Proterotheriidae (Odreman Rivas, 1969)

Püschel, Hans P., Shelley, Sarah L., Williamson, Thomas E., Perini, Fernando A., Wible, John R. & Brusatte, Stephen L., 2024, A new dentition-based phylogeny of Litopterna (Mammalia: Placentalia) and ‘ archaic’ South American ungulates, Zoological Journal of the Linnean Society 202 (1), pp. 1-50 : 9-11

Proterotheriidae ( Figs 4J–K, 5H–I)

With 28 currently accepted genera, Proterotheriidae is the most diverse family of litopterns ( Fig. 2A; Supporting information, Table S1 ), being particularly diverse during the Neogene alongside macraucheniids ( Fig. 2B–C). Soria (2001) presented a major revision of this family, so to avoid unnecessary repetition, only the most important taxonomical aspects and the main advances since his revision are discussed here. Proterotheriidae was named by Ameghino (1887) with the description of the genera Proterotherium Ameghino, 1883 , Thoatherium Ameghino, 1887 , Diadiaphorus Ameghino, 1887 , and Licaphrium Ameghino, 1887 . Simpson (1945) subdivided this family into two subfamilies, Polymorphinae and Proterotheriinae , the former including taxa mostly from the Palaeocene and Eocene (Peligran to Mustersan SALMAs) and the later the taxa from the Late Oligocene onwards (Deseadean SALMA). Although this classification was followed by other authors ( Lavocat 1958, Paula Couto 1979), Simpson (1948) did not employ this subfamilial division and only used the family Proterotheriidae , without giving any explanation for this omission. Later, Odreman-Rivas (1969) modified the subfamily Polymorphinae from Simpson’s (1945) proposal, keeping Polymorphis Roth, 1899 (including Polyacrodon ligatus Roth, 1899 and Heteroglyphis Roth, 1899 ), and excluding the rest of the taxa such as the now considered anisolambdids Wainka Simpson, 1935 and Anisolambda Ameghino, 1901 (including Ricardolydekkeria Ameghino, 1901 and Josepholeidya Ameghino, 1901 ) and the didolodontid Xesmodon Berg, 1899 .

Cifelli(1983a)subdividedthefamilyProterotheriidaeintotwo subfamilies, Anisolambdinae and Proterotheriinae , the former subfamily including mostly anisolambdids (see Anisolambdidae section for more details), and the latter similar to the original definition of Simpson (1945). In addition, Cifelli (1983a) excluded the subfamily Polymorphinae from Proterotheriidae , placing it insteadwithinthefamilyMacraucheniidae (seeMacraucheniidae section for more details). Soria (2001) later removed the subfamily Anisolambdinae from Proterotheriidae , elevating its rank as a distinct family (see Anisolambdidae section for more details), which leaves the concept of Proterotheriidae very similar to the subfamily Proterotheriinae from Simpson (1945), although with numerous new additions to the family since then (e.g., Corona et al. 2020, McGrath et al. 2020a; Supporting information, Table S1 ). Important additions to Proterotheriidae were the bunodont Megadolodus molariformis McKenna, 1956 and Neodolodus colombianus Hoffstetter & Soria, 1986 ( Cifelli and Diaz 1989, Cifelli and Villarroel 1997, McGrath et al. 2020b), which were previously considered didolodontids ( McKenna 1956, Hoffstetter and Soria 1986). Including both taxa within Litopterna has phylogenetic support, but their affinities within Proterotheriidae and even other litoptern families are unclear (Carrillo et al. 2023).

Proterotheriidae has been included by some authors as part of suborder Lopholipterna (Cifelli 1983a, Soria 2001; Table 1 ), which also includes the families Adianthidae and Macraucheniidae , a hypothesis that later found phylogenetic support ( Cifelli 1993; Fig. 1C). Since then, most phylogenetic studies that included proterotheriids have focused either on resolving the affinities within Proterotheriidae (e.g., McGrath et al. 2020b) or phylogenies studying interordinal relationships between SANUs (e.g., MacPhee et al. 2021) instead of phylogenies examining the interfamilial affinities of proterotheriids ( Table 2 ).

Following Soria’s (2001) concept of the family, the earliest proterotheriid is Lambdaconus suinus Ameghino, 1897 from different localities from the Sarmiento Formation, Chubut, Argentina, and the last is Neolicaphrium recents Frenguelli, 1921 from the Late Pleistocene from different localities in Argentina, Brazil, and Uruguay ( Gaudioso et al. 2017), giving a temporal interval of around 29.3–~0.11 Mya to this family ( Fig. 2B; Supporting information, Table S1 ).