids are divergent in their use of the U1 and U2 bristle fields. Dugongs use the U2 bristles fields in a medial-to-lateral motion, while all trichechids use the U2 bristles in a prehensile, lateral-to-medial, grasping motion. These divergent behaviours presumably allow dugongs to exploit benthic foraging (i.e. consumption of rhizomes) to a greater degree than trichechids. Functional hypotheses of rhizome excavation are presented for both dugongs and trichechids.

Type
Research Article
Copyright
2003 The Zoological Society of London

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