Meeting Abstract
P1.77 Tuesday, Jan. 4 Development of the Batoid Synarcual CLAESON, Kerin M; Ohio University claeson@ohio.edu
Throughout the course of evolution, certain anatomical complexes stand out as significant innovations in the origin and radiation of major vertebrates clades. For Batoidea, the synarcual cartilage is one of those complexes. I examined the ontogeny of the synarcual across batoids and evaluated the element’s variation across deep time. Comparing multiple taxa indicates heterochronic shifts in vertebral chondrification, fusion, and calcification. Ontogenetic sequences are generally conserved among several taxa within larger clades. The synarcual forms by the coalescence of several vertebral chondrification centers. In early stages, a short synarcual surrounds the first free vertebral centrum. At later stages additional neural arch segments are incorporated from anterior to posterior, until segment addition ceases, and the relative length of the synarcual cartilage to total length of the body normalizes. Axial cross sections of relatively later stage embryos show that the dorsal component of the synarcual is not fully fused at the midline. This indicates a secondary direction of chondrification, from ventral to dorsal, before meeting at the midline and eventually fusing with the median crest cartilage. CT scans and cleared and stained specimens of juveniles and subadults show that synarcual calcification is relatively late compared to the calcification of other regions of the skeleton. Additionally, comparison of embryonic, juvenile, and mature specimens of some batoids indicates that there is a fundamental difference between the pattern of chondrification and calcification that may be correlated to function. Identifying shifts in these patterns is critical before conducting a phylogenetic study of the clade. Until additional ontogenetic sequences of key taxa are obtained, ontogenetically relevant characters with a high likelihood of functional interference should be excluded from character delimitation.
