AERODYNAMICS AND THERMOREGULATORY FUNCTION OF THE DORSAL SAIL OF EDAPHOSAURUS

Dorsal sails supported by hyperelongate neural spines of dorsal verteb rae were evolved by various tetrapods, but most work on their function has centered on the pelycosaur Dimetrodon, in which the sail has gene rally been interpreted as a thermoregulatory structure that would perm it rapid warming in the morning and cooling during the hot midday. The pelycosaur Edaphosaurus differed from other sailed tetrapods in that the neural spines supporting the sail had laterally directed tubercles or cross-bars. Fast interpretations of Edaphosaurus suggested that th e cross-bars were embedded in a thick fat-storage structure or extende d from a thin sail to enhance its utility for intraspecific display. H owever, wind tunnel modeling of airflow over-a thin sail with laterall y projecting cross-bars supports a thermoregulatory interpretation of the sail of Edaphosaurus. The cross-bars would produce a turbulent flo w, which would increase the effectiveness of convective cooling. Measu rements of heat flow in an instrumented model show that cross-bars inc rease heat loss from the sail. The cross-bars may have enabled Edaphos aurus to thermoregulate effectively with a smaller and lower dorsal sa il than would have been required without them.