Paper No. 46-2
Presentation Time: 9:15 AM
EXAMINING THE ROLE OF SUBSTRATE PREFERENCE IN BRACHIOPOD DECLINE FOLLOWING JURASSIC RECOVERY USING THE PALEOBIOLOGY DATABASE
Brachiopods are a primary member of the Paleozoic evolutionary fauna, which dominated marine ecosystems between the early Ordovician and late Paleozoic. However, they are today restricted to various marginal habitats, having been almost entirely supplanted by bivalves in modern marine communities. Though brachiopods sharply declined during the Permian-Triassic event, a second decline occurred following a promising recovery in abundance and diversity during the Jurassic. It is hypothesized that a driving cause of this secondary decline was the increasing restriction of brachiopods to carbonate substrates, as opposed to softer, muddy substrates. Important ecological drivers of this environmental restriction include fouling by burrowing organisms as well as the susceptibility of brachiopod larvae to grazing organisms in the absence of cryptic environments, with increases in both behaviors coinciding with brachiopod decline. Indeed, most living brachiopod groups occur on hard, usually carbonate sediments, with the exception of a few minor groups. Lithological preference of brachiopods was compared to other major invertebrate groups including bivalves and gastropods over the time period. Though the declining proportion of carbonate occurrences in the Paleobiology Database reflects a sampling bias due to the increasing latitude of Europe and North America, careful statistical analysis allows for more accurate determination of substrate preference. Analysis of lithological data from over 100,000 brachiopod occurrences in the Paleobiology Database shows increasing preference for carbonate substrates over the course of the Mesozoic, compared to a more balanced lithological distribution during the Paleozoic.