CHANGES IN THE FUNCTIONAL DIVERSITY OF MESOZOIC MARINE GASTROPODS

During the Mesozoic Marine Revolution (MMR), increasing predation pressure is thought to have resulted in ecosystem reorganization due to changes in ecospace utilization, richness, and new modes of life. Although Mesozoic gastropod shell architecture and diversity have been well studied, changes in gastropod functional diversity have not yet been directly evaluated using trait-based approaches.

Here we examine functional diversity, the number and types of functions performed by organisms in a community. To assess how gastropod functional diversity may have changed across the MMR in the western Tethys, we examined how species were distributed within functional space for 5 stage time-bins: the Anisian, Carnian, Bathonian, Aptian, and Maastrichtian. Functional diversity was quantitatively assessed using a Functional Entities (FEs) approach. Species with similar traits are thought to perform similar ecosystem functions, thus, for 642 gastropod species feeding habit, motility, and tiering were classified to create unique FEs. Differences in trait composition between stages should correspond to differences in functional composition, that is relating to trophic structure, tiering, and animal-substrate interactions in benthic ecosystems. The number of FEs ranged from 5 to 16, and functional vulnerability (no. species/no. FEs) increased from 22.2 during the Anisian to 35.7 in the Aptian, as functional groups were occupied by fewer species, but declined to 20 in the Maastrichtian. Functional redundancy, the percentage of FEs with only 1 species, corresponded with species richness, a pattern we observe in other paleocommunities, suggesting that species richness may play a large role in buffering ecosystems against the loss of functional diversity. These findings support the hypothesis that metabolic and physiological escalation during the MMR prompted significant ecosystem restructuring and changes in energy transfer pathways.