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Phylogeny and Relationships of Taeniodonta, an Enigmatic Order of Eutherian Mammals (Paleogene, North America)

出版	Ohio State University, 2009
URL	http://books.google.com.hk/books?id=MBkzngAACAAJ&hl=&source=gbs_api

註釋Abstract: The Taeniodonta is group of eutherian mammals from the Paleogene of North America, whose exact place in eutherian phylogeny is uncertain. Taeniodonts evolved rapidly in the Paleocene to achieve, in some forms, large body size, hypselodont (i.e., evergrowing) canine and postcanine teeth, and peculiar patterns of tooth wear. Eleven genera of taeniodonts occur in two main subclades, recognized at the level of families or subfamilies depending on author, the Conoryctidae and the Stylinodontidae. The conoryctids were smaller, probably insectivorous or omnivorous, and retained a larger number of primitive characters than did the stylinodontids. The stylinodontids were larger than the conoryctids, possessed massive canines, and exhibit a trend toward hypselodonty of the canines and molars. Prior to this study, there has not been a comprehensive phylogeny of all of the currently recognized genera of taeniodonts. I take up the relations of genera of taeniodonts to one another and overall biogeographic history. I performed cladistic analyses using NONA and Winclada to determine the evolutionary relations of the known genera of the Taeniodonta. Two clades are well supported, a clade consisting of the conoryctids exclusive of Onychodectes (i.e., Conoryctella, Conoryctes, and Huerfanodon) and a clade consisting of all the known stylinodontids (Wortmania, Schochia, Psittacotherium, Ectoganus, and Stylinodon). Stratocladistic analysis, which takes into account the temporal sequence of taxa in the fossil record, supports the results of phylogenetic analysis using morphological characters alone. Phylogenetic, stratigraphic, and geographic data contribute to reconstructing the biogeographical history of the taeniodonts. In these analyses, the Late Cretaceous taeniodont Schowalteria occupies the most basal position in taeniodont phylogeny, pre-dating an inferred conoryctid-stylinodontid split in the early Paleocene. I investigate the higher-level relations and ancestry of the taeniodonts as well as the monophyletic or diphyletic origins. I describe a newly discovered fossil lower jaw from the early Paleocene of North Dakota that I interpret to be the lower jaw of Alveugena, a taxon previously argued to be a transitional form between cimolestids and the taeniodonts. This discovery contributes new characters and facilitates study of the relations between taeniodonts and basal cimolestans. This study corroborates the hypothesis that Alveugena is the sister taxon of the taeniodonts. Contrary to earlier analyses, the Late Cretaceous-Paleocene Cimolestes is found to be the sister taxon of Alveugena+Taeniodonta rather than the Paleocene Procerberus, thought by some to be closer to the taeniodonts. Stratocladistics provided additional support for the conclusions of the analyses of morphology alone and implicate Cimolestes as a possible ancestor to Alveugena and the taeniodonts. Further cladistic analyses including taeniodonts, Late Cretaceous stem eutherians, and Paleogene representatives of crown eutherian clades constrain the higher-level relations of taeniodonts. This study shows that the taeniodonts lack the synapomorphies that link crown eutherians together. I also discuss the evolutionary rates of the canine and molar evolution in the group, and rediagnose the clades. In conclusion, the taeniodonts are a monophyletic group of stem eutherian mammals whose closest known sister group is Alveugena, and most likely Cimolestes gave rise to the Alveugena and the taeniodonts.