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Cephalic vasculature is an integral component of the vertebrate head, having a major effect on morphological organization, physiological processes, and various mechanical functions (e.g., erectile tissues). It is thus surprising that so little is known about cephalic vasculature in Archosauria, a major amniote clade that today includes crocodilians and birds and in the past included non-avian dinosaurs, pterosaurs, and a variety of basal forms. No comparative studies exist on archosaur head vasculature and no previous attempt has been made to determine homologous structures and patterns across Archosauria. Better understanding of archosaur head vasculature is key to interpreting and reconstructing the evolution of heads and head vasculature in amniotes. This study addresses this problem by documenting and comparing cephalic vascular structures and patterns in the extant archosaur clades Crocodylia ( Alligator mississippiensis, Crocodylus spp.) and Aves ( Anas platyrhynchos, Struthio ) and makes hypotheses of homology based on similarity. Data were attained from a variety of techniques including vascular injection, gross dissection, production of vascular corrosion casts, and the development of a novel stereoangiographic technique. Emphasis is given to the relationships of vessels to other soft-tissue structures and the bony skull, and causal associations between vascular structures and their osteological correlates are identified. These findings are discussed in light of the radical morphological changes that occur in birds (e.g., brain enlargement) and crocodilians (e.g., basicranial metamorphosis) to produce theirhighly apomorphic head anatomies that considerably deviate from the ancestral condition and were hypothesized to significantly effect and alter head vasculature in extant archosaurs. The striking conclusion of the research is that despite their different cephalic morphologies, the vascular structures and patterns in Aves and Crocodylia are very similar. In several areas these vascular structures had clear osteological correlates shared by the two clades, and that are identifiable in fossil archosaurs. Crocodilians and birds share several, interconnected, potential vascular physiological devices that would allow for brain temperature regulation. This interconnected network may further serve as a transport system for products produced in the Harderian gland and retina to the brain.
Document number: ohiou1020692011.
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