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 272446 10.1093/zoolinnean/zlad043 81098796-8acf-4360-a625-ad76a281e99e 0024-4082 8426263 Protypotherium compressidens Ameghino, 1891b ( Figs 5 , 6 , 8E–K ; Supporting Information, Table S2) 1891b Protypotherium compressidens Ameghino , p. 292 (original description). Holotype : MACN-A 4029 ( Fig. 8E ), less maxillary fragment with P3–M3, and MACN-A 4030 ( Fig. 8F ), less mandibular fragment with p4 (talonid)–m3, of the same individual (see Fernández et al. 2018 ), Early–Middle Miocene , SCF, Santa Cruz Province ( Argentina ). Referred materials: MACN-A 41-55 lot b.f, less mandibular fragment with poorly preserved p3–4 (trigonid); MACN-A 3867 ( Fig. 8G ), right mandibular fragment with dp1–2–p3–4 (trigonid); MACN-A 9716–9732?g ( Fig. 8H ), right mandibular fragment with m1 (talonid)–3; MPM-PV 19761 ( Fig. 8I ), right maxillary fragment with M1–2; MPM-PV 19781 ( Fig. 8J ), right mandibular fragment with p2–m1; and MPM-PV 19782 ( Fig. 8K ), less maxillary fragment with P2–M3. Extended diagnosis: Protypotherium compressidens differs from Pr. antiquum , Pr. australe , Pr. praerutilum , Pr. columnifer , Pr. claudum , Pr. minutum , and Pr. colloncurensis by narrower cheek teeth, even more noticeable in P2–M3; from Pr. antiquum by the talonid of m3 without a labial groove; from Pr. colloncurensis and Pr. columnifer by the talonid of p2–4 sub-triangular in outline; from Pr. claudum by having p2–3 with a distinctive entoflexid; from Pr. colloncurensis by a descending process of the maxilla with a moderate development; from Pr. praerutilum by having a larger size; from Pr. minutum and Pr. distinctum by less cement covering the cheek teeth, the P2–4 with an entoflexus located in a more distal position that is slightly less expanded, M1–3 with straighter ectolophs, and infraorbital foramen above premolars; from Pr. columnifer by the talonid of p4 narrower than the trigonid; and from Pr. antiquum by the talonid of m3 without its labial groove. Geographic and stratigraphic provenance: Santa Cruz Province ( Argentina ), SCF, Early–Middle Miocene , Santacrucian SALMA. Measurements: Supporting Information, Table S2. Remarks: The ratio between the width and length of each upper molar (R W/L ) of Pr. compressidens ( holotype plus referred materials) for M1 and M2 is <0.5, whereas it is ≥ 0.55 in Pr. australe and Pr. praerutilum , and for M3 (with enlarged distal lobe), R W/L ≤ 0.42, whereas it is ≥ 0.47 in Pr. australe and Pr. praerutilum . The scaưer diagrams for M1 ( Fig. 5A ) and M2 ( Fig. 6A ) show the separation of these species in terms of the length and width of M1–2. A similar condition is observed in m1 and m2: R L/W ≤ 0.41 in Pr. compressidens , whereas it is ≥ 0.47 in Pr. australe and Pr. praerutilum , and in m3 (with enlarged talonid), R W/L ≤ 0.33 for Pr. compressidens , whereas it is ≥ 0.35 for Pr. australe and Pr. praerutilum .