Eutherian morphological disparity across the end-Cretaceous mass extinction

Abstract

In the aftermaths of mass extinction events, during radiations of clades, and in several other evolutionary scenarios, there is often a decoupling of taxonomic diversity and morphological disparity. The placental mammal radiation after the end‐Cretaceous mass extinction is one of the archetypal adaptive radiations, but the change in morphological disparity of the entire skeleton has never been quantified across this important boundary. We reconstruct ancestral morphologies of 680 discrete morphological characters onto dated phylogenies of 177 mostly Cretaceous and Palaeogene eutherians (placental mammals and their stem relatives). Using a new approach to incorporate morphologies representing ghost lineages, we assess three measures of morphological disparity (sum of ranges, sum of variances and mean pairwise dissimilarity) across stage‐level time bins within the Cretaceous and Palaeogene. We find that the range‐based metric suggests that eutherian disparity increased immediately after the end‐Cretaceous mass extinction, while both variance‐based metrics declined from the Campanian to the Maastrichtian, but showed no change in disparity from the Maastrichtian to the Puercan – the first North American Land Mammal Age of the Paleocene. Increases in variance‐based metrics lag behind the range‐based metric and per‐lineage accumulation rate, suggesting that the response of mammals to the Cretaceous–Palaeogene event was characterized by an early radiation that increased overall morphospace occupation, followed later by specialization that resulted in increased dissimilarity.

Virtual endocranial and inner ear endocasts of the Paleocene ‘condylarth’ Chriacus: new insight into the neurosensory system and evolution of early placental mammals

“…The end‐Cretaceous cataclysm that killed off non‐avian dinosaurs and many other vertebrates about 66 million years ago provided placental mammals with a unique opportunity to thrive (Wible et al., ; O'Leary et al., ). Some 10 million years into the Paleogene, placental mammals had already displayed a clear increase in taxonomic and ecological diversity, as well as in evolutionary rates, in contrast to their end‐Cretaceous relatives (Alroy, ; Slater, ; Grossnickle & Newham, ; Halliday & Goswami, ,b; Halliday et al., ). This extrinsic environmental change definitively opened new ecological opportunities for placental mammals; however, intrinsic aspects of placental mammals likely played a role in their success as well (Wilson, ).…”

Therian mammals experience an ecomorphological radiation during the Late Cretaceous and selective extinction at the K–Pg boundary

“…While previous studies have identified taxonomic and ecomorphological diversification events of Mesozoic mammals, these events were largely confined to the Jurassic or involved in non-therian lineages [13 -17]. After the K -Pg extinction event, which eliminated non-avian dinosaurs, fossil evidence indicates immediate increases in therian body sizes, body size disparity, taxonomic diversity, and dietary diversity [1][2][3][4]6,8,9,11,18], implying that therian mammals adaptively radiated during the earliest Palaeocene [1]. Further, O'Leary et al [5] conclude that placental mammals radiated extremely rapidly in the first 200 000-400 000 years after the K -Pg extinction event.…”

The biogeography and ecology of Sri Lankan mammals point to conservation priorities

“…However, a reanalysis of the same data set along with new evidence placed the placental mammal origins substantially before the K-Pg boundary (Tarver et al, 2016), in keeping with earlier estimates Ji et al, 2002). These Eocene placentals, with pre-K-Pg roots, are the ancestors of modern mammalian groups (perissodactyls, artiodactyls, primates, rodents, and (Bowen et al, 2002;Solé and Smith, 2013;Halliday and Goswami, 2016). …”