Downloaded from http://mbe.oxfordjournals.org/ at Pennsylvania StateEditorial University on August 2, 2013 utilize to conclude ons, please ), will solve this McCormack et al. Molecular Biology and Romiguier et al. (2013) ). Considering the current ild phylogenies. This finding Morgan et al. (2013) and

Kumar et al. 2012 Romiguier et al. (2013) Romiguier et al. (2013), on the other hand, Morgan et al. (2013) Murphy et al.). 2007 utinized the largest available genomic data sets Atlantogenata (Song et al. 2012 Both What is the significance of knowing the correct root? First, ews is that all three possibilities are seriously considered. elephants, hyraxes, and tenrecs) and Atlantogenata 2012), whereas coding regionsport with higher GC content sup- their statistical challenges ( puzzle ( concatenate and analyze somemammalian of data the sets largest phylogenomic to date. heterogenous models to account for treegeneity and dataset and hetero- findargue strong that the support “unresolvability”from for the of past Atlantogenata. the use of placental suboptimal They with models root little and stems power. smaller data sets deluge of whole genomedeveloping methods data, like these it to analyze issets heterogeneous correctly data important and, in to some cases, continue fruitful. combining methods may be it may help us understandamong how traits major evolved groups that are ofhave shared placental biogeographic mammals. implications. Second, Theand it fact will afrotherians that are xenarthrans so closely tied to South America and divide their data set into GC- andsupport AT-rich for genes, the analyzing alternate the roots. Theyare show that GC-rich most genes likelyfrom to long-branch support attraction, egregious whereashad topologies AT-rich a and five genic times regions suffer lowersupport error an rate. Afrotherian Interestingly, root, AT-rich whereasAtlantogenata, genes GC-rich leading genes support that the placentalGC-rich rooting genes being conflict usedcould to stems bu explain from why unreliable regions similar of coalescent the analyses genomeserved noncoding supported of elements different different predominantly roots: foundisochores in ultracon- support AT-rich an Afrotherian rooting ( oths and anteater), whereas molecular evolutionists have ty for Molecular Biology and Evolution. All rights reserved. For permissi ; ), ccess publication June 29, 2013 1 ). The Romiguier ; Hedges et al. ,2 , University College Dublin, Dublin, Ireland ) to the molecular ). If we speak of the O’Leary et al. 2013 tate University, University Park Hedges et al. 1996 Wilson and Reeder). 2005 fig. 1 Nishiara et al. 2009 MBE Advance Access published July 27, 2013 27, July published Access Advance MBE ar phylogenetic studies there ome to different conclusions. Morgan et al. 2013 Novacek 1999 ). However, despite the abundance E-mail: [email protected]. and S. Blair Hedges* ). Rather the question is the branching 1 Sudhir Kumar doi:10.1093/molbev/mst118 Advance A Xenarthra). Now, two groups of researchers have scr Xenarthra). Researchers have found this node + mammals, phylogeny, genome, biogeography, evolution. + ) address one such node, the root of the tree of . Needless to say, more research is needed.

Meredith et al. 2011

Twoarticlesinthisissue( The Author 2013. Published by Oxford University Press on behalf of the Socie Department of Biology, Pennsylvania S School of Biology and Environmental Science ß Mol. Biol. Evol. (Afrotheria e-mail: [email protected] favored the two other possible roots: Afrotheria (e.g., Paleontologists favor a root anchored by Xenarthra (e.g., sl Untangling the root of thethat evolutionary only tree three of possibilities placental are mammals seriously has considered. been The nearly bad an n impossible task. The good news is Abstract 2 Mammals Emma C. Teeling 1 Making the Impossible Possible: Rooting the Tree of Placental *Corresponding author: Associate editor: whereas molecular studies haveother equally possibilities: supported an the(Afrotheria two Afrotherian root andto be Atlantogenata one of thelogenetic “hardest” to tree, resolve if in the not mammalian phy- impossible ( Living mammals (~5,500earth species) and exist are considered incally to every diverse be groups biome one of vertebrates of on ( the most phenotypi- and congruence of most molecul The timing ofbased the on splitting event—approximatelyamong molecular 100 Ma clocks—is molecular not evolutionists in debate, ( at least living placental mammals, and c bearingonthequestionandhavecometooppositeconclusions,asreportedinthisissueof Evolution Key words: Approximately 95% ofevolutionary mammals are relationships placentals, havethrough and dozens rapidly of their molecular come analysescades. over By the into any past standard, two focus from the de- the paleontological change view has ofradiation been an with explosive, revolutionary, hoofed post-dinosaur mammals (e.g.,phants) horses, joined cattle, in and a ele- view group of ( deeper origins, reflecting1996; Earth history ( are still major nodes inremain the unresolved molecular and highly tree controversial. of mammals that et al. 2013 Meredith et al. 2011 order of the three major lineages:manatees, afrotherians hyraxes, (e.g., elephants, elephant shrews,xenarthrans aardvarks, and (sloths, tenrecs), anteaters,eoeutherians (all and other placentals; armadillos),root as and the earliest bor- splittingontologists branch with prefer fewest a species, pale- xenarthran root ( hope has been that large phylogenomic studies, despite Teeling and Hedges . doi:10.1093/molbev/mst118 MBE

