SAMPLING, STASIS AND SNOW: RESOLVING GAPS IN THE LATE PALEOZOIC FISH RECORD

“Gaps” between molecular clock estimates and fossil data exist in a wide variety of groups. One such gap exists for the origin of the teleosts, the most numerous and diverse group of the ray-finned fishes. The earliest fossil remains of teleosts are from the Mesozoic period (252-65 mya). However, molecular clock estimates place the origin of the teleosts during the Late Paleozoic Ice Age, 100 million years earlier. The source of this gap has been attributed to the fact that collections of fish material from the Permo-Carboniferous (P-C) have not been comprehensively examined in decades. During the Late Paleozoic Ice Age invertebrate morphological diversity and origination rates were depressed and taxa became more cosmopolitan, inducing a period of global ‘stasis’ and homogeneity. This raises the possibility that fish evolutionary rates may have likewise slowed down, violating the assumptions of molecular clocks and pinning the “gap” on incorrect models. In addressing this problem it is essential to determine what effect, if any, the global climatic conditions of the Late Paleozoic Ice Age had on actinopterygian evolution. We examined biogeographic patterns and changes in faunal composition in P-C ray-finned fishes to determine whether or not they experienced the same evolutionary stasis as invertebrates during this time. Because “gaps” between molecular evidence and the fossil record are found in a wide variety of groups, their causes and implications are central to understanding major patterns in the history of life. Ray-finned fishes represent an ideal opportunity to investigate the source of these “gaps” because the spectacular diversity of living actinopterygians is complemented by a rich fossil record.