Reappraisal of patterns of nonmarine cryptodiran turtle carotid circulation: evidence from osteological correlates and soft tissues.

The turtle cranial circulation has been employed as an important source of phylogenetic information, but recent conflicting hypotheses of relationship within Testudinata suggest reevaluation of the utility of characters drawn from this complex. As a component of a comprehensive character analysis, the osteological correlates of the nonmarine cryptodiran turtle carotid circulation are herein subjected to high-resolution X-ray computed tomography, reassessed, and statistically investigated. Three different patterns of osteological correlates, indicating three disparate cranial circulatory patterns, are described, and this finding is corroborated by evidence from circulatory soft tissues. Members of the Trionychia and Kinosternoidea exhibit patterns that differ from the more widespread condition found in testudinoid taxa. This result differs from previous work, which has indicated the presence of only two major cranial circulatory patterns, and suggests that while cranial circulatory features may be phylogenetically informative, the information contained within them indicates patterns of relationship different from those previously hypothesized.