Ordovician increase in extent and depth of bioturbation: Implications for understanding early Paleozoic ecospace utilization

Abstract

The infaunal habitat was colonized in the early Phanerozoic primarily by soft-bodied organisms. To understand the early biotic history of this environment, it is necessary to examine the overall record of bioturbation, or ichnofabric. We present here results documenting trends in ichnofabric from Ordovician strata of the Great Basin in California, Nevada, and Utah, collected by a method devised to semiquantitatively measure the extent of early Paleozoic utilization of infaunal ecospace. When combined with similar Cambrian data, a two-phase stepwise pattern of increasing bioturbation contemporaneous with the Cambrian and Ordovician radiations of skeletonized metazoans is apparent. These data represent evidence independent of the body fossil record of increasing ecospace utilization in the early Paleozoic.