FOR MODERN SHARKS TO RISE, THEY MUST FIRST SURVIVE AN ICE AGE

All modern sharks and rays form a monophyletic group, the Neoselachii, that has its origins in the middle Paleozoic Era. Sharks belonging to the family Anachronistidae are the oldest known clade of neoselachian sharks. Their teeth are defined as having a conical central cusp, prominent lateral blades, a labial visor which overhangs the crown-base junction, and a V-shaped notch in the underside of the root (in addition to typically neoselachian histological characteristics). The global biostratigraphy of anachronistid sharks indicates their persistence across numerous large-scale environmental perturbations such as the impact of the 38^th parallel meteoroids, the onset and decline of the late Paleozoic Ice age, and the Carboniferous-Permian Boundary. Given that neoselachians were able to survive both mass extinctions at the end of the Devonian Period, as well as the the Permo-Triassic extinction event, the ability of primitive members of this clade to persist across environmental changes may have been a significant factor in this group’s later success and diversification in the Mesozoic and Cenozoic Eras. A close examination of anachronistid biostratigraphy in the Conemaugh Group (Carboniferous, Pennsylvianian, Kasimovian to Gzhelian: 307 to 298 million years ago) reveals their persistence across no less than 6 intervals of sea level rise and fall. The resistance of anachronistids to sea-level induced extinction and extirpation may have been a factor in the ability of the Neosealchii to persist across much larger environmental changes such as the late Paleozoic Ice Age (with its own accompanying global sea level changes) and other late Paleozoic periods of faunal overturn.