title: Repetitive mammalian dwarfing during ancient greenhouse warming events.
abstract: Abrupt perturbations of the global carbon cycle during the early Eocene are associated with rapid global warming events, which are analogous in many ways to present greenhouse warming. Mammal dwarfing has been observed, along with other changes in community structure, during the largest of these ancient global warming events, known as the Paleocene-Eocene Thermal Maximum [PETM; ~56 million years ago (Ma)]. We show that mammalian dwarfing accompanied the subsequent, smaller-magnitude warming event known as Eocene Thermal Maximum 2 [ETM2 (~53 Ma)]. Statistically significant decrease in body size during ETM2 is observed in two of four taxonomic groups analyzed in this study and is most clearly observed in early equids (horses). During ETM2, the best-sampled lineage of equids decreased in size by ~14%, as opposed to ~30% during the PETM. Thus, dwarfing appears to be a common evolutionary response of some mammals during past global warming events, and the extent of dwarfing seems related to the magnitude of the event.
authors.affiliation: Department of Earth Sciences, University of New Hampshire, 56 College Road, Durham, NH 03824, USA.
authors.forename: Abigail R
authors.initials: AR
authors.lastname: D'Ambrosia
authors.affiliation: Department of Earth Sciences, University of New Hampshire, 56 College Road, Durham, NH 03824, USA.
authors.forename: William C
authors.identifier: 0000-0001-8814-3409
authors.initials: WC
authors.lastname: Clyde
authors.affiliation: Department of Geology, Colorado College, 14 East Cache La Poudre Street, Colorado Springs, CO 80903, USA.
authors.forename: Henry C
authors.initials: HC
authors.lastname: Fricke
authors.affiliation: Museum of Paleontology and Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Philip D
authors.identifier: 0000-0002-1550-2674
authors.initials: PD
authors.lastname: Gingerich
authors.affiliation: Department of Geosciences and Engineering, Delft University of Technology, Stevinweg 1, 2628 CN Delft, Netherlands.
authors.forename: Hemmo A
authors.identifier: 0000-0001-7648-3369
authors.initials: HA
authors.lastname: Abels
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D005580:Fossils; D017752:Greenhouse Effect; D006736:Horses / Q000033:anatomy & histology / Q000502:physiology
keywords: Eocene; body size; climate; dwarfing; hyperthermal; mammal; stable isotopes