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Mammal Madness: Is the Mammal Tree of Life Not Yet Resolved?

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Review

Mammal Madness: Is the Mammal Tree of Life Not Yet Resolved?

Nicole M Foley et al. Philos Trans R Soc Lond B Biol Sci.

Abstract

Most molecular phylogenetic studies place all placental mammals into four superordinal groups, Laurasiatheria (e.g. dogs, bats, whales), Euarchontoglires (e.g. humans, rodents, colugos), Xenarthra (e.g. armadillos, anteaters) and Afrotheria (e.g. elephants, sea cows, tenrecs), and estimate that these clades last shared a common ancestor 90-110 million years ago. This phylogeny has provided a framework for numerous functional and comparative studies. Despite the high level of congruence among most molecular studies, questions still remain regarding the position and divergence time of the root of placental mammals, and certain 'hard nodes' such as the Laurasiatheria polytomy and Paenungulata that seem impossible to resolve. Here, we explore recent consensus and conflict among mammalian phylogenetic studies and explore the reasons for the remaining conflicts. The question of whether the mammal tree of life is or can be ever resolved is also addressed.This article is part of the themed issue 'Dating species divergences using rocks and clocks'.

Keywords: coalesence; fossils; molecules; phylogenomics; supermatrix; time-tree.

Figures

Figure 1.
Figure 1.
Timetree based on mcmctree supports a long fuse model of mammalian diversification [4,5]. Divergence time estimates were obtained under a GTR + Γ model of sequence evolution, 99 calibrated nodes (see electronic supplementary material table S2 for details), and autocorrelated rates of evolution. Divergence time estimates for clades of interest are shown at each node, with the 95% CI denoted by blue bars. The dataset included 26 tree of life gene fragments [4] and was expanded to include 286 taxa (see electronic supplementary material, table S1 for taxa, gene fragments and accession numbers). GenBank sequences for single genes were supplemented with available genome data that were mined using BLAST searches. The tree was estimated using RAxML [99] on the CIPRES web server [100] under a fully partitioned model where each partition had its own GTR + Γ model of sequence evolution. Paintings by Carl Buell. (Online version in colour.)

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