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Journal of Mammalian Evolution, Vol. 8, No. 2, 2001 1064-7554/01/0600-0107$19.50/0 2001 Plenum Publishing Corporation
 

Summary: Journal of Mammalian Evolution, Vol. 8, No. 2, 2001
1064-7554/01/0600-0107$19.50/0 2001 Plenum Publishing Corporation
107
Quantitative Analysis of the Timing of the Origin and
Diversification of Extant Placental Orders
J. David Archibald1,2 and Douglas H. Deutschman1
Fossil evidence is consistent with origination and diversification of extant placental orders in
the early Tertiary (Explosive Model), and with the possibility of some orders having stem
taxa extending into the Cretaceous (Long Fuse Model). Fossil evidence that 15 of 18 extant
placental orders appeared and began diversification in the first 16 m.y. of the Cenozoic is,
however, at odds with molecular studies arguing some orders diversified up to 40 m.y. earlier
in the Early Cretaceous (Short Fuse Model). The quality of the fossil record was assessed by
tabulating localities of all mammals in the last 105 m.y. Global locality data (except Africa)
for 105 m.y. of eutherian evolution indicate discernible biogeographic patterns by the last 15
m.y. of the Cretaceous. Eutherian genera increase from 11 in latest Cretaceous to 139 in earliest
Tertiary, although both are represented by about 50 localities. Yet even in the Late Cretaceous
of North America and Asia where eutherians are abundant, none of the 18 extant orders are
definitely known. A series of Monte Carlo simulations test whether the rapid appearance of most
mammalian orders is statistically significant, and if so, whether it is a radiation event or an artifact
of a limited fossil record. Monte Carlo tests affirm that the clustering of appearances in the early

  

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

 

Collections: Biology and Medicine; Geosciences