Biology Faculty Articles

Title

Placental Mammal Diversification and the Cretaceous-Tertiary Boundary

Document Type

Article

Publication Date

2-4-2003

Publication Title

Proceedings of the National Academy of Sciences of the United States of America

Keywords

Mammalia, Molecular clock, Placentalia, Phylogeny

ISSN

1091-6490

Volume

100

Issue/No.

3

First Page

1056

Last Page

1061

Abstract

Competing hypotheses for the timing of the placental mammal radiation focus on whether extant placental orders originated and diversified before or after the Cretaceous-Tertiary (K/T) boundary. Molecular studies that have addressed this issue suffer from single calibration points, unwarranted assumptions about the molecular clock, and/or taxon sampling that lacks representatives of all placental orders. We investigated this problem using the largest available molecular data set for placental mammals, which includes segments of 19 nuclear and three mitochondrial genes for representatives of all extant placental orders. We used the Thorne/Kishino method, which permits simultaneous constraints from the fossil record and allows rates of molecular evolution to vary on different branches of a phylogenetic tree. Analyses that used different sets of fossil constraints, different priors for the base of Placentalia, and different data partitions all support interordinal divergences in the Cretaceous followed by intraordinal diversification mostly after the K/T boundary. Four placental orders show intraordinal diversification that predates the K/T boundary, but only by an average of 10 million years. In contrast to some molecular studies that date the rat–mouse split as old as 46 million years, our results show improved agreement with the fossil record and place this split at 16–23 million years. To test the hypothesis that molecular estimates of Cretaceous divergence times are an artifact of increased body size subsequent to the K/T boundary, we also performed analyses with a “K/T body size” taxon set. In these analyses, interordinal splits remained in the Cretaceous. _x000D_

Comments

© 2003, The National Academy of Sciences

ORCID ID

0000-0001-7353-8301

ResearcherID

N-1726-2015

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