How mid-Cretaceous events affected marine top predators

The highest trophic niches in Mesozoic oceans were occupied by multiple, loosely related clades of marine reptiles, which evolved a series of craniodental and postcranial morphologies. The Jurassic and Early Cretaceous are characterized by relative stability of higher taxonomic levels, with three main clades dominated trophic chains: ichthyosaurians, plesiosaurians, and thalattosuchian crocodyliformes. This macroevolutionary picture changes drastically during the ‘middle’ Cretaceous: ichthyosaurians, thalattosuchians, and pliosaurid plesiosaurians disappear, whereas mosasaurids and peculiar xenopsarian plesiosaurians diversify, alongside acanthomorph teleosts, neoselachian sharks, marine turtles, and marine birds. This shift created the unique and somewhat short-lived oceanic trophic webs of the Late Cretaceous. Many of these clade turnovers (although not all) are concentrated during the Cenomanian-Turonian interval, a time known for its climatic volatility.

Project SEASCAPE explores the long-term impact of environmental changes on extinct oceanic top predators. To do so, we combine two main datasets and approaches. Firstly, we carry out phylogeny-informed analyses of extinction selectivity, using a new informal supertree sampling 370 marine reptile lineages. Secondly, we compute macroevolutionary functional landscapes before and after the event(s), based on (to our knowledge) the largest sample of 2D and 3D data on marine reptiles ever assembled. We found that lineages’ extinctions are both elevated and selective during the ‘middle Cretaceous’, targeting different clades at each boundary. Our macroevolutionary functional landscapes show that the weak morphological and functional convergence between Early and Late Cretaceous marine reptiles resulted in assemblages that are clearly dissimilar not only in terms of phenotypes, but also exhibiting biomechanical and functional divergences. This highlights the importance of past extinction events in reshaping the highest tiers of marine trophic webs.