Meeting Abstract

1.8  Jan. 4  Turtle Carotid Circulation: Ontogeny, Phylogeny, and Evolution JAMNICZKY, Heather A.; University of Calgary hajamnic@ucalgary.ca

The bony canals of the turtle skull associated with the cranial circulation have long been considered integral to our understanding of turtle systematics, both extinct and extant. Recent phylogenetic analyses employing a variety of data sets indicate alternatives to the traditional arrangement of crown turtles, and may have implications for extinct members of the clade. An integrative character analysis was therefore undertaken in order to re-examine the phylogenetic signal contained in this character complex. Quantitative reassessment of the osteological correlates of the turtle cranial circulation revealed that the initial, qualitative description of these characters is in need of revision. Further, the constraints of nominalism and a focus on size alone may have been confounding systematic analyses. Subsequent high-resolution x-ray computed tomography of extant specimens resulted a re-interpretation of primary homology among internal carotid branches in crown turtles, and re-evaluation and re-description of characters drawn from these features. Comparative embryology was employed to explore the origins of circulatory novelty and pattern divergence within the clade, resulting in the hypothesis that heterochrony has produced a circulatory morphology, exhibited in Trionychidae, that differs from the widely distributed and putatively primitive circulatory pattern. Character analysis such as this, employing information gleaned from multiple investigatory techniques applied to extinct and extant organisms, is necessary for effective homology determination and the generation of robust phylogenies for use in higher-level evolutionary inference.