Protypotherium colloncurensis, Vera & Reguero & González-Ruiz, 2017

Vera, Bárbara, Reguero, Marcelo & González-Ruiz, Laureano, 2017, The Interatheriinae notoungulates from the middle Miocene Collón Curá Formation in Argentina, Acta Palaeontologica Polonica 62 (4), pp. 845-863 : 855-858

publication ID	https://doi.org/ 10.4202/app.00373.2017
persistent identifier	https://treatment.plazi.org/id/039687EF-5E3A-FF92-48F1-B5AEFA51FAA6
treatment provided by	Felipe
scientific name	Protypotherium colloncurensis
status	sp. nov.

Treatment

Protypotherium colloncurensis sp. nov.

Figs. 5 View Fig , 7 View Fig .

Etymology: In reference to the name of the geological unit, the Collón Curá Formation, where the new taxon comes from.

Holotype: MLP 91 View Materials -IX-4-26, skull fragmented in several pieces: hemipalates with right and left M1–3, part of basicranium and posterodorsal fragment of vault ( Fig. 7A View Fig ).

Type locality: Chico River, Río Negro Province, Argentina ( Fig. 1 View Fig ).

Type horizon: Collón Curá Formation, middle Miocene (Langhian, 14.86 ± 0.13 Ma; Bilmes et al. 2013).

Material.—Estancia El Criado: MLP 91-V-1-111, right mandible with m1–3; MLP 91-V-1-129, mandible with left and right p1–m3; MLP 92-V-10-105, right mandible with p3–m3; MLP 92-X-10-119: 3, right maxilla with P3–M2; 4, right mandible with m1–3; 5, right maxilla with M1–3; 13, right maxilla with P3–M2 and broken I3–P1; 15, right mandible with p3–4; 16, left mandible with p3–m2; 18, palate with left P1–M3 and right P2–M3, and left mandible with i1–m3; 31, right mandible with p2–m1; 35, left mandible with p4–m2; 36, left mandible with p2–m2; 46, left mandible with p4– m1; 50, right maxilla with M1–2. Cerro San Antonio: MLP 74-II-1-1 (originally assigned to Epipatriarchus sp. ), left maxilla with P1–M2. Comallo: MLP 92-XI-18-31: a, right maxilla with M1–3; b, right maxilla with M3; c, right and left i1–3; d, left lower molar; e, M3 (a, c–e, probably same individual). Collón Curá Formation (Río Negro Province, Argentina), middle Miocene. Figure 1 View Fig details the localities referenced here.

Diagnosis.— Protypotherium colloncurensis is larger (38% in linear measurements) than Protypotherium endiadys and differs from it because of its higher and more robust mandible; wider upper canine; well-developed parastyle in P1; P2 overlaps P1; strongly imbricated upper molars, which have a well-developed and forwardly extended parastyle, a more strongly folded ectoloph, curved lingual sulcus, and without fossettes; molar size decreases markedly from M1 to M3; very procