INNOVATIVE TECHNIQUES REVEAL INNOVATIVE FISH: SOPHISTICATED SHARKS IN AN EXTINCTION AFTERMATH

We use 3D imaging and printing to discover the morphology and kinematics of an unexpectedly advanced jaw system in a Mississippian shark from Scotland. Enhanced suction feeding is a textbook innovation of ray-finned fishes, and has contributed to explanations of their superabundant taxonomic diversity and morphological disparity. Sharks, on the other hand, are argued to be morphologically constrained throughout their history and slow to generate novelty and diversity. Such assumptions are difficult to challenge when faced with a fossil record of little more than isolated teeth, occasional body outlines, and, more rarely, portions of cartilage skeleton. Here we show how 3D technologies have released a wealth of information on one particular shark from the Viséan of Scotland, revealing associated and partly articulated skeletons preserved within ironstone nodules. Data quality allowed 3D modeling of the braincase, jaws, and jaw suspension skeleton both virtually and physically. In turn, these data allowed 3D kinematic analysis, exploring multi-bar linkage networks and estimates of oral volume change in the reconstructed bite cycle. The results present a suction feeding mechanism resembling, but non-identical to, examples familiar from modern fishes. Such mechanisms are unknown in any Paleozoic fish pre-dating the Permian, and this chondrichthyan example occurs some 50+ million years before the earliest evidence of similar jaws in an osteichthyan. In addition to revealing that early sharks achieved high levels of cranial biomechanical complexity, these data also imply emergence of entirely new ecomorphologies and niche-spaces in the aftermath of the end-Devonian extinction, adding to our changing appreciation of sharks as early innovators in the evolutionary radiation of crown group gnathostomes and advent of the modern vertebrate biota.