title: The extended Price equation quantifies species selection on mammalian body size across the Palaeocene/Eocene Thermal Maximum.
abstract: Species selection, covariation of species' traits with their net diversification rates, is an important component of macroevolution. Most studies have relied on indirect evidence for its operation and have not quantified its strength relative to other macroevolutionary forces. We use an extension of the Price equation to quantify the mechanisms of body size macroevolution in mammals from the latest Palaeocene and earliest Eocene of the Bighorn and Clarks Fork Basins of Wyoming. Dwarfing of mammalian taxa across the Palaeocene/Eocene Thermal Maximum (PETM), an intense, brief warming event that occurred at approximately 56 Ma, has been suggested to reflect anagenetic change and the immigration of small bodied-mammals, but might also be attributable to species selection. Using previously reconstructed ancestor-descendant relationships, we partitioned change in mean mammalian body size into three distinct mechanisms: species selection operating on resident mammals, anagenetic change within resident mammalian lineages and change due to immigrants. The remarkable decrease in mean body size across the warming event occurred through anagenetic change and immigration. Species selection also was strong across the PETM but, intriguingly, favoured larger-bodied species, implying some unknown mechanism(s) by which warming events affect macroevolution.
authors.affiliation: Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, Canada AB T2N 1N4 Museum of Paleontology, University of California, 1101 Valley Life Sciences Building, Berkeley, CA 94720, USA bdrankin@berkeley.edu.
authors.forename: Brian D
authors.initials: BD
authors.lastname: Rankin
authors.affiliation: Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, Canada AB T2N 1N4.
authors.forename: Jeremy W
authors.initials: JW
authors.lastname: Fox
authors.affiliation: Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, Canada AB T2N 1N4.
authors.forename: Christian R
authors.initials: CR
authors.lastname: Barrón-Ortiz
authors.affiliation: Department of Anatomy, Western University of Health Sciences, 309 E. Second Street, Pomona, CA 91766, USA.
authors.forename: Amy E
authors.initials: AE
authors.lastname: Chew
authors.affiliation: Museum of Paleontology, University of California, 1101 Valley Life Sciences Building, Berkeley, CA 94720, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Holroyd
authors.affiliation: Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, Canada AB T2N 1N4.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Ludtke
authors.affiliation: Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, Canada AB T2N 1N4.
authors.forename: Xingkai
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, Canada AB T2N 1N4.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Theodor
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D057231:Climate Change; D005580:Fossils / Q000033:anatomy & histology*; D008322:Mammals / Q000033:anatomy & histology* / Q000502:physiology; D008954:Models, Biological; D013696:Temperature; D014959:Wyoming
keywords: Mammalia; Palaeocene/Eocene boundary; Price equation; body size; macroevolution; species selection