Genome Size: A Novel Genomic Signature in Support of Afrotheria Carlo Alberto Redi, 1 Silvia Garagna, 2 Maurizio Zuccotti, 3 Ernesto Capanna 4 1 Fondazione IRCCS Policlinico San Matteo, Pavia, Italy 2 Laboratorio di Biologia dello Sviluppo, Dipartimento di Biologia Animale, Piazza Botta 9, 27100, Pavia, Italy 3 Dipartimento di Medicina Sperimentale, Universitı` di Parma, Parma, Italy 4 Dipartimento di Biologia Animale e dellÕUomo, Universitı` ‘‘La Sapienza’’, Roma, Italy Received: 30 June 2006 / Accepted: 8 January 2007 [Reviewing Editor: Dmitri Petrov] Abstract. Molecular phylogenetic analyses suggest an emerging phylogeny for the extant Placentalia (eutherian) that radically departs from morphologi- cally based constructions of the past. Placental mammals are partitioned into four supraordinal clades: Afrotheria, Xenarthra, Laurasiatheria, and Euarchontoglires. Afrotheria form an endemic Afri- can clade that includes elephant shrews, golden mo- les, tenrecs, aardvarks, hyraxes, elephants, dugongs, and manatees. Datamining databases of genome size (GS) shows that till today just one afrotherian GS has been evaluated, that of the aardvark Orycteropus afer. We show that the GSs of six selected represen- tatives across the Afrotheria supraordinal group are among the highest for the extant Placentalia, pro- viding a novel genomic signature of this enigmatic group. The mean GS value of Afrotheria, 5.3 ± 0.7 pg, is the highest reported for the extant Placentalia. This should assist in planning new genome sequenc- ing initiatives. Key words: Genome size — Mammals — Afrothe- ria — Xenarthra — Laurasiatheria — Euarchon- toglires Introduction Anatomical data (e.g., cranial, postcranial, and den- tal characteristics of extant and fossil mammals) provide evidence for the traditional systematic clas- sification of mammals. In sharp contrast, nucleotide sequences suggest a southern (Gondwana) ancestry for mammals and an evolutionary scheme that par- titions the extant placental (eutherian) mammals into four major supraordinal clades (Hedges 2001; Mad- sen et al. 2001; Murphy et al. 2001): Afrotheria, Xe- narthra, Laurasiatheria, and Euarchontoglires. These groupings result in an odd collection of animals if viewed in light of traditional schemes. Afrotheria is one of the most remarkable hypotheses in mammal evolution: it suggests that nearly one-third of the orders of placental mammals form an endemic Afri- can clade that includes elephant shrews (Macrosceli- dea), golden moles (Chrysochloridae), tenrecs (Tenrecidae), aardvarks (Tubulidentata), hyraxes (Hyracoidea), elephants (Proboscidea), and the dug- ongs and manatees (Sirenia). The possibility that afrotherian animals were re- lated was first recognized by de Jong et al. (1981), who proposed that elephant, hyrax, aardvark, and elephant shrew form a monophyletic group by determining aA-crystallin protein sequences of sev- eral mammalian species. There are a few identified genomic changes in support of Afrotheria including the detection of a unique 9-bp deletion in exon 11 of the BRCA1 gene (Madsen et al. 2001), the protein sequence signatures (‘‘protein-morphological syna- pomorphies’’) detected by van Dijk et al. (2001), the Correspondence to: Carlo Alberto Redi; email: carloalberto.redi@ unipv.it J Mol Evol (2007) 64:484–487 DOI: 10.1007/s00239-006-0237-1