Head Features Diversified before Body Shapes and Types

Two radiations of ray-finned fishes (Actinopterygii), Carboniferous forms (facing left) and acanthomorph teleosts (facing right) underwent distinct cranial (feeding) and later postcranial (habitat) stages in trait diversification. Credit: Photographs by Lauren Sallan and Matt Friedman

By analyzing the physical features of fossil fish that diversified around the time of two separate extintion events, scientists from the University of Chicago and the University of Oxford found that head features diversified before body shapes and types. The discovery disputes previous models of adaptive radiations and suggests that feeding-related evolutionary pressures are the initial drivers of diversification.

"It seems like resources, feeding and diet are the most important factors at the initial stage," said lead author Lauren Sallan, graduate student in the Department of Organismal Biology and Anatomy at the University of Chicago. "Strange heads show up first – crushing jaws, animals with big teeth, with long jaws – but they're all pretty much attached to the same body." more here