Brawn before brains in placental mammals after the end-Cretaceous extinction

Ornella Bertrand, Sarah Shelley, Thomas E. Williamson, John R. Wible, Stephen G. B. Chester, John J. Flynn, Luke T. Holbrook, Tyler R. Lyson, Jin Meng, Ian M. Miller, Hans Puschel Rouliez, Thierry Smith, Michelle Spaulding, Z. Jack Tseng, Steve Brusatte

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Mammals are the most encephalized vertebrates, with the largest brains relative to body size. Placental mammals have particularly enlarged brains, with expanded neocortices for sensory integration, the origins of which are unclear. We used computed tomography scans of newly discovered Paleocene fossils to show that contrary to the convention that mammal brains have steadily enlarged over time, early placentals initially decreased their relative brain sizes because body mass increased at a faster rate. Later in the Eocene, multiple crown lineages independently acquired highly encephalized brains through marked growth in sensory regions. We argue that the placental radiation initially emphasized increases in body size as extinction survivors filled vacant niches. Brains eventually became larger as ecosystems saturated and competition intensified.
Original languageEnglish
Pages (from-to)80-85
Issue number6588
Publication statusPublished - 1 Apr 2022


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