Meeting Abstract
Embryological studies of vertebrate development have culminated in a model of the cartilaginous units which collectively contribute to formation of the chondrichthyan cranium. Developmental studies of neural crest and mesodermal cell contribution to the cranium have enhanced the embryological data. Yet, how complete is our understanding of chondrocranial development? How does this influence our interpretation of chondrocranial evolution? Are we missing something? In this work, we present evidence of Paleozoic fish with cranial designs that challenge our perceptions of what the early chondrocranium was like. A number of Paleozoic elasmobranchs, in contrast to extant forms, are now known to exhibit a chondrocranium comprised of two moieties. New data is now presented for a discontinuous chondrocranial design in non-elasmobranchian fishes from the Bear Gulch Limestone of Montana (323myo). This information is discussed with reference to data from acanthodian and osteichthyan fishes. This data on cranial design offer challenges from a developmental and evolutionary perspective to our concepts of the stem chondrichthyan and stem gnathostome design.
