Published this week in Proceedings of the Royal Society B, the study evaluated hundreds of species of fossil clams to piece together a comprehensive evolutionary tree over hundreds of millions of years. University of Chicago scientists?"along with colleagues at the Smithsonian Institution, the UK's Natural History Museum and the Field Museum ?" found that one basic assumption made in most models can significantly distort the evolutionary picture, causing the scale of evolutionary recovery from a massive extinction to be off by as much as 400%.