High-performance suction feeding in an early elasmobranch.

Abstract

High-performance suction feeding is often presented as a classic innovation of ray-finned fishes, likely contributing to their remarkable evolutionary success, whereas sharks, with seemingly less sophisticated jaws, are generally portrayed as morphologically conservative throughout their history. Here, using a combination of computational modeling, physical modeling, and quantitative three-dimensional motion simulation, we analyze the cranial skeleton of one of the earliest known stem elasmobranchs, <i>Tristychius arcuatus</i> from the Middle Mississippian of Scotland. The feeding apparatus is revealed as highly derived, capable of substantial oral expansion, and with clear potential for high-performance suction feeding some 50 million years before the earliest osteichthyan equivalent. This exceptional jaw performance is not apparent from standard measures of ecomorphospace using two-dimensional data. <i>Tristychius</i> signals the emergence of entirely new chondrichthyan ecomorphologies in the aftermath of the end-Devonian extinction and highlights sharks as significant innovators in the early radiation of the modern vertebrate biota.