Tragedy found in Cambrian carnival.

Paleontologists have come to view the early Cambrian period as an evoluntionary field day -- a time when the first complex animals exploded onto the scene, filling the seas with a rich assortment of life. But new research reveals that a wave of extinctions may have hit right in the middle of this evolutionary binge, decimating the ranks of the newly evolved creatures.

Philip W. Signor of the University of California, Davis, discovered the extinction evidence while compiling a global database of more than 850 genera living in the early Cambrian period, roughly 530 million years ago. As he looked at the individual stages of the period, Signor was surprised to find that a vast variety of animals had died out at the end of the Botomian stage, about 10 million years after the Cambrian's start. More than 80 percent of the genera present during this stage failed to survive into the next one, Signor reported in late June at the Fifth North American Paleontological Convention in Chicago. In terms of extinction rates, the early Cambrian die-offs rank as even more severe than those at the end of the Permian, which have been considered the greatest of the five known mass extinctions in Earth's history.

A confirmation of Signor's findings would make the Cambrian event the earliest known mass extinction and perhaps one of the worst. Like all such extinctions, the early Cambrian example would have redirected the course of evolution. In this case, Signor says, the die-offs wiped out most of the major groups, making possible the ascendancy of that most famous group of extinct invertebrates -- the trilobites.