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Mammals are the most encephalized vertebrates, with the largest brains relative to body size. Placental mammals have particularly enlarged brains, with expanded neocortices for sensory integration, the origins of which are unclear. We used computed tomography scans of newly discovered Paleocene fossils to show that contrary to the convention that mammal brains have steadily enlarged over time, early placentals initially decreased their relative brain sizes because body mass increased at a faster rate. Later in the Eocene, multiple crown lineages independently acquired highly encephalized brains through marked growth in sensory regions. We argue that the placental radiation initially emphasized increases in body size as extinction survivors filled vacant niches. Brains eventually became larger as ecosystems saturated and competition intensified.

The middle Eocene Washakie Formation of Wyoming, USA, provides a rare window, within a single depositional basin, into the faunal transition that followed the early Eocene warming events. Based on extensive examination, we report a minimum of 27 species of carnivorous mammals from this formation, more than doubling the previous taxic count. Included in this revised list are a new species of carnivoraform, Neovulpavus mccarrolli n. sp., and up to ten other possibly new taxa. Our cladistic analysis of early Carnivoraformes incorporating new data clarified the array of middle Eocene taxa that are closely related to crown-group Carnivora. These anatomically relatively derived carnivoraforms collectively had an intercontinental distribution in North America and east Asia, exhibiting notable variations in body size and dental adaptation. This time period also saw parallel trends of increase in body size and dental sectoriality in distantly related lineages of carnivores spanning a wide range of body sizes. A new, model-based Bayesian analysis of diversity dynamics accounting for imperfect detection revealed a high probability of substantial loss of carnivore species between the late Bridgerian and early Uintan North American Land Mammal 'Ages', coinciding with the disappearance of formerly common mammals such as hyopsodontids and adapiform primates. Concomitant with this decline in carnivore diversity, the Washakie vertebrate fauna underwent significant disintegration, as measured by patterns of coordinated detection of taxa at the locality level. These observations are consistent with a major biomic transition in the region in response to climatically induced opening-up of forested habitats. UUID: http://zoobank.org/9162f1a6-a12c-4d55-ba1d-dc66e8cda261

The name “Cetartiodactyla” was proposed in 1997 to reflect the molecular data that suggested that Cetacea is closely related to Artiodactyla. Since then, that taxon has spread in popularity, even outside the scientific literature. However, the implications of the name are confusing, because Cetacea and Artiodactyla are not sister-taxa. Instead, the evidence clearly shows that cetaceans are a group embedded within Artiodactyla, not a sister-taxon of equal rank. It has long been accepted practice that systematists do not modify the names of higher groups when new subgroups are added to them. For example, Owen’s original concept of Artiodactyla did not change its name when more and more disparate taxa were added to it. Dinosauria did not become “Avedinosauria” when it became clear that birds are a subgroup of dinosaurs, nor did Reptilia become “Avereptilia”. In the interests of taxonomic priority and stability, and especially because the name is inherently misleading, we recommend that the name “Cetartiodactyla” be abandoned. If one wishes to make a reference to the fact that whales are now considered to be a subgroup of artiodactyls, they could be referred to informally as “whales and other artiodactyls” or “whales and terrestrial artiodactyls” without using a formal taxonomic name that is confusing and misleading.

Abstract Cranial skeletal material of the Eocene palaeanodont Metacheiromys marshi was examined using high-resolution CT scans. The present study represents the first time that CT scans have been conducted on skulls of this extinct fossorial mammal. The bony osteology of the auditory region is described in detail, including the ectotympanic and entotympanic, the petrosal in both tympanic and endocranial views, and the middle ear ossicles. The results of this investigation confirm a number of derived resemblances between palaeanodonts and xenarthrans, including a large entotympanic element in the medial wall of the auditory bulla, the presence of an anteroventral process of the tegmen tympani, and a posttemporal canal. However, the present study also provides novel derived auditory features linking palaeanodonts and pangolins, consistent with current understanding of palaeanodont phylogenetic relationships, including the absence of an ectotympanic styliform process, a posterolaterally oriented aperture to the cochlear fossula, and a convex mallear head / concave incudal head. Several autapomorphic features characterizing the auditory osteology of Metacheiromys are also noted. The presence of a large, spherical mallear head, and of a capacious tympanic cavity extended into sinuses in surrounding bones, likely represent adaptations for fossoriality, consistent with palaeobiological inferences drawn from the postcranial anatomy of Metacheiromys.

