Meeting Abstract
All extant crocodilians possess articulating dermal ossifications called osteoderms, which are commonly described as defensive structures against predators. However, casual observations in the literature have implied that crocodilian osteoderms do not fully mature until well after the hatchling stage, which is when the risk of predation is greatest. If osteoderms primarily serve a defensive function they may be expected to experience strong selection to appear earlier in ontogeny. Alternatively, many aspects of crocodilian locomotor, social, and feeding behavior are known to change markedly throughout ontogeny and would be expected to exert different kinds of selective pressures on crocodilians as they grow. Alternative hypotheses of osteoderm function can be tested in part by looking to see which selective pressure shift correlates with osteoderm development. I examined CT scans of individuals at varying ontogenetic stages to assess the timing of osteoderm development and compared it with expectations derived from four hypotheses: (1) osteoderms assist in thermoregulation in larger individuals; (2) their development is constrained by diet; (3) hatchlings are protected by adults and predator self-defense is only necessary later in life; (4) they act as armor in intraspecific conflicts over resources. Eight taxa were represented, including two particularly well-sampled ontogenetic series of Crocodylus niloticus and Caiman yacare. I found that different regions of the body develop osteoderms at different times, and that osteoderm maturation generally corresponded to a stage when individuals begin competing with adults for territories and resources, shortly before sexual maturity. Thus, the observed pattern is more consistent with osteoderms acting as defensive structures against conspecifics than any other proposed hypothesis.
