AN EON OF THE MIND: A COGNITIVE AND BEHAVIORAL VIEW OF PHANEROZOIC FAUNAS

Cognition, the ability to acquire and process information, mediates many critical interactions organisms have with their surrounding environments and with one another. The Cambrian radiation ushered in a world dominated by animals with behavioral repertoires and life modes reliant on complex information processing, using well-organized sensory and nervous systems. Comparisons among major Lagerstätten reveal Cambrian marine faunas to be similar to those later in the Phanerozoic in proportions of genera with macroscopic photoreceptive and chemoreceptive organs, as well as brains. Analysis of ecospace use by marine animals of four differing grades of nervous system complexity show that, both in the Cambrian and today, diverse habitat tiers and feeding modes can be occupied by those with even simple nervous systems. However, ecological lifestyles requiring rapid and routine movement are nearly exclusively associated within brain-bearing taxa, suggesting a connection with fast information processing abilities and bodily responses. The biosphere became further dominated by brain-bearing, behaviorally active faunas with the conquest of the land. The overall rise in cognitive sophistication in the Cambrian was likely a unique event in the history of life, though sensory system elaboration and increases in brain size have later developed in some lineages. Comparisons of behavioral categories studied by contemporary biologists with the paleontological literature also suggest that much of the behavioral repertoire observed in modern animals was present throughout the Phanerozoic from the Cambrian onwards.