Range: Paleocene to (at least) Miocene of South America
Phylogeny: Notoungulata ::: Typotheria + *.
Note: These are the pig, hippo, and perhaps elephant analogues of the South American Paleogene. Many were quite large.
Image: Toxodon from Dinosaurios y animales prehistoricos argentinos.
Links: Toxodontia; Paleobiology 23(1) - Bruce J. MacFadden and Bruce J. Shockey; pal4 (species list); Revista geol ica de Chile - Nuevos restos de toxodonte ( .... ATW031207.
Range: Late Paleocene to Pleistocene of South America [C85].
Phylogeny: Notoungulata ::: Toxodontia + *.
Characters: mostly small, with specialized incisors and rodent-like zygomasseteric structure [C85]; base of zygomatic arch expanded & flattened [C93]; I1 enlarged [C93]; "antecrochet" (= mesial crochet?) which contacts the "first crista in the upper molars" (= protoloph?) [C85]; "face" pattern on upper molars [C93]; trigonid & talonid divided by deep buccal sulcus [C93].
Notes: Typotherians of the family Hegetotheriidae are well-known as the South American endemic analogue of rodents. Curiously, the rodents they most resemble are the Caviidae, guinea pigs and "Patagonian hares," forms which are also native to South America. The caviids are descendants of immigrant rodents who arrived in South America in the Miocene. It thus seems likely that the "caviid" specializations of both the true caviids and the hegetotheriid typotheres were acquired at the same time, presumably in competition with each other. The similarity of these two groups extends well beyond general physical resemblance and includes very close resemblance of neocortical sulci and other external brain morphological markers. [CB98] [D96].
Image: Protypotherium minitum from The Natural Canvas.
Links: Typotheria; Nathis Fauna Zuid-Amerikaanse hoefdieren Dutch).
References: Cerdeño & Bond (1998) [CB98]; Cifelli (1985) [C85]; Cifelli (1993) [C93]; Dozo 1996). ATW021225.