To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.

No abstract

The Eocene-Oligocene boundary (EOB) marks a period of dramatic global climatic change correlated with pronounced mammalian faunal change. The timing of these events is well constrained in North America and Europe, but the Asian record has yet to produce a synthetic section linking environmental change, mammalian fossils, and precise geochronological dates. Here we present the fi rst magnetostratigraphic section for the Hsanda Gol Formation, Mongolia, which yields signifi cant Oligocene fossils and also marks a pattern of aridifi cation that is tightly correlated to the EOB (33.9 Ma), supporting a broader pattern of aridifi cation in the central Asian plateau across the EOB. Oligocene faunas of Asia can now be confi dently correlated to those of North America, Europe, and Africa. These results suggest that mammalian faunal turnover within Asia occurred slightly later than similar events within Europe, and question the infl uence of Asian immigrants on the Grande Coupure faunal turnover. of equipment and discussion. Gary Scott (BGC), Gilberto Mello (formerly at LDEO), Linda Sohl (Columbia University), and Peter LeTourneau (Wesleyan University) provided helpful discussions. The Paleontological Centre of the Mongolian Academy of Sciences, in particular R. Barsbold and D. Badamgarav, are acknowledged for their support. Faysal Bibi (Yale University), Odsurengiin Batulzii, Marc Carrasco, and Bolortsetseg Minjin helped with fi eld work. The

Many living vertebrates exhibit complex social structures, evidence for the antiquity of which is limited to rare and exceptional fossil finds. Living elephants possess a characteristic social structure that is sex-segregated and multi-tiered, centred around a matriarchal family and solitary or loosely associated groups of adult males. Although the fossil record of Proboscidea is extensive, the origin and evolution of social structure in this clade is virtually unknown. Here, we present imagery and analyses of an extensive late Miocene fossil trackway site from the United Arab Emirates. The site of Mleisa 1 preserves exceptionally long trackways of a herd of at least 13 individuals of varying size transected by that of a single large individual, indicating the presence of both herding and solitary social modes. Trackway stride lengths and resulting body mass estimates indicate that the solitary individual was also the largest and therefore most likely a male. Sexual determination for the herd is equivocal, but the body size profile and number of individuals are commensurate with those of a modern elephant family unit. The Mleisa 1 trackways provide direct evidence for the antiquity of characteristic and complex social structure in Proboscidea.