"This database is the first ever; no other database of this kind exists for any interval of geologic time, from which to study geographic patterns of macroevolution," Powell said.
According to Powell's analysis, brachiopods that lived primarily near the equator suffered the highest extinction rates and did not re-appear in great numbers until the ice age ended.
"The absence of these particular brachiopods during the ice age left the oceans populated almost entirely with those who lived over a wider geographic area," Powell said. "What I found is that the uniquely low global rates of evolution and extinction for brachiopods during the late Paleozoic ice age were caused by the loss and lack of recovery of those that had existed in narrow latitudinal ranges."
Powell believes that those brachiopods that existed within narrow latitudinal ranges became victims of the extremes in the annual minimum and maximum temperatures that were typical of the late Paleozoic. During that era, "seasonality" -- the difference between annual temperatures' highs and lows -- was amplified by the presence of glaciers.
"I've suggested that those brachiopods which eventually became extinct had adapted only to small temperature changes, and thus did not survive," he said. "The other competing hypothesis is that large fluctuations of sea level, driven by the melting and reforming of glaciers, disrupted marine communities, and the ones which survived were those able to adjust.