Global ecomorphological restructuring of dominant marine reptiles prior to the Cretaceous–Palaeogene mass extinction

Abstract

Mosasaurid squamates were the dominant amniote predators in marine ecosystems during most of the Late Cretaceous. Here, we use a suite of biomechanically rooted, functionally descriptive ratios in a framework adapted from population ecology to investigate how the morphofunctional disparity of mosasaurids evolved prior to the Cretaceous–Palaeogene (K/Pg) mass extinction. Our results suggest that taxonomic turnover in mosasaurid community composition from Campanian to Maastrichtian is reflected by a notable global increase in morphofunctional disparity, especially driving the North American record. Ecomorphospace occupation becomes polarized during the late Maastrichtian, with morphofunctional disparity plateauing in the Southern Hemisphere and decreasing in the Northern Hemisphere. We show that these changes are not strongly associated with mosasaurid size, but rather with the functional capacities of their skulls. Our novel approach indicates that mosasaurid morphofunctional disparity was in decline in multiple provincial communities before the K/Pg mass extinction, highlighting region-specific patterns of disparity evolution and the importance of assessing vertebrate extinctions both globally and locally. Ecomorphological differentiation in mosasaurid communities, coupled with declines in other formerly abundant marine reptile groups, indicates widespread restructuring of higher trophic levels in marine food webs was well underway when the K/Pg mass extinction took place.

Craniodental ecomorphology of the large Jurassic ichthyosaurian Temnodontosaurus

“…Tooth shape aspect ratio Tooth crown height/crown base diameter. Largest tooth chosen, both measurements from the same tooth Proxy for resistance to bite forces in tooth crown (Massare, 1987) Absolute tooth crown size Raw tooth crown height Correlates with prey size in cetaceans (Ridgeway & Harrison, 1999) and with gut content in fossil marine amniotes (Fischer, Bennion, et al, 2022) Relative snout depth Snout depth at midpoint/snout length Indication of reinforcement against high bite forces (Bennion et al, 2023;Fischer et al, 2016) Relative snout length Snout length (tip to orbit)/skull length Related to the hydrodynamics of the snout during prey capture (Bennion et al, 2023;MacLaren et al, 2022) Relative temporal musculature Temporal fenestra length/skull length Proxy for bite force and jaw musculature cross-sectional area (Bennion et al, 2023) Anterior mechanical advantage Distance between mandible articulation and tip of coronoid (preglenoid) process (jaw adductor inlever)/ mandible outlever length (articulation to tip)…”

“…Sander et al, 2021). Instead, we follow recent studies which specifically define the guild by its diet: megapredation (Bennion et al, 2023; Jiang et al, 2020; MacLaren et al, 2022) or hypercarnivory (De Andrade et al, 2010; Cortés et al, 2021). The most frequently used indications of a megapredatory lifestyle are features of the teeth, skull, and mandible (e.g.…”

Convergence and constraint in the cranial evolution of mosasaurid reptiles and early cetaceans

“…Mosasaurids, on the other hand, diversified into three parallel lineages early on in their evolutionary history (Russellosaurina, Mosasaurinae, and the more basal Halisaurinae), and radiated in a series of different waves until their extinction at the Cretaceous/Paleogene (K/Pg) boundary (Everhart 2005). Both mosasaurids and early cetaceans ultimately achieved near global distributions (Polcyn et al 2014; Buono et al 2019), high levels of taxonomic diversity (Polcyn et al 2014; Marx and Fordyce 2015), and notable craniodental disparity (Fitzgerald 2010; Boessenecker et al 2017b; Coombs et al 2022; Cross et al 2022; MacLaren et al 2022).…”

First Record of a Tylosaurine Mosasaur from the Latest Cretaceous Phosphates of Morocco

“…The Tylosaurinae, one of the longest-lived mosasaur lineages, first appeared in the Turonian as medium-sized generalists, though quickly evolved into giant macropredators by Coniacian-Santonian times [1] [2] [3] [4]. Consi-dered the top predators of Late Cretaceous marine environments, tylosaurine mosasaurs experienced a marked reduction in diversity and prevalence during the mid-Campanian that persisted until their extinction at the end of the Cretaceous [5] [6] [7].…”

“…The increased rarity of tylosaurine mosasaurs in the Maastrichtian is likely related to the diversification of several derived mosasaur lineages in the mid-Campanian [6] [7]. The evolution of specialized longirostrine plioplatecarpines, brevirostrine halisaurines, and durophagous mosasaurine taxa allowed for increased morphofunctional disparity at the expense of macropredatory generalists [8]- [13].…”