BENDER, G.*; MURRAY, B. P.; CLARK, K.; GILBERT, S. F.: EVIDENCE FOR THE NEURAL CREST ORIGIN OF THE TURTLE PLASTRON

The migrating cranial neural crest cells of birds, fish, and mammals have been shown to form the membranous bones of the cranium and face. These findings have been extrapolated to suggest that all the dermal bones of the vertebrate exoskeleton are derived from the neural crest ectomesenchyme. However, only one group of extant animals, the Chelonians, has an extensive bony exoskeleton in the trunk. We have previously shown that the autapomorphic carapacial and plastron bones of the turtle shell arise from intramembranous ossification. We have stained the 50-day developing plastron bones of the red-eared slider turtle Trachemys scripta with antibodies to two neural crest cell markers, HNK-1 and PDGFR&alpha. Each of the bones of the plastron stain positively for these markers of neural crest cells, strongly suggesting that these plastron bones are of neural crest origin. This extends the hypothesis of the neural crest origin of the exoskeleton to include the turtle plastron. If this is the case, either the turtle cranial crest has acquired the ability to move posteriorly into the trunk, or alternatively, the trunk neural crest cells have acquired (or re-acquired) the ability to form bone.