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Species and Speciation in the Fossil Record$
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Warren D. Allmon and Margaret M. Yacobucci

Print publication date: 2016

Print ISBN-13: 9780226377445

Published to Chicago Scholarship Online: May 2017

DOI: 10.7208/chicago/9780226377582.001.0001

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Geographic Clines, Chronoclines, and the Fossil Record: Implications for Speciation Theory

Geographic Clines, Chronoclines, and the Fossil Record: Implications for Speciation Theory

(p.389) Chapter Fourteen Geographic Clines, Chronoclines, and the Fossil Record: Implications for Speciation Theory
Species and Speciation in the Fossil Record

Donald R. Prothero

Valerie J. Syverson

Kristina R. Raymond

Meena Madan

Sarah Molina

Ashley Fragomeni

Sylvana DeSantis

Anastasiya Sutyagina

Gina L. Gage

University of Chicago Press

Conventional evolutionary biology has long emphasized the importance of fragmentation of variable populations within geographic clines in the production of new species. The same kind of thinking has been applied to chronoclines in the fossil record, and how to define new species by breaking up continuous anagenetic sequences. The assumption is that geographic clines and chronoclines are formed by similar environmental influences, such as changes in temperature and other climatic variables. However, detailed studies of most of the common fossil birds and mammals at Rancho la Brea tar pits that lived over the past 35,000 years show that they are static over the entire range of climate changes of the last glacial-interglacial cycle, and show no changes that might be responses to the peak glacial cooling and climate changes of 20,000 years ago. Yet most of these same fossil birds and mammals have close living relatives (usually in the same genus) that show very strong clinal size and morphological changes, typically following Bergmann’s Rule and/or Allen’s rule. Thus, the processes that form geographic clines are not necessarily relevant to understanding change (or lack thereof) of morphology or size in the fossil record.

Keywords:   mammals, species problem, punctuated equilibrium

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