Mammal Classification - Luo, Kielan-Jaworowska, and Cifelli Classification

Luo, Kielan-Jaworowska, and Cifelli Classification

Several important fossil mammal discoveries have been made that have led researchers to question many of the relationships proposed by McKenna and Bell (1997). Additionally, researchers are subjecting taxonomic hypotheses to more rigorous cladistic analyses of early mammal fossils. Luo et al. (2002) summarized existing ideas and proposed new ideas of relationships among mammals at the most basal level. They argued that the term mammal should be defined based on characters (especially the dentary-squamosal jaw articulation) instead of a crown-based definition (the group that contains most recent common ancestor of monotremes and therians and all of its descendants). Their definition of Mammalia is roughly equal to the Mammaliaformes as defined by McKenna and Bell (1997) and other authors. They also define their taxonomic levels as clades and do not apply Linnean hierarchies.

Mammalia

• †Sinoconodon - earliest and most basal of mammals
• Unnamed clade 1 - a clade that contains all other mammals. These are characterized by determinant growth and occlusal features of the cheek teeth.
  • †Morganucodontidae - morganucodontids, including †Morganucodon, †Megazostrodon, and others
  • †Docodonta - docodonts, including †Haldanodon and †Castorocauda (Ji et al., 2006)
  • Unnamed clade 2 - a clade containing all living mammals and some fossil relatives. It is characterized by the loss of a postdentary trough and a widened braincase.
    • †Hadrocodium
    • †Kuehneotherium
    • Crown-group Mammalia - the group that contains most recent common ancestor of monotremes and therians and all of its descendants. This group is defined by additional characters relating the occlusion of molars and the presence of a well-developed masseteric fossa.
      • Australosphenida - a clade that contains monotremes and their fossil relatives. These fossils include †Ambondro, †Asfaltomylos, †Ausktribosphenos, and †Bishops. If correct, this clade represents an independent evolution of the tribosphenic molar in southern continents.
      • Trechnotheria - Therians, spalacotheriids and their relatives. They are characterized by features of the scapula, tibia, and humerus.
        • †Spalacotheriidae - including Akidolestes, Zhangheotherium, and Maotherium.
        • Cladotheria - Therians, dryolestids, and their relatives. They are characterized by features of the tribosphenic molar and the angular process of the dentary.
          • †Dryolestidae
          • †Amphitherium - incertae sedis (it may be a prototribosphenidan)
          • Prototribosphenida - Therians and fossil relatives including †Vincelestes. Characterized by features of the cochlea including coiling.
            • †Vincelestes
            • Zatheria - Therians and fossil relatives including the "peramurids". Characterized by the presence of wear in the talonid of the lower molars.
              • †"Peramuridae" - †Peramus and relatives. Known only from preserved mandibles and distinctly zatherian molars.
              • Boreosphenida - Therians and fossil relatives including †Kielantherium. They are characterized by molar features.
                • †Kielantherium
                • †Deltatheroida including †Deltatheridium - incertae sedis (it may represent a metatherian)
                • Crown-group Theria - the group that contains most recent common ancestor of marsupials and placentals and all of its descendants. Characterized by a host of molar features, aspects of the alispenoid, and aspects of the astragalus region.
      • †Eutriconodonta - incertae sedis. Triconodonts appear to be a member of the crown-Mammalia clade, but their relationships within it are unknown. It is also not certain that they represent a monophyletic group. Examples include Repenomamus.
    • †Multituberculata - incertae sedis. Luo e al. (2002) argue that multituberculates cannot be confidently placed in a particular clade of mammals. They suggest that they represent either basal mammals or are sister to the Trechnotheria.