Systematic review of fossil Trernarctinae (Carnivora, Unidae) from South America. The systematics, and the gcog~aphic and stratigraphic distribution of the South hnnerican fossil taxa of Tremarctinae (Carnivora, Ursidae) arc reviewed and discussed. Now diagnostic charactors are proposed, in order to support each taxan. Only one genus (Arctotheriurn), of the Pleistocene and Lower Halocone of South America, is recognized, with five species: A, rvetusturn Anleghino, A, wingei Ameghino, A.

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... ns Gervnis & Ameghino, A. bonariense (Gervuis), and A. tarijensi. Ameghino. ArcloNzeriurn is record& from the Ensenadan (Upper Pliocene to Middle Pleistocene) to the 1,ujanian (Upper Pleistocene to Lower Holocene) in Venezuela, Brazil, Bolivia, Uruguay, Argentina, and Chile. A. uetusticnt is recorded in the Bonaorian (Middlo Pleistocene) in Argentina; A. wingei in the Lujanian in Venezuela, Bolivia and Brazil; A. angustidens in the Ensenadan of Bolivia and Argentina; A. bonarierzsi. in thc Roriaerian and Lujmian of Argentina and A, larljense in the Bonaerinn and Lujanian of Uruguay, Argentina, and Chile. Aretotheriurn is characterized hy ten features: the post palatino margin slightly overpasses the dislal end of M2, Pi-3 compressed in a triangular arrangement, prolocone reduced or absent in P4, len@h between canine and P4 less than 1' 4 mesio-ciilistai length, metastylereduccd or absent in MI, MZ wider than in othor ursids, p4 crown ellipsoidal shaped, m l trigonid wider than in other ursids, m2 crown kidney shaped, m3 crown sub cii'ciilate shapod.