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.

The semicircular canal system of vertebrates helps coordinate body movements, including stabilization of gaze during locomotion. Quantitative phylogenetically informed analysis of the radius of curvature of the three semicircular canals in 91 extant and recently extinct primate species and 119 other mammalian taxa provide support for the hypothesis that canal size varies in relation to the jerkiness of head motion during locomotion. Primate and other mammalian species studied here that are agile and have fast, jerky locomotion have significantly larger canals relative to body mass than those that move more cautiously.generalized least-squares analysis ͉ mammals ͉ vestibular system

Plesiadapiforms are central to studies of the origin and evolution of primates and other euarchontan mammals (tree shrews and flying lemurs). We report results from a comprehensive cladistic analysis using cranial, postcranial, and dental evidence including data from recently discovered Paleocene plesiadapiform skeletons (Ignacius clarkforkensis sp. nov.; Dryomomys szalayi, gen. et sp. nov.), and the most plesiomorphic extant tree shrew, Ptilocercus lowii. Our results, based on the fossil record, unambiguously place plesiadapiforms with Euprimates and indicate that the divergence of Primates (sensu lato) from other euarchontans likely occurred before or just after the Cretaceous/Tertiary boundary (65 Mya), notably later than logistical model and molecular estimates. Anatomical features associated with specialized pedal grasping (including a nail on the hallux) and a petrosal bulla likely evolved in the common ancestor of Plesiadapoidea and Euprimates (Euprimateformes) by 62 Mya in either Asia or North America. Our results are consistent with those from recent molecular analyses that group Dermoptera with Scandentia. We find no evidence to support the hypothesis that any plesiadapiforms were mitten-gliders or closely related to Dermoptera.Euarchonta ͉ phylogeny ͉ Paromomyidae ͉ Micromomyidae ͉ Paleogene T he origin of Primates represents the first clear step in the divergence of humans from the rest of Mammalia, yet our understanding of this important period in evolutionary history remains limited. The systematic relationships of Paleocene-Eocene plesiadapiforms, which have been considered the ancestors of either Euprimates (primates of ''modern aspect'' or crown-clade primates) (1, 2) or of Dermoptera (3, 4) continue to be debated. Clarifying the position of plesiadapiforms is central to understanding the broader relationships among euarchontan mammals (Primates, Scandentia, Dermoptera), and to testing adaptive hypotheses of primate origins (5, 6) by using direct evidence from the fossil record.Plesiadapiforms are among the most diverse and well sampled Paleogene mammal groups, with Ͼ120 species classified into 11 or 12 families from the Paleocene and Eocene of North America, Europe, Asia, and possibly Africa (7,8). The plesiadapiform dental record is extremely diverse, suggesting correlated diversity in diet and behavior; however, comparatively little is known about the cranial or postcranial morphology of plesiadapiforms [see supporting information (SI) Text, Part 1]. Well preserved crania have been documented for only three families: Plesiadapidae, Microsyopidae, and Paromomyidae (1, 9-11). Postcrania are known from a taxonomically limited sample of North American and European plesiadapids (1), from a sample of North American paromomyids and micromomyids (3, 4, 12) the identification and associations of which are still controversial (13,14), from a recently published North American carpolestid skeleton (15, 16), and from a few other isolated and questionably identified elements (7,17,18). Following the sugges...

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