HOW REAL WAS THE CAMBRIAN EXPLOSION OF MARINE LIFE?

‭The Cambrian explosion was a time of unique morphologic experimentation in the history of life. Numerous marine invertebrate phyla and classes, including many extinct groups, appeared abruptly in the fossil record during a brief interval lasting perhaps as little as five or ten million years. Subsequent diversification over the next five hundred million years produced relatively little in the way of higher taxa even after repeated episodes of mass extinction, leading paleontologists to propose explanatory mechanisms ranging from unique developmental flexibility to unique ecologic opportunity in the Cambrian. However, the rapid burst of morphologic innovation that characterizes the Cambrian explosion may be explainable, in part, as an artifact of fossil preservation. To help evaluate the extent of this possible bias, I employ‬ a mathematical branching model of taxonomic origination and extinction, together with observed preservation rates of known fossil taxa. The analysis suggests that large-bodied marine invertebrates are unlikely to have significantly predated the Cambrian, reinforcing the view that the Cambrian explosion was a real biologic event and not a preservational artifact. These results are consistent with the trace fossil record, which documents the equally explosive global transition from simple surface trails to larger, more complex burrows in the late Ediacaran and early Cambrian.