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Timing and biogeography of the eutherian radiation: fossils and molecules compared
 

Summary: Timing and biogeography of the eutherian radiation:
fossils and molecules compared
J. David Archibald*
Department of Biology, San Diego State University, 5500 Campanile Dr., San Diego, CA 92182-4614, USA
Received 20 August 2002; revised 6 December 2002
Abstract
Theria includes Eutheria and its sister taxon Metatheria. Placentalia includes extant eutherians plus their most recent common
ancestor. The oldest eutherian is from 125 mya (million years ago). Molecular studies place this origin at about 130185 mya. Older
dates cannot be refuted based on fossil evidence as earliest eutherian remains are scarce. Earliest superordinal clades (hence Pla-
centalia) range from 64104 mya (median 84 mya) based on molecules, similar to 8590 mya based on fossils. Superordinal clades
Archonta, Ferungulata, Glires, and Paenungulata based on fossils are similar to molecularly based clades, except Afrotheria was not
predicted by fossils. Both fossils and molecules recognize 16 of 18 extant placental orders. Fossils place the origins of orders around
65 mya as do some molecular studies, but others suggest ordinal diversification as old as 100 mya. Fossil evidence supports a
Laurasian origin for Eutheria (and Metatheria) and Placentalia, although some molecular studies suggest a Gondwanan origin for
both taxa.
2003 Elsevier Science (USA). All rights reserved.
1. Introduction
The oldest eutherian is from 125 mya in China (Ji
et al., 2002) and the oldest metatherians are from
100 mya in North America (Cifelli, 1993). Eutheria and

  

Source: Archibald, J. David - Department of Biology, San Diego State University

 

Collections: Biology and Medicine; Geosciences