Systematic revision of the species of Protypotherium (Notoungulata: Interatheriidae) from the Santa Cruz Formation (Early-Middle Miocene), Argentinian Patagonia: a new phylogenetic hypothesis for the Interatheriidae Author Fernández, Mercedes División Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales ‘ Bernardino Rivadavia’, Avenida Ángel Gallardo 470, C 1405 DJR Ciudad Autónoma de Buenos Aires, Argentina & Laboratorio Anatomía y Evolución de los Vertebrados, Departamento de Ciencias Básicas, Universidad Nacional de Luján, Ruta 5 y Avenida Constitución 6700 Luján, Buenos Aires, Argentina & Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Juan Domingo Perón 2158, C 1040 AAH, Buenos Aires, Argentina mechisfernandezpaleo@gmail.com Author Fernicola, Juan C. División Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales ‘ Bernardino Rivadavia’, Avenida Ángel Gallardo 470, C 1405 DJR Ciudad Autónoma de Buenos Aires, Argentina & Laboratorio Anatomía y Evolución de los Vertebrados, Departamento de Ciencias Básicas, Universidad Nacional de Luján, Ruta 5 y Avenida Constitución 6700 Luján, Buenos Aires, Argentina & Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Juan Domingo Perón 2158, C 1040 AAH, Buenos Aires, Argentina Author Cerdeño, Esperanza Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Juan Domingo Perón 2158, C 1040 AAH, Buenos Aires, Argentina & Paleobiología y Paleoecología, Instituto de Nivología, Glaciología y Ciencias Ambientales, Centro Científico Tecnológico-CONICET-Mendoza, Avenida Ruiz Leal s / n, M 5500 Mendoza, Argentina text Zoological Journal of the Linnean Society 2023 2023-07-11 199 2 417 444 http://dx.doi.org/10.1093/zoolinnean/zlad043 journal article 10.1093/zoolinnean/zlad043 0024-4082 8426263 Protypotherium antiquum Ameghino, 1885 ( Fig. 4A–B ; Supporting Information, Table S2) 1885 Protypotherium antiquum Ameghino , p. 81–83 (original description). Lectotype : ZMK 21 /1877 ( Fig. 4A ), right mandibular fragment with p4–m3 (see Fernández et al. 2018 ), from Late Miocene, Ituzaingó Fm. , Entre Ríos Province ( Argentina ). Referred material: IBIGEO-P39 ( Fig. 4B ), less mandibular fragment with p4–m3; MCH-P 257, right mandibular fragment with p3–m1 ( Armella and Bonini 2020 ). Extended diagnosis: Protypotherium antiquum differs from Pr. australe , Pr. praerutilum , Pr. columnifer , Pr. compressidens , Pr. minutum , Pr. claudum , and Pr. colloncurensis by having the talonid of m3 with a very deep longitudinal and transverse labial sulcus and a mesio-labial lobe distally straight; from Pr. compressidens by having relatively wider lower cheek teeth; from Pr. claudum by exhibiting a p4 with a transversely deeper, narrower, and more distally placed ectoflexid, and m1–3 with deeper entoflexid; from Pr. colloncurensis and Pr. columnifer by the sub-triangular talonid of p4; from Pr. praerutilum by having a slightly larger size; and from Pr. columnifer by the talonid of p4 narrower than the trigonid. Geographic and temporal provenance: Entre Ríos Province ( Argentina ), Ituzaingó Fm .; Salta Province , Palo Pintado Fm. ( Zimicz et al. 2018 ); and Catamarca Province , Chiquimil Fm. ( Armella and Bonini 2020 ); Late Miocene , Huayquerian SALMA . Measurements: Supporting Information, Table S2. Remarks: Zimicz et al. (2018) identified IBIGEO-P39 ( Fig. 4B ) as Pr.minutum mainly due to size and a trilobed m3. Nevertheless, these authors mentioned that it resembled the remaining species of the genus. Concerning these features, the presence of a trilobed m3 is common in Protypotherium and it is not exclusive of Pr. minutum ( holotype MLP 12-2176) (see above). When comparing the m3 of MLP 12-2176 and IBIGEO-P39, the labial groove of the former is transversally shallow, but persistent, and in both the distal face of the mesio-labial lobe and the disto-labial lobe of the talonid are rounded. Instead, this groove is transversally deeper and persistent in IBIGEO-P39 ( Fig. 4B ) and the distal face of the mesio-labial lobe is straight, which is coincident with the diagnostic features of Pr. antiquum . In addition, IBIGEO-P39 (e.g. Lm1 = 6.26 mm ; Wm1 ≈ 3.2 mm ) is intermediate in size between Pr. minutum (e.g. Lm1 ≈ 4.6 mm ; Wm1 ≈ 2.60 mm ) and Pr. antiquum (e.g. Lm1 = 7.4 mm ; Wm1 ≈ 4.1 mm (see Supporting Information, Table S2), being even closer to the laưer. Therefore, mainly based on the morphological features, we re-identify IBIGEO-P39 as Pr. antiquum . On the other hand, we state that MCH-P 257, mentioned as Protypotherium cf. Pr. antiquum by Armella and Bonini (2020) , also corresponds to Pr. antiquum , sharing the same mentioned features with IBIGEO-P39.