219-8 The Revolution of Small Snails and the Early Modern Evolutionary Fauna

Session: Paleontology, Diversity, Extinction, Origination (Posters)

Presenting Author:

Author:

Abstract:

The species richness and the shell size distributions of major clades and functional groups among gastropods, a key element of the Modern Evolutionary Fauna (MEF), underline the dominant role at modern tropical latitudes of carnivorous Caenogastropoda (particularly the Neogastropoda) and Heterobranchia, including small-sized ectoparasites and micrograzers. The escalation hypothesis emphasises prey-predator interactions as gastropods’ macroevolutionary drivers during the Mesozoic Marine Revolution, but overlooks the significance of the highly-diversified smaller species. Furthermore, the early Mesozoic roots of the Neogastropoda — active predators radiating in the Late Cretaceous, when their energy budgets increased — are poorly understood.

After revising the distribution of modern diversities and adaptations, I look at the tropical fossil record of the Permian-Triassic mass extinction (PTME), the major in animal history, and the Triassic rise of the MEF. The study suggests that: 1) non-carnivorous species dominated the gastropod fauna immediately before and after the PTME; 2) Permian micrograzers mainly fed on sponges and their microbial communities and waned during the early rise of the MEF; 3) ectoparasites and micrograzing carnivores, including stem neogastropods, diversified in the second part of the Middle Triassic, in coincidence with the advent of scleractinian corals and echinoderms of modern type; 4) larger predators are lacking throughout the study interval.

I conclude that patterns of gastropod species richness, size and form, the fossil record of reef-builders and other benthic invertebrates, and the shell morphology of stem neogastropods jointly highlight a Middle Triassic revolution among small-sized gastropods triggered by the emergence of scleractinian corals and the diversification of echinoderms. Habitat heterogeneity and new food sources offered niches for the early radiation of modern gastropod clades, pointing Middle Triassic shallow-marine, tropical ecosystems as the cradle of the MEF.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7750

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