Northward range extension of a diminutive-sized mammal (Ectocion parvus) and the implication of body size change during the Paleocene–Eocene Thermal Maximum

• Published in: Palaeogeography, palaeoclimatology, palaeoecology Vol. 363-364; pp. 144 - 150
• Main Author: Burger, Benjamin John
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.11.2012
• Subjects: Biogeography; Carbon isotopes; Eocene; Global warming; Paleocene; Piceance Creek; USA, Wyoming, Bighorn Basin; USA, Wyoming; USA, Colorado; Biogeography; Eocene; Global warming; Piceance Creek; Carbon isotopes; Paleocene
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2012.09.008

An abrupt global warming event marks the Paleocene–Eocene boundary, known as the Paleocene–Eocene Thermal Maximum (PETM). The event is distinguished in the strata globally by a significant negative excursion of δ13C ratio values. The response of the terrestrial biota to the abrupt climatic change has been well studied in northern Wyoming in the Bighorn Basin, where it has been observed that the mammalian fauna during the global warming event is represented by smaller, but morphologically similar species to those found later in the Eocene. Various hypotheses have been proposed to explain the observation smaller body sizes during the global warming event. In this article, evidence is presented to support the hypothesis that the observed body size decrease during the PETM was influenced by the appearance of smaller southern species who extended their geographic range northward during the abnormal global warming event. Using disperse organic carbon isotopic ratios of bulk sediment, the negative excursion of δ13C was located in the Piceance Creek Basin of western Colorado, 400km to the south of the Bighorn Basin. Below the stratigraphic level marking the negative carbon excursion in the Piceance Creek Basin are five specimens of the phenacodontid mammal (Ectocion parvus), a diminutive species of the genus Ectocion restricted to the basal Eocene (Wa-0 Biozone) in northern Wyoming. The five specimens of E. parvus are associated with a late Paleocene (Clarkforkian) mammalian fauna in Colorado, implying that the diminutive species extended its geographic range northward during the global warming event. This evidence supports biogeographic models that assume poleward biogeographic shifts during global warming events, and will have modern day implications for the conservation of species as global temperatures rise in the near future. ► A global warming event marks the Paleocene–Eocene boundary. ► Diminutive sized mammals occur at the Paleocene–Eocene boundary in Wyoming. ► Correlated Paleocene–Eocene boundary between Colorado and Wyoming. ► Discovered diminutive mammal species in Colorado prior to boundary. ► Proposed that the species extended its range northward during global warming event.