Previous analyses of relations, divergence times, and diversification patterns among extant mammalian families have relied on supertree methods and local molecular clocks. We constructed a molecular supermatrix for mammalian families and analyzed these data with likelihood-based methods and relaxed molecular clocks. Phylogenetic analyses resulted in a robust phylogeny with better resolution than phylogenies from supertree methods. Relaxed clock analyses support the long-fuse model of diversification and highlight the importance of including multiple fossil calibrations that are spread across the tree. Molecular time trees and diversification analyses suggest important roles for the Cretaceous Terrestrial Revolution and Cretaceous-Paleogene (KPg) mass extinction in opening up ecospace that promoted interordinal and intraordinal diversification, respectively. By contrast, diversification analyses provide no support for the hypothesis concerning the delayed rise of present-day mammals during the Eocene Period.

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.

We present a revised Cenozoic geochronology based upon a bestfit to selected high-temperature radiometric dates on a number of identified magnetic polarity chrons (within the Late Cretaceous, Paleogene, and Neogene) which minimizes apparent accelerations in seafloor spreading. An assessment of >200 first-order correlations of calcareous plankton biostratigraphic datum events to magnetic polarity stratigraphy yields an improved correlation of the standard magnetostratigraphic, standard biostratigraphic (zonal) and chronostratigraphic boundaries, as well as improved resolution in marinecontinental stratigraphic correlations. The time scale presented here has been accepted by the Committee on Geochronology as the standard time scale for the Cenozoic for the Decade of North American Geology (DNAG).

S U M M A R Y :We present a revised Paleogene geochronology based upon a best fit to selected high temperature radiometric dates on a number of identified magnetic polarity chrons (within the late Cretaceous, Paleogene and Neogene) which minimizes apparent accelerations in sea-floor spreading. An assessment of first order correlations of calcareous plankton biostratigraphic datum events to magnetic polarity stratigraphy yields the following estimated magnetobiochronology of major chronostratigraphic boundaries: Cretaceous-Tertiary boundary (Chron C29R), 66.4 Ma; Paleocene-Eocene (Chron C24R), 57.8 Ma; Eocene-Oligocene (Chron C13R), 36.6 Ma; Oligocene-Miocene (Chron C6CN), 23.7 Ma.The Eocene is seen to have expanded chronologically (-21 m.y.) at the expense of the Paleocene (-9 m.y.) and is indeed the longest of the Cenozoic epochs. In addition, magnetobiostratigraphic correlations require adjustments in apparent correlations with standard marine stage boundaries in some cases (particularly in the Oligocene). Finally, we present a correlation between standard Paleogene marine and terrestrial stratigraphies.It is nearly 20 years since Brian Funnell prepared the first relatively precise Cenozoic time-scale based on an assessment of palaeontologically controlled radiometric data in connection with the symposium on the Phanerozoic timescale sponsored by the London Geological Society, and 10 years since one of us (WAB) presented the first in a series of attempts to further refine Cenozoic geochronology. During the past decade several revisions to the Cenozoic time-scale have appeared and here, at this, the second symposium on the Phanerozoic time-scale sponsored by the Geological Society of London, it is appropriate to present an updated and, hopefully, improved version of the Cenozoic time-scale.It is opportune that over the past decade direct correlation has been achieved between plankton biostratigraphy in some of the standard European continental marine sections and North American terrestrial vertebrate biochronology and magnetic polarity stratigraphy over much of the Cenozoic Era. The recent improvement in deep sea coring techniques has further extended these correlations on a global scale. It is now possible to make age estimates of epoch boundaries and the extent of time-stratigraphic (standard ages) units in terms of plankton biostratigraphy and magnetic polarity chrons and/or anomalies.Finally a critical evaluation must be made within a geohistorical context of biostratigraphically controlled radiometric dates and radiometrically dated polarity stratigraphy in order to provide constraints on an internally consistent geologic time-scale.The revised Cenozoic geochronology has been prepared in two parts: (a) Paleogene; (b) Neogene. In this paper dealing with the Paleogene we first discuss the development of geomagnetic polarity history of the late Cretaceous and Cenozoic. A revised geochronology is then presented which is based upon a best fit to selected high temperature radiometric dates on a number of identifi...