CHEWING PATTERN COMPARISON AND ANALYSES AMONG NEOPLAGIAULACIDAE, PTILODONTIDAE, EUCOSMODONTIDAE, AND MICROCOSMODONTIDAE (MULTITUBERCULATA, MAMMALIA)

Multituberculates belong to an extinct mammalian group which lived from at least the late Jurassic to the late Eocene. Cimolodonta is a monophyletic group which includes nearly all Late Cretaceous and Paleogene multituberculates. Multituberculates are distinguished by a pair of blade-like tooth which were the upper and lower fourth premolar (P4 and p4, respectively). Based on the tooth wear pattern left on P4’s and p4’s, the chewing pattern of multituberculates could be reconstructed. Among all multituberculates, only the chewing pattern of Ptilodus was studied in details. Since then it has been common practice to treat the chewing pattern of Ptilodus as the representative of all multituberculates.

In this project, the wearing patterns on P4’s and p4’s have been studies and compared in details among the families of Neoplagiaulacidae, Ptilodontidae, Eucosmodontidae, and Microcosmodontidae, the major members of Cimolondonta which possess a pair of blade-like tooth. It has been found that differing from what were widely assumed, there are diversified chewing patterns among these multituberculate families. Because of the universally distributed apical wear on p4’s of Ptilodontidae, all of the members of Ptilodontidae use crushing as the major chewing mode, which agrees with the previous study on Ptilodus, the best studied genus of Ptilodontidae. For Neoplagiaulacidae, the postero-labial wear rather that the apical wear on p4’s are universally distributed, and shearing rather than crushing is the major chewing mode for all members in this family. For Eucosmodontidae and Microcosmodontidae, both kind of tooth wear are presented and thus both shearing and crushing are used for members of these two families. The morphological difference of p4’s and P4’s are also compared and the result agrees with that from the tooth wear comparison.

A phylogenetic analysis has been conducted to trace the evolutionary history of the chewing patterns within Neoplagiaulacidae, Ptilodontidae, Eucosmodontidae, and Microcosmodontidae, including representative taxa from each family and outgroup. The result shows that the shearing mode is the plesiomorphic chewing mode of multituberculates, and the crushing mode evolved convergently between Ptilodontidae and the lineage of Eucosmodontidae and Microcosmodontidae.