Abstract

The phylogenetic interrelationships of Eucynodontia are very important topic in vertebrate paleontology and are the foundation to understand the origin of mammalian. However, the consensus on the phylogenetic interrelationships of Eucynodontia remains elusive. To clarify these phylogenetic interrelationships of Eucynodontia, a cladistics analysis, based on 145 characters and 31 species and integrated all prior works, was performed. The monophyly of Eucynodontia is confirmed, although the results differ slightly from those of previous analyses with respect to the composition of both Cynognathia and Probainognathia. This is also the first numerical cladistic analysis to recover a monophyletic Traversodontidae. Tritheledonta cannot be monophyletic in any case, and this name is not recommended for formal taxonomic use. Brasilodon is the plesiomorphic sister taxon of mMammalias, although it is younger than the oldest mammals and is specialized in some characters. A monophyletic Mammaliamorpha, including all trithelodontans, tritylodontids and mammals, is well supported by many characters.
Pruning highly incomplete taxa has little effect on the inferred pattern of relationships among the more complete taxa, although this pattern can change according to the inclusion or exclusion of basal fragmentary taxa. Different taxa Taxon sampling onf the current data matrix shows that taxon sampling was poor in some previous studies, implying that their results are not reliable. Two major unresolved questions in cynodont phylogenetics are whether tritylodontids are more closely related to mammals or to traversodontids, and whether tritylodontids or trithelodontids are closer to mammals. We compare previously topologies and our topology for congruence with the stratigraphic record. Analysis Analyses of possible synapomorphies and stratigraphic data supports a relatively close relationship between mammals and tritylodontids, to the exclusion of traversodontids, but does not clearly indicate whether or not trithelodontids are even more closer to mammals than are tritylodontids.