O'LEARY, M. A., BLOCH,  J. I., FLYNN, J. J., GAUDIN, T. J.,  GIALLOMBARDO, A.,  GIANNINI, N. P., GOLDBERG, S. L.,  KRAATZ, B. P.,  LUO, Z.-X., MENG, J., NI, X., NOVACEK, M. J PERINI, F. A., RANDALL, Z. S., ROUGIER, G. W., SARGIS, E. J., SILCOX, M. T., SIMMONS, N. B., SPAULDING, M., VELAZCO, P. M., WEKSLER, M., WIBLE, J. R. & CIRRANELLO, A. L. (2013)

The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals. 

Science (08 Feb 2013) 339 (6120): 662-667.
DOI: 10.1126/science.1229237

Abstract:

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.