Meeting Abstract
Osteostraci are the extinct jawless sister group to jawed vertebrates. As close relatives of early jawed vertebrates they share numerous characters, such as paired fins and an epicercal tail. Study of the functional morphology of this group has been restricted to qualitative discussion. Based on gross anatomical features, osteostracans have been proposed to have a benthic lifestyle. Study of the functional morphology of early vertebrates, such as osteostracans with contemporary benthic jawed vertebrates, will require suitable model organisms for the behaviours of interest. Dispersal, foraging ability, and escape responses of vertebrates are dependent on locomotor mode. The body and tail shape of a basal osteostracan, Ateleaspis tessellata is consistent with that of a modern benthic vertebrate and therefore might share similar locomotor mode. Here we suggest that some shark species represent suitable models for hypothesizing locomotion of osteostracans: they have similar body shape, an epicercal tail, and dorsal fins with a persistent shape and less control than ray-finned fishes. Here, the morphology of Ateleaspis, reconstructed from nearly complete specimens, is compared to four shark species including pelagic, demersal, and benthic taxa, to predict locomotor mode: dorsal fin position, heterocercal tail angle, aspect ratio of the tail, as well as the presence or absence of other anatomical features. Ateleaspis most closely resembles the benthic bamboo sharks, Chiloscyllium plagiosum, in aspect ratio, position of the first dorsal fin, and angle of the dorsal lobe of the tail and absence of a ventral lobe of the caudal fin. This is the first quantitative study of osteostracan functional morphology and locomotion.
