Skull and reproduction of head of Notopithecus, from here.

Belongs within: Panameriungulata?.

The Notoungulata were a diverse group of herbivorous mammals found in South America from the Palaeocene to the Pleistocene. Various forms might be described as convergent on Northern Hemisphere rhinos, pigs, rabbits or hyraxes. The relations of notoungulates within other mammals remain poorly established; also subject to much debate is whether the Arctostylopida from the Palaeocene and Eocene of Asia and North America are members of this otherwise entirely South American group.

Characters (from Rose 2006): Early forms with dental formula of; teeth usually closely spaced, diastema absent; cheek teeth lophodont: upper molars with strong, straight ectoloph, oblique protoloph and more transverse metaloph; tendency to develop extra crests running toward centre of upper molar, including 'crochet' extending anterobuccally from metaloph; lower molars with two main crescentic crests, the metalophid and hypolophid, with shorter transverse entolophid derived from entoconid; paraconid typically absent; paracristid short; ectocingulum usually weak or absent on both upper and lower teeth. Skull with postorbital bar absent, zygomatic arch arising high on back of skull. Ear region with tympanic cavity connected to large epitympanic sinus in squamosal, often also to hypotympanic sinus below tympanic cavity; inflated ectotympanic bulla surrounding tympanic cavity, extending laterally as external auditory tube with ventral crest; fossa present behind bulla for projection of the hyoid. Feet mesaxonic; astragalus with moderately long constricted neck, roughly hemispherical head, medial projection on body, prominent dorsal foramen, posterior sulcus, partly confluent sustentacular and navicular facets; astragalar trochlea slightly grooved with high lateral rim; calcaneal peroneal tubercle distally situated.

    |  i. s.: Simpsonotus MC00
    |         Notostylops MC00
    |           |--N. brachycephalus S32
    |           `--N. escaridus S32
    |--Oldfieldthomasia [Acoelodidae] S32
    |    `--O. debilitata [=Acoelodus debilitatus] S32
    |--Notopithecus [Notopithecidae] S32
    |    `--N. adapinus S32
    `--Actostylopidae [Actostylopida] HC97
         |--Asiostylopinae HC97
         |    |--Asiostylops HC97
         |    `--Bothriostylops Zheng & Huang 1986 HC97
         |         |--B. notios HC97
         |         `--B. progressus (Tang & Yan 1976) HC97
         `--Actostylopinae HC97
              |--Allostylops periconotus HC97
              |--Actostylops HC97
              `--Paleostylops HC97
                   |--P. iturus HC97
                   `--P. macrodon HC97


[HC97] Huang X. & Chen L. 1997. Mammalian remains from the Late Paleocene of Guichi, Anhui. Vertebrata PalAsiatica 35 (1): 49-67.

[MC00] Muizon, C. de, & R. L. Cifelli. 2000. The “condylarths” (archaic Ungulata, Mammalia) from the early Palaeocene of Tiupampa (Bolivia): Implications on the origin of the South American ungulates. Geodiversitas 22 (1): 47-150.

Rose, K. D. 2006. The Beginning of the Age of Mammals. JHU Press.

[S32] Simpson, G. G. 1932. Skulls and brains of some mammals from the Notostylops beds of Patagonia. American Museum Novitates 578: 1-11.

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