LATE DEVONIAN CONTROLS ON POST-EXTINCTION REBOUND AND BIOGEOGRAPHIC RADIATION: EVIDENCE FROM ECHINODERMS

Famennian (Late Devonian) and earliest Carboniferous echinoderms historically have been poorly known, resulting in interpretations of prolonged rebound from the Devonian extinction events and overemphasis of a Frasnian/Famennian event. Climatic instability and/or meteorite impacts are commonly cited triggers for the events, but we believe that tropical mountain building and resulting sedimentation played a major role in defining biogeographic patterns of extinction and rebound of turbidity-sensitive tropical communities. Recent discoveries of abundant and diverse Famennian echinoderm faunas from northwestern China, Colorado, Australia, Morocco, and central Iran, together with re-examination of previously known Famennian echinoderm faunas from Germany and England indicate that overall Famennian echinoderm diversity and abundance are nearly five times greater than previously interpreted with predominantly a North American and Western European dataset. We interpret the paucity of Late Devonian echinoderm faunas in North American and western Europe as the result of a tectonic megabias because Famennian echinoderm faunas are diverse and widely distributed in an array of tropical shallow-marine environments not affected by tectonically-driven siliciclastic sedimentation. Famennian echinoderms are "forward looking" to the Carboniferous in taxonomy and morphologic innovation, although Famennian echinoderm faunas show a dearth of camerate crinoids that typify both older and younger faunas. From a biogeographic perspective, Laurasian faunas from China and Western Europe have many genera in common, but Gondwanan faunas do not. In general, we recognize the following trends: 1) the Frasnian/Famennian extinction event is overemphasized by tectonic megabiases; 2) echinoderm extinction rebound occurred earlier than previously thought; 3) higher-level taxonomy was not as well established as in older and younger faunas; and 4) biogeographic endemism was less prevalent than in older and younger faunas.