title: Eutherians experienced elevated evolutionary rates in the immediate aftermath of the Cretaceous-Palaeogene mass extinction.
abstract: The effect of the Cretaceous-Palaeogene (K-Pg) mass extinction on the evolution of many groups, including placental mammals, has been hotly debated. The fossil record suggests a sudden adaptive radiation of placentals immediately after the event, but several recent quantitative analyses have reconstructed no significant increase in either clade origination rates or rates of character evolution in the Palaeocene. Here we use stochastic methods to date a recent phylogenetic analysis of Cretaceous and Palaeocene mammals and show that Placentalia likely originated in the Late Cretaceous, but that most intraordinal diversification occurred during the earliest Palaeocene. This analysis reconstructs fewer than 10 placental mammal lineages crossing the K-Pg boundary. Moreover, we show that rates of morphological evolution in the 5 Myr interval immediately after the K-Pg mass extinction are three times higher than background rates during the Cretaceous. These results suggest that the K-Pg mass extinction had a marked impact on placental mammal diversification, supporting the view that an evolutionary radiation occurred as placental lineages invaded new ecological niches during the Early Palaeocene.
authors.affiliation: Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK thomas.halliday.11@ucl.ac.uk.
authors.forename: Thomas John Dixon
authors.identifier: 0000-0002-4077-732X
authors.initials: TJ
authors.lastname: Halliday
authors.affiliation: Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Upchurch
authors.affiliation: Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Anjali
authors.initials: A
authors.lastname: Goswami
mesh_terms: D000818:Animals; D005075:Biological Evolution; D000073566:Eutheria / Q000145:classification*; D053476:Extinction, Biological; D005580:Fossils; D010802:Phylogeny
keywords: Cretaceous; Palaeogene; evolutionary rate; extinction; mammals; radiation