Evidence that more than a third of Paleozoic articulate brachiopod genera (Strophomenata) lived infaunally

The Strophomenata, which includes two large orders, the Strophomenida and Productida, was the largest group of Paleozoic brachiopods. Nearly all uncemented strophomenatans possessed an unusual concave brachial valve. Most of these animals have been considered to have lived epifaunally, but had they rested on the sea floor, not only would they have faced intense predation, but their physical instability would have been fatal. I conclude that nearly all strophomenatans, like similar, concavo-convex pectinid bivalves, lived infaunally by ejecting water to create a pit into which they descended, to be protected by sediment covering the concave valve. Strophomenatans have been discovered with this sediment preserved in place. If exhumed and turned upside down, a strophomenatan could have righted itself by squirting water. Many productides had anchoring spines, and some had hinge areas with stabilizing flanges. Small spines on the brachial valves of some productides served to trap disguising ...