Abstract :
[en] 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 within the Cenomanian-Turonian interval, a time known for its climatic volatility.
Our goal is to assess the impact of these Cenomanian-Turonian events on marine reptiles, by analysing extinction selectivity and changes in functional diversity. We carried out phylogeny-informed analyses of extinction selectivity, using Fritz & Purvis’ D metric on an informal supertree sampling 370 marine reptile lineages; we found that lineages’ extinctions are both elevated and selective during the ‘middle Cretaceous’, targeting different clades at each boundary. Then, we computed univariate and multivariate distributions of functional traits (vision range, approximated bite force, snout elongation) using the largest sample of 2D and 3D data on marine reptiles ever assembled. The weak morphological and functional convergence between Early and Late Cretaceous marine reptiles resulted in marine reptile assemblages that are clearly dissimilar not only in terms of phenotypes, but also in the biomechanical and functional aspects of their skulls. This highlights the importance of past extinction events in reshaping the highest tiers of marine trophic webs.
