P1.119 Wednesday, Jan. 4 Ontogeny and Phylogeny of Cranial Vascular Patterns in the Tragulidae (Artiodactyla: Ruminantia) O'BRIEN, Haley D.; Ohio University, Athens firstname.lastname@example.org
Most extant even-toed ungulates possess a highly specialized cranial vascular structure known as the carotid rete. The carotid rete is an intracranial thermoregulatory arterial meshwork capable of selectively cooling the brain. As such, the carotid rete is hypothesized to be selectively advantageous for artiodactyls. Within Artiodactyla, one of the most successful clades is the Ruminantia. All currently sampled ruminants possess a carotid rete except for Tragulus javanicus, a species within most basal ruminant family. Is the lack of a carotid rete a basal condition for ruminant cranial vascular patterns, or is there a secondary loss within Tragulidae? This study elucidates the evolutionary history of the carotid rete within the Tragulidae by examining phylogenetic and ontogenetic patterns of cranial vasculature.
Osteological correlates for cranial vascular patterns, including external cranial foramina and intracranial impressions (i.e. carotid canal), were scored for four species of tragulids: Hyemoschus aquaticus, Tragulus javanicus, Tragulus napu, and Tragulus stanleyanus. Osteological correlates and ancestral state reconstruction reveal a secondary loss of the carotid rete within Tragulidae. Neonate and juvenile crania of H. aquaticus and T. javanicus were studied to identify any ontogenetic patterns that may inform how this character is lost. The expansion of cartilaginous structures within external cranial foramina of T. javanicus indicates that the carotid rete is lost late in embryonic development, corroborating pre-existing evidence that an intracranial meshwork develops in early T. javanicus embryos, only to diminish significantly in neonates. These results strengthen the possibility that basal ruminants possessed this evolutionarily advantageous cranial vascular pattern.