Post-Paleozoic Trends in the Abundance of Benthic Marine Organisms: Increasing Skeletal Abundance in Shallow-Marine Environments over the past 250 million years

Variations in skeletal abundance through geological history, when combined with organismal body size, can provide a much-improved quantification of animal abundance in marine environments, an important control on energy and nutrient flow through such systems. Increases in abundance have long been hypothesized to explain the increase in taxonomic diversity and mean animal body size in marine communities during the post-Paleozoic (252 Mya - Present) but total biomass has remained more poorly constrained than taxonomic diversity and body size due to the challenge of collecting relevant data. For this study, the abundance of skeletal fossils in marine limestones from the earliest Triassic through the Neogene (252 - 0 Mya) was evaluated in order to more directly quantify the absolute abundance of skeletal animals, algae, and foraminifera in marine carbonate environments. Absolute abundance data were collected from thirteen previously published papers reporting point count data for 1596 rock samples totaling to around 400,000 individual points. These data were recorded along with the geologic age, depositional environment, and standardized at the phylum and class level. An increase in the abundance of calcifying organisms across the post-Paleozoic was found, with the exception of a short-term decline following a major mass extinction event at the end of the Triassic period (201 Mya). These findings support the hypothesis that the abundance of marine biota has increased since the start of the Mesozoic, suggesting that increased trophic resources were at least one factor enabling the increases in taxonomic diversity. These and similar findings also have implications for modern conservation efforts. Conservationists can use these data as a deep-time baseline against which to compare changes in abundances within modern marine environments to identify ecosystems most in need of protection.