The morphology of Tribosphenomys (rodentiaformes, mammalia): Phylogenetic implications for basal Glires

We provide the first full description of the rodentiaform Tribosphenomys minutus from the late Paleocene Bayan Ulan locality of Inner Mongolia, China. All material presently referable to the taxon is treated, including the holotype plus more recently discovered teeth, jaws, and postcranial elements. To elucidate the phylogenetic placement of Tribosphenomys, a suite of 82 osteological characters across 36 terminal taxa was sampled and analyzed. A data matrix was generated and subjected to phylogenetic analyses using parsimony. The results of the analyses confirm the outgroup placement of Tribosphenomys relative to Rodentia (in the crown-clade restricted sense of that name). Other results include a sister-group pairing of lagomorphs and rodents (Glires), with various extinct taxa interposed as sequential outgroups to each of these crown clades. The phylogenetic definitions of names attaching to major clades of gliroid mammals are reviewed, with new ones being proposed. © 2001 Plenum Publishing Corporation.