Mesotheriidae - Classification

Classification

Within the order Notoungulata, Mesotheriidae is placed in the suborder Typotheria (Cifelli, 1993). In fact, Typotheria is named for the genus Typotherium, a synonym of Mesotherium (Shockey et al., 2007). In addition to Mesotheriidae, Typotheria traditionally includes other small bodied notoungulates in the families Oldfieldthomasiidae, Interatheriidae, and Archaeopithecidae (Simpson, 1967; McKenna and Bell, 1997). Recent opinion, however, favors inclusion of two additional families in Typotheria, Archaeohyracidae and Hegetotheriidae (Croft and Anaya, 2006). These families have traditionally been placed in a separate suborder, Hegetotheria, but phylogenetic studies indicate that their exclusion would render Typotheria paraphyletic (Cifelli, 1993; Billet et al., 2007). Within Typotheria, both Cifelli and Billet et al. indicate that mesotheriids are more closely related to archaeohyracids and hegetotheriids than to the remaining typotherian families. In fact, Billet et al.'s analysis indicates that both Mesotheriidae and Hegetotheriidae originated from within Archaeohyracidae.

McKenna and Bell (1997) recognized three subfamilies within Mesotheriidae: Fiandraiinae, Mesotheriinae, and Trachytheriinae. However, Flynn et al. (2005) have suggested that Fiandraia, the only known fiandraiine, is not a mesotheriid and may represent a toxodontid instead. Of the remaining subfamilies, Trachytheriinae includes earlier (Eocene and Oligocene) forms and may be paraphyletic with respect to Mesotheriinae, which includes more derived genera from the Miocene and later (Reguero and Castro, 2004).

Classification of Mesotheriidae:

  • Family †Mesotheriidae
    • Subfamily †Fiandraiinae
      • †Fiandraia (Miocene)
        • †F. romeroi
    • Subfamily †Trachytheriinae (paraphyletic)
      • †Trachytherus (?l. Eocene-l. Oligocene)
        • †T. alloxus
        • †"T. mendocensis"
        • †T. spegazzinianus
        • †T. subandinus
    • Subfamily †Mesotheriinae
      • †Eotypotherium (e. Miocene)
        • †E. chico
      • †Altitypotherium (e. Miocene)
        • †A. chucalensis
        • †A. paucidens
      • †Microtypotherium (m./l. Miocene)
        • †M. choquecotense
    • Subfamily †Mesotheriinae (continued)
      • †Eutypotherium (m. Miocene)
        • †E. lehmannnitschei
        • †E. superans
      • †Caraguatypotherium (m.-l. Miocene)
        • †C. munozi
      • †Plesiotypotherium (l. Miocene)
        • †P. achirense
      • †Typotheriopsis (l. Miocene)
        • †T. chasicoensis
        • †T. silveyrai
      • †Pseudotypotherium (l. Miocene-?m. Pleistocene)
        • †P. exiguum
        • †P. subinsigne
      • †Mesotherium (e.-m. Pleistocene)
        • †M. cristatum
        • †M. hystatum
        • †M. maendrum
        • †M. pachygnathum
      • †Hypsitherium (e. Pliocene)
        • †H. bolivianum





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