The myology of the Amazonian Manatee, Trichechus inunguis (Natterer) (Mammalia: Sirenia)

Abstract

The muscles of the Amazonian manatee are described and compared with those of other manatees and the dugong. Maps of muscle attachments and data on weights of muscles are included. The manatee species differ in the forms of the mm. rectus capitis lateralis and biceps brachii. The mechanisms of protrusion of upper-lip bristles and opening of the nostrils are described. The jaw apparatus is uniquely specialized, with a very large temporalis muscle constituting more than half the adductor muscle mass, and development of a joint between the pterygoid process and the mandible which probably braces the mandible during transverse chewing. The center of mandibular rotation in transverse chewing probably lies posteromedial to the pterygoid process on the active side: the contralateral temporalis is dominant in transverse chewing. Trichechus inunguis is more specialized for surface-feeding and for swimming than T. manotus.

Character evolution in the orbital region of the Afrotheria

“…In most cases between 10 and 50 cranial specimens were examined per family, but only two elephant skulls and two manatees were available for inspection. In these two cases, information on orbital structure was also gathered from previously published literature (Elephantidae: Gregory, 1903; Van der Merwe, Bezuidenhout & Seegers, 1995; Trichechidae: Petit, 1958; Domning, 1978). Details of the specimens examined are shown in Supplementary Material Appendix S1.…”

CT scans and 3D reconstructions of Florida manatee (Trichechus manatus latirostris) heads and ear bones

“…The purpose of this study was to verify previous observations (Henson, 1974;Domning, 1978;Fleischer, 1978;Fischer, 1988;Ketten et al, 1992), to resolve conflicting information (e.g., structure of external auditory meatus and connection between the incus and periotic bones), and to present additional morphometric data on the auditory anatomy and density data on the soft tissue and bones of the head. The research was carried out using a combination of three-dimensional reconstructions created from computerized tomography (CT) data on fresh (thawed) manatee heads as well as direct measurements and anatomical descriptions from dissected heads and ear bones.…”

“…The dorsocaudal portion of the tympanic bone is ossified with a ventrolateral process of the periotic. The ventral end of this process is the proximal attachment site for the dorsal, cartilaginous portion (stylohyal) of the hyoid complex (Domning, 1978). The epihyoid extends rostroventrally from the stylohyal and is attached to the basihyoid by cartilage and soft tissue (Domning, 1978).…”

Historical Perspectives: The Early Years of the Amazonian Manatee Project at INPA, Manaus, Brazil

“…My dissections would also help clean out our freezers and reduce the number of half-thawed carcasses that would have to be hastily moved the next time one broke down! In the end, this study not only described the manatee's entire myology but also revealed that manatees have a unique jaw apparatus dominated (unlike dugongs and most other herbivores) by the temporalis muscle, with an extra jaw joint between the pterygoid process and the mandible (Domning, 1978b).…”

“…Simultaneously, there came another piece of welcome news: the Brazilian Army (!) had agreed to allow INPA to publish my manatee muscle monograph in English rather than Portuguese (Domning, 1978b). This I owed to Dr. Kerr, who had convinced the military authorities running the government that my research was of so little significance to national security that it could safely be permitted to appear in a foreign language!…”