The Cenozoic radiation of mammals was a profound moment in vertebrate evolution, however, many aspects of this radiation remain poorly understood, largely because phylogenetic and macroevolutionary studies have ignored mammals from the Paleocene.In order to address this deficit, we are building a comprehensive higher-level phylogeny using anatomical and genetic data of a large number of mammalian taxa (both extinct and extant).This phylogeny will include an unprecedented number of Paleocene taxa, including many enigmatic forms that have formerly been relegated to "wastebasket" groups.This project will incorporate a wealth of fossil specimens that have been collected from the Paleocene Nacimiento Formation of the San Juan Basin, northwestern New Mexico.The Nacimiento Formation contains the longest and most complete record of mammalian succession through the early Paleocene.Moreover, many extraordinary specimens have been amassed from these deposits, especially over the last 2-3 decades, through focused collecting efforts by the New Mexico Museum of Natural History and Science.These fossils are being studied using a variety of new techniques, including high-resolution CT scanning, that are revealing new details of the anatomy and functional morphology, that are bringing new insights into the biology and evolution of these archaic animals.Preliminary results of our comprehensive phylogeny of Paleocene mammals build upon previous large datasets, including most Paleocene lineages -(262 taxa [58 extant and 204 extinct]) scored for over 2,000 morphological characters.Molecular data from the extant taxa, over 35,000 base pairs from 26 nuclear genes will ultimately also be included.These results are based on use of maximum parsimony, but later analyses will also use maximum likelihood and Bayesian methodology.Our preliminary results find that most Paleocene taxa are found to be stem members of major extant clades (e.g., Primates, Afrotheria, Laurasiatheria, Carnivoramorpha, Euungulata).When coupled with high-resolution geochronological record being developed from the Nacimiento Formation record, our analyses show that many major mammalian clades originated very early in the Paleogene.

A partial petrosal from the Upper Jurassic Morrison Formation of the Fruita Paleontological Area of western Colorado preserving the pars cochlearis and part of the pars canalicularis is described. The endocast of the inner ear showing the cochlea, vestibule, lateral semicircular canal, and the terminal ends of the anterior and posterior semicircular canals is reconstructed from mu CT scans. This specimen is only the fourth petrosal known from the Morrison Formation. Mammals known from Fruita include Fruitafossor windsheffeli Luo and Wible, 2005, the triconodontid Priacodon fruitaensis Rasmussen and Callison, 1981, the plagiaulacoid multituberculate Glirodon grandis Engelmann and Callison, 1999, and unnamed spalacotheriids and dryolestoids. The partial petrosal and its endocast share significant features with dryolestoids from the Upper Jurassic of Guimarota, Portugal, including a separate fenestra cochleae and cochlear canaliculus, and a cochlea that is coiled more than 200 degrees. In light of these similarities, the Fruita petrosal is assigned to Dryolestoidea.

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 external and endocranial surfaces of the skull of the African palm civet, Nandinia binotata (Gray, 1830), are described and illustrated in detail based on 30 specimens (from Carnegie Museum of Natural History and American Museum of Natural History). With the inclusion of a newborn and six juveniles with deciduous dentitions, a reasonable ontogenetic series is represented. The bone-by-bone descriptions are primarily based on the condition in an adult female and the newborn with consideration of variation across the sample. The principal cranial foramina are treated in a glossary, and the hyoid apparatus and larynx are described from a single specimen. The sample exhibits a remarkable degree of variability in cranial features that are often used as different states of characters in phylogenetic analysis (e.g., number and position of palatal foramina, the orbital mosaic, and composition of the lacrimal foramen).Nandinia binotata, the only taxon in the Nandiniidae, has been identified as the most basal extant feliform in recent phylogenetic analyses of both molecular and morphological data. It has long been recognized that its ear region with its uninflated auditory bulla exhibits a primitive level of organization. To assess the primitive nature of the skull of N. binotata, comparisons are made with three extant carnivorans, the felid Felis catus Linnaeus, 1758, the viverrid Genetta genetta (Linnaeus, 1758), and the canid Canis lupus Linnaeus, 1758. Of the three, N. binotata shares numerous resemblances across the skull with G. genetta, which accounts for its historical inclusion in the Viverridae. Whereas aspects of the ear region of N. binotata are clearly unique among extant carnivorans, the rest of its skull is not similarly so.

Previous analyses of the mammalian clade Carnivoramorpha have tended to sample only cranial and dental character systems, particularly those that included early Cenozoic taxa, Viverravidae and basal Carnivoraformes (the latter being a paraphyletic array of taxa traditionally referred to as the ‘Miacidae’). In this study we add more than 100 postcranial characters to an existing dataset dominated by cranio-dental characters. The addition of the new characters permits the inclusion of a large number of basal carnivoraforms, known solely or predominantly from postcranial characters, that previously would have been ‘unplaceable’ in a phylogenetic analysis. The resultant phylogeny recovers most of the same clades identified in previous studies, but resolves some relationships differently within the basal carnivoraforms. A novel (unnamed) monophyletic subclade of the Carnivoraformes is recovered, supported in part by characters from both the prior and new datasets. The inclusion of a substantial suite of postcranial characters expands the ability to assess the relationships of basal carnivoramorphan taxa, and permits the inclusion of many taxa represented only by incomplete material.

Authoritative anatomical references depict domestic dogs and cats as having a malleus with a short rostral (anterior) process that is connected via a ligament to the ectotympanic of the auditory bulla. Similar mallei have been reported for representatives of each of the 15 extant families of Carnivora, the placental order containing dogs and cats. This morphology is in contrast to a malleus with a long rostral process anchored to the ectotympanic that is considered to be primitive for mammals. Our reexamination of extant carnivorans found representatives from 12 families that possess an elongate rostral process anchored to the ectotympanic. Consequently, the malleus also is a component of the bulla. In a subset of our carnivoran sample, we confirmed that the elongate rostral process on the ectotympanic is continuous with the rest of the malleus through a thin osseous lamina. This morphology is reconstructed as primitive for Carnivora. Prior inaccurate descriptions of the taxa in our sample having mallei continuous with the bulla were based on damaged mallei. In addition to coupling to the ectotympanic, the rostral process of the malleus was found to have a hook-like process that fits in a facet on the skull base in representatives from seven families (felids, nandiniids, viverrids, canids, ursids, procyonids, and mustelids); its occurrence in the remaining families could not be ascertained. This feature is named herein the mallear hook and is likewise reconstructed to be primitive for Carnivora. We also investigated mallei in one additional placental order reported to have mallei not connected to the ectotympanic, Pholidota (pangolins), the extant sister group of Carnivora. We found pholidotans to also have anchored mallei with long rostral processes, but lacking mallear hooks. In light of our results, other mammals previously reported to have short rostral processes should be reexamined.

A new genus and species of basal non-Viverravidae Carnivoramorpha, Dawsonicyon isami, is named and described. This new taxon is based upon DMNH 19585, an almost complete skeleton, which was collected from the Black's Fork Member (informal 'Bridger B' subunit) of the Bridger Formation in southwestern Wyoming, USA. The specimen is incorporated into an existing craniodental data matrix, and the associated phylogenetic analyses support the identification of this species as a new basal carnivoramorphan. This new taxon is dentally compared to all known genera of non-viverravid basal carnivoramorphans, as well as with all known species of the problematic genus Miacis. Postcrania are compared in detail with other described specimens of non-viverravid basal carnivoramorphans and more generally with known postcrania of viverravids. Preliminary functional interpretations of a scansorial locomotor mode are offered for this new taxon. Its implications for the diversity of middle Eocene basal carnivoramorphans is briefly discussed, including expansion of the already high diversity in the Black's Fork Member of the Bridger Formation (at least 11 species in 8 genera).

Cetaceans are remarkable among mammals for their numerous adaptations to an entirely aquatic existence, yet many aspects of their phylogeny remain unresolved. Here we merged 37 new sequences from the nuclear genes RAG1 and PRM1 with most published molecular data for the group (45 nuclear loci, transposons, mitochondrial genomes), and generated a supermatrix consisting of 42,335 characters. The great majority of these data have never been combined. Model-based analyses of the supermatrix produced a solid, consistent phylogenetic hypothesis for 87 cetacean species. Bayesian analyses corroborated odontocete (toothed whale) monophyly, stabilized basal odontocete relationships, and completely resolved branching events within Mysticeti (baleen whales) as well as the problematic speciose clade Delphinidae (oceanic dolphins). Only limited conflicts relative to maximum likelihood results were recorded, and discrepancies found in parsimony trees were very weakly supported. We utilized the Bayesian supermatrix tree to estimate divergence dates among lineages using relaxed-clock methods. Divergence estimates revealed rapid branching of basal odontocete lineages near the Eocene-Oligocene boundary, the antiquity of river dolphin lineages, a Late Miocene radiation of balaenopteroid mysticetes, and a recent rapid radiation of Delphinidae beginning approximately 10 million years ago. Our comprehensive, time-calibrated tree provides a powerful evolutionary tool for broad-scale comparative studies of Cetacea.

This paper provides the first detailed description of the only known postcranial skeletal elements of "Miacis" uintensis. The morphology of the skeleton differs markedly from previously described "miacids" (a paraphyletic assemblage of early fossil carnivoramorphans), invalidating the notion that all "miacids" were very similar in their postcranial morphology and locomotor styles. The majority of the differences indicate an animal less well adapted to an arboreal lifestyle than has been inferred for other early "miacid" carnivoramorphans. A phylogenetic analysis clearly nests "Miacis" uintensis within the paraphyletic array of taxa previously referred to as the "Miacidae," in a position closer to the crown clade Carnivora than is Vulpavus, a "miacid" whose postcranium has been previously described. When compared with the early canid Hesperocyon, this specimen shares many features thought to relate to the acquisition of a more terrestrial mode of life. This result indicates that, in contrast to prior models suggesting arboreality for all "miacids," at least one independent 'descent from the trees' occurred much earlier within the array of stem carnivoramorphan taxa.