MARINE MESOZOIC REVOLUTION (MMR): COMMUNITY STRUCTURE DURING A TIME OF BIOTIC ESCALATION AND EVOLUTIONARY DIVERSIFICATION

The Mesozoic Era (250-66 mya), bracketed by the end Permian and end Cretaceous mass extinctions, was a time of major restructuring of marine ecosystems, driven by the radiation of several important groups of predators in conjunction with an increase in anti-predatory prey adaptations and a decrease in the relative abundance of sessile, suspension feeding organisms. These associations support the Mid-Mesozoic Marine Revolution (MMR) theory, which states that predation was a major driver of these eco-evolutionary changes. Furthermore, increasing predator diversity, predation intensity, motility, and ecospace utilization, suggest that the ecological complexity of marine systems has increased over time as more specialized morphologies and functions have evolved. Here we present preliminary results of a large-scale project examining the changing dynamics of the western Tethyan marine ecosystem, spanning the Middle Triassic to Late Cretaceous.

We present three large (1000+ species) marine food webs from the Middle Triassic (Anisian), Middle Jurassic (Bathonian), and Early Cretaceous (Aptian) of western Tethys, comparing structural features of those webs that are closely tied to community functioning, dynamics and stability. Species-level network analysis revealed that while generalists prevailed in the Triassic, there was a shift towards more specialist feeding strategies later in the Mesozoic, and thus a reduction of connectance. Therefore, rates of functional diversification were lower than those of taxon origination rates. Furthermore, average food chain length shortened over time, partially a result of relatively greater primary consumer diversity in the Jurassic. As predicted by MMR theory, our data show an increase of functional diversity, but reductions of connectance, chain lengths, and network diameter suggest that communities became more tightly integrated. Our results to date show that trophic organization changed significantly during the MMR, raising questions of when modern marine community structure and dynamics were established.