Meeting Abstract
The fossil record is the most valuable source of historical data regarding organismal response to climate change. Conservation paleobiology has focused on changes in species abundance, range size shifts, & population dynamics inferences using ancient DNA. Few studies directly incorporate thermoregulatory capacity into historical models. One promising avenue to explore how changes in thermoregulatory capacity can influence climate-related survivorship is selective brain cooling (SBC) in even-toed ungulates. Artiodactyls can decouple brain from body temperature by up to 4ºC. SBC mitigates heat-stress & decreases evaporative water loss; as such it may insulate diversity as climate warms and dries. SBC is facilitated by an intracranial arterial meshwork called the carotid rete (CR), which replaces the internal carotid artery. Presence of a CR is accompanied by consistent remodeling of basicranial osteology, enabling direct tracing of enhanced artiodactyl thermoregulation in fossils. Using osteological correlates from 700 fossil specimens, SBC presence & absence was inferred for 279 extinct artiodactyl species. Of 24 extinct families, 14 lack SBC. Occurrence-based paleobiology modeling was used to calculate trait-specific Cenozoic diversification rates for artiodactyls with & without SBC. Results indicate negative speciation rates for artiodactyls without SBC during periods of aridification, ultimately resulting Miocene extinction. Contrarily, artiodactyls with SBC have increased diversification, even across environmental drying. By recent definitions, a structure is a key innovation if organisms that do not possess it are demonstrably more susceptible to extinction. SBC is a key innovation, implying that artiodactyls may be more amenable than other large mammal species to warming & drying climates.