FIG.1. The root of the evolutionary tree of living placental mammals. (a) Afrotherian root, (b) Xenarthran root, and (c) Atlantogenatan root.

Africa, respectively, continents that separated at about the mammal phylogeny. MolBiolEvol.Advance Access published June Downloaded from same time (~100 Ma) as those groups, is hard to ignore, sug- 29, 2013, doi:10.1093/molbev/mst117. Murphy WJ, Pringle TH, Crider TA, Springer MS, Miller W. 2007. Using gesting that some vicariance was involved regardless of the genomic data to unravel the root of the placental mammal phy- root. If, on the other hand, Afrotheria arose in the New World logeny. Genome Res. 17:413–421. (O’Leary et al. 2013), then the biogeographic story is not as Nishihara H, Maruyama S, Okada N. 2009. Retroposon analysis and simple.Clearly,wehavemoretolearnabouttheearly recent geological data suggest near simultaneous divergence of evolution of placental mammals. the three superorders of mammals. Proc Natl Acad Sci U S A. 106: http://mbe.oxfordjournals.org/ 5235–5240. Novacek MJ. 1999. 100 million years of land vertebrate evolution: the References cretaceous-early tertiary transition. Ann Missouri Bot Garden. 86: Hedges SB, Parker PH, Sibley CG, Kumar S. 1996. Continental breakup 230–258. and the ordinal diversification of birds and mammals. Nature 381: O’Leary MA, Bloch JI, Flynn JJ, et al. (23 co-authors). 2013. The placental 226–229. mammal ancestor and the post-K-Pg radiation of placentals. Science Kumar S, Filipski AJ, Battistuzzi FU, Pond SLK, Tamura K. 2012. Statistics 339:662–667. and truth in phylogenomics. MolBiolEvol.29:457–472. Romiguier J, Ranwez V, Delsuc F, Galtier N, Douzery EJ. 2013. Less is more

McCormack JE, Faircloth BC, Crawford NG, Gowaty PA, Brumfield RT, in mammalian phylogenomics: AT-rich genes minimize tree con- at Pennsylvania State University on August 2, 2013 Glenn TC. 2012. Ultraconserved elements are novel phylogenomic flicts and unravel the root of placental mammals. Mol Biol Evol. markers that resolve placental mammal phylogeny when combined Advance Access published June 29, 2013, doi:10.1093/molbev/ with species tree analysis. Genome Res. 22:746–754. mst116. Meredith RW, Janecka JE, Gatesy J, et al. (22 co-authors). 2011. Impacts Song S, Liu L, Edwards SV, Wu S. 2012. Resolving conflict in eutherian of the cretaceous terrestrial revolution and KPg extinction on mammal phylogeny using phylogenomics and the multispecies mammal diversification. Science 334:521–524. coalescent model. Proc Natl Acad Sci U S A. 109:14942–14947. Morgan C, Foster PG, Webb A, Pisani D, McInerney JO, O’Connell M. Wilson DE, Reeder DM, editors 2005. Mammal species of the world. 2013. Heterogeneous models place the root of the placental Baltimore (MD): Johns Hopkins University Press.

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