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 ).

Figures

Figure 1. Phylogenies of the order Litopterna illustrating its interordinal relationships (A–B) and its interfamilial relationships (C–D). A, Buckley (2015) phylogeny.B, Westbury et al. (2017) phylogeny. C, Cifelli (1993) phylogeny. D, Bonaparte and Morales (1997) phylogeny. Different colours in the branches indicate different families or orders: blue Adianthidae; brown, Notopterna; green, Proterotheriidae; red, Macraucheniidae; yellow, Sparnotheriodontidae. Litopterna is indicated with a star, but other nodes or tips of relevance are indicated in circles: blue, orders; orange, suborders; pink, superfamilies; black, families; green, non-defined rank.Abbreviations:Ad, Adianthidae; An, Anisolambdidae; Di, Didolodontidae; I, Indaleciidae; L, Litopterna; Lo, Lopholipterna; Ma, Macraucheniidae; Mo, Macrauchenoidea; Nu, Notoungulata; Pa, Panperissodactyla; Pe, Proterotheriidae; Po, Protolipternidae; S, Sparnotheriodontidae.

Figure 2. Diversity of litoptern and associated early SANU families expressed as the number of genera.A, pie chart expressing the relative diversity of each family. B, diversity over time of the different families of interest with colours corresponding to the families listed in (A). C, same as (B) but using a smoothing function that averages the different occurrences aiding the eye in seeing patterns. In (A) the number of genera for each family is indicated next to the name between brackets.In (C) the function geom_smooth from the R package ggplot v.3.4, method = loess and span = 0.5 was used.In (B) and (C) apart from the standard Periods, Epochs, and Ages below, the SALMAs are indicated in grey boxes crossing the plots. The Tiupampan and Peligran SALMAs and the Bonaerian and Lujanian SALMAs are taken as only two temporal units instead of four for the plots. The data on taxa and occurrences were taken from Supporting information, Table S1, and the temporal information on SALMAs were taken from Supporting information, File S6. Note that the two genera of ‘amilnedwarsids’ were not included in this plot.Note that in the Discussion section, we proposed to redefine the families Anisolambdidae and Sparnotheriodontidae as the subfamilies Anisolambdinae and Sparnotheriodontinae of the family Anisolambdidae. Abbreviations: Ba, Barrancan; Bo/Lu, Bonaerian and Lujanian; Cc, Colloncuran; Cd, Carodnia Zone; Ch, Chasicoan; Co, Colhuehuapian; Cp, Chapadmalalan; De, Deseadean; En, Ensenadan; Hu, Huayquerian; It, Itaboraian; La, Laventan; Ma, Marplatan; Mo, Montehermosan; Mu, Mustersan; Ri, Riochican; Sa, Sapoan; San, Santacrucian; Tg, Tinguirirican; Ti/Pe, Tiupampan and Peligran; Va, Vacan.

Figure 4. Right upper molars of Litopterna in occlusal view.A, M3 of Polymorphis ligatus (holotype, MLP 12-2169). B, M3 of Polymorphis? (AMNH-VP 29481). C, M2? of Polyacrodon lanciformis Roth, 1899 [MLP 12-2170 (mirrored)]. D, P1–M3 of Cramauchenia normalis (MLP 85-VII-3-38a). E, P1–M3 of Theosodon garretorum (FMNH P 13175). F, P5–M3 of Proectocion precisus (holotype; MACN A 10679). G, P2– M3 of Tricoelodus bicuspidatus [cast of MLP 61-IV-11-65 (P2–P4 mirrored)]. H, M3 of Proectocion argentinus (holotype; MACN A 10673). I, M1 of Lambdaconus suinus [MNHN.F.DES162 (mirrored)]. J, P1–M3 of Diadiaphorus majusculus (MLP 12-304). K, P4–M3 of Lambdaconus suinus (MACN A 52-198; P4 was mirrored). L, M1–M3 of Victorlemoinea prototypica (AMNH-VP 111963, M1 (cast of MNRJ specimen); cast of MNRJ 1470V, M2 (holotype; mirrored); cast of MNRJ 1472V, M3 (mirrored). M, M1–M3 of Paranisolambda prodromus (cast of DGM 304M, M1; cast of DGM 310M, M2–M3). N, P4–M3 ofAnisolambda sp. (MLP 59-II-28-68, P4-P5 (mirrored); MLP 59-II-24-453, M1; MNHN.F.CAS 486, M2 (mirrored); MNHN.F.CAS488, M3 (mirrored). O, P5? of Wainka tshotshe (holotype; AMNH VP-28505 (mirrored). Relevant anatomical features of the dentition are labelled. Taxa with two prehypocristae are numbered from buccal (phyc1) to lingual (phyc2). When there are two cristae originating from the same cusp, they are numbered. More information on the specimens and observations are in Supporting information, File S2. For information about the tooth position convention, check the Material and methods. Abbreviations: hy, hypocone; hys, hypostyle; me, metacone; ms, mesostyle; mtl, metaconule; pa, paracone; phyc, prehypocrista; pmc, premetacrista; pmlc, premetaconular crista; pplc, preparaconular crista; pr, protocone; prl, paraconule; prt, protostyle; psmlc, postmetaconular crista; psplc, postparaconular crista; psprc, postprotocrista. Scale bars equal 1 cm.

Figure 5. Right lower molars of Litopterna in occlusal view.A, p1–p4 of Polymorphis lechei [holotype; MLP 12-2168 (mirrored)]. B, p1–m3 of Cramauchenia normalis [MNHN.F.COL181 (mirrored)]. C, m3 of Cramauchenia normalis (AMNH-VP 29753). D, p1–m3 of Theosodon lydekkeri [MACN A 24-90 (mirrored)]. E, m2–m3 of Proectocion sp. (MLP 59-II-28-107). F, p5–m3 of Tricoelodus bicuspidatus (MACN A 52-203, p5–m2 (holotype); cast of FMNH P14696, m3). G, p2–m3 of Proadiantus excavatus (MACN A 52-214). H, p1, dp2–dp5 and m1–m3 of Lambdaconus suinus (MACN A-52-199, p1, dp2–dp5 and m1–m2; MNHN.F.DES159, m3). I, p1–m3 of Diadiaphorus majusculus (MACN A 9180-82, p2–m3; YPM PU 15799, p1). J, m1–m3 of Anisolambda fissidens (MACN A 10668; holotype).K, m2–m3 of Paranisolambda prodromus (cast of MNRJ 1496V, m2 (mirrored); cast of MNRJ 1859V, m3 (mirrored). L, m2 of Victorlemoinea prototypica (MNRJ 1482V). M, p1–m3 of Sparnotheriodon epsilonoides (MACN 18225; holotype). N, O, m3 of Wainka tshotshe? [AMNH VP-29101 (mirrored)]. Relevant anatomical features of the dentition are labelled.More information on the specimens and observations are in Supporting information, File S2. For information about the tooth position convention, check the Material and methods. Abbreviations:end, entoconid; hlph, hypolophid; hyd, hypoconid; hyld, hypoconulid; med, metaconid; mlph, mesolophid; pad, paraconid; prd, protoconid; prgd, precingulid; psmcd, postmetacristid.Scale bars equal 1 cm.