By far the most diverse (taxonomically) and dominant (numerically) order of endemic South American ungulates are the Notoungulata, literally the "southern ungulates."  Though an estimate of their specific diversity is not possible (the number of valid species, inadvertently exaggerated by early workers, is still being sorted out), a reasonable estimate of their generic diversity includes more than 150 "genera" in 13 families.  They lived in South America throughout the Cenozoic, but only a single genus, Toxodon, ever emigrated from South America; it spread into tropical Central America during the Pleistocene after the formation of the Panamanian land bridge.  
     Notoungulates are united by characters of the ear region and the dentition, including the presence of a loph on the upper molars known as the "crochet".   A northern hemisphere group of Paleogene mammals known as arctostylopids have traditionally been included in the Notoungulata, but it now appears that the similarities in the dentition of these two groups were acquired independently.  Thus, with the exception of Toxodon, the notoungulate radiation was an exclusively South American phenomenon.
      Cifelli's (1993) analysis of notoungulate relationships suggests that notoungulates can beNotoungulate Families Cladogram divided into two main groups, Toxodontia and Typotheria, plus two basal notoungulate families (see figure to the right).  Toxodontia includes medium to large rhino or horse-like animals; the group is named for its most recent representative, Toxodon, which survived until the Pleistocene megafaunal extinction   some 10,000 years ago.  Typotheria includes small to medium mammals that are mostly rodent or rabbit-like in overall form; the group is also named for one of its most recent representatives, Typotherium , now more properly known by the name Mesotherium .  Typotheres are characterized (at least at the base of the clade) by the presence of a "face" pattern of fossettes in the upper teeth.  Some representatives in both of these groups evolved simplified, ever-growing (hypselodont) cheek teeth, the only ungulates besides Elasmotherium (Perissodactyla: Rhinocerotidae), to do so.   Phylogenetic studies suggest that hypselodonty probably evolved at least four times within the Notoungulata (within the Toxodontidae, Interatheriidae, Mesotheriidae, and Hegetotheriidae).
     Follow the links below to explore notoungulate families in more detail:
Archaeohyrax patagonicus
Oldfieldthomasia debilitata


This page was last updated on December 12, 2006.