a new basal caniform (mammalia carnivora) from the middle eocene of north america and remarks on the phylogeny of early carnivorans一个新的基底caniform(哺乳纲食肉类)中始新世的北美和评价早期食肉的发展史.pdfVIP

A New Basal Caniform (Mammalia: Carnivora) from the Middle Eocene of North America and Remarks on the Phylogeny of Early Carnivorans Susumu Tomiya* Museum of Paleontology, Museum of Vertebrate Zoology, and Department of Integrative Biology, University of California, Berkeley, California, United States of America Abstract Background: Despite a long history of research, the phylogenetic origin and initial diversification of the mammalian crown- group Carnivora remain elusive. Well-preserved fossil materials of basal carnivorans are essential for resolving these issues, and for constraining the timing of the carnivoran origin, which constitutes an important time-calibration point in mammalian phylogenetics. Methodology/Principal Findings: A new carnivoramorphan from the middle Eocene of southern California, Lycophocyon hutchisoni, is described. The new taxon exhibits stages of dental and basicranial evolution that are intermediate between earlier carnivoramorphans and the earliest representatives of canoid carnivorans. The evolutionary affinity of the new taxon was determined by a cladistic analysis of previously-published and newly-acquired morphological data for 30 Paleogene carnivoramorphans. The most-parsimonious trees identified L. hutchisoni as a basal caniform carnivoran, and placed (1) Tapocyon robustus, Quercygale angustidens, ‘‘Miacis’’ sylvestris, ‘‘M.’’ uintensis, and ‘‘M.’’ gracilis inside or outside the Carnivora, (2) nimravids within the Feliformia, and (3) the amphicyonid Daphoenus outside the crown-group Canoidea. Parsimony reconstructions of ancestral character states suggest that loss of the upper third molars and development of well-ossified entotympanics that are firmly fused to the basicranium (neither condition is observed in L. hutchisoni) are not associated with