Abstract: Although morphological skull characters are used to identify species or subspecies of the genus Trichechus, little information is available on the growth of the manatee skull. We examined the ossification of the skull of the Florida manatee (Trichechus manatus latirostris) with regard to its growth pattern. We observed ten sutures in 137 crania (70 males and 67 females). Based on these results, the sutures can be classified into two groups by their ossification pattern. The first group contains the maxilloincisive suture, median palatine suture, frontal suture, and coronal suture. This group begins to ossify early in growth. The age of suture closure does not differ among the sexes. The second group consists of sutures related to the basicranium. This group is characterised by slower ossification compared to the first group. Suture ossification in this group proceeds from anterior to posterior. In this suture series, ossification occurred at later ages in males than in females. A notable feature is the formation of the occipital bone. Ossification of the spheno-occipital synchondrosis occurred earlier than that of the occipital condyle. This pattern is unique among mammals, including the dugong. Osteological maturity was determined by the status of the sutures. The sutures of the basicranium ossify slowly, and thus they are more valuable in evaluating the growth status of the skull than those of the viscerocranium and calvaria. The supraoccipital-exoccipital synchondrosis was the last to begin ossification, starting when individuals were more than 15 y old and 11 y old in males and females, respectively. We conclude that the ossification of the basicranium exhibits a unique pattern in the Florida manatee and that it is possible to determine the osteological maturity of the skull from the ossification of the supraoccipital-exoccipital synchondrosis.

Key Words: Florida manatee, Trichechus manatus latirostris, osteological maturity, cranial sutures, age-related growth

Document Type: Research article

DOI: 10.1578/AM.35.1.2009.72

Page Numbers: 72-81