Origin of Mammalia: The craniodental evidence reexamined

Publisher Website
Google Scholar
Abstract
In Rowe (1988), 158 characters of the skull and postcranial skeleton distributed among Placentalia, Marsupialia, Monotremata, Multituberculata, Morganucodontidae, Tritylodontidae, and Exaeretodon were analyzed with PAUP. Mammalia, defined by Rowe as comprising the most recent common ancestor of living monotremes, marsupials, and placentals, was distinguished from its nearest extinct relatives by 37 osteological synapomorphies, including 24 characters of the cranium and dentition. Within Mammalia, Multituberculata was identified as the sister taxon of Marsupialia plus Placentalia. The 91 craniodental characters employed by Rowe (1988) are reevaluated here and placed in one of five categories: characters needing no alteration (11); characters with a derived state occurring in an outgroup not considered by Rowe (8); characters for which the distribution given by Rowe is altered (16); characters for which the description given by Rowe is modified (30); and characters that are excluded from further analysis (26). The distributions of the characters in the first four categories are scored among the seven taxa considered by Rowe (1988) plus Cynognathus, Diademodon, Probainognathus, Tritheledontidae, Sinoconodon, Dinnetherium, Kuehneotherium, Haramiyidae, and Vincelestes. The ensuing taxon/character matrix for all (or subsets of) these 16 taxa are analyzed with several PAUP runs. The major difference between the most parsimonious trees produced here and by Rowe is the reversed position of Monotremata and Multituberculata—i.e., in this report Multituberculata is the first outgroup to Mammalia sensu Rowe. Moreover, the boundary between Mammalia and it nearest extinct relatives is not very distinct, because only five unequivocal craniodental synapomorphies of Mammalia are identified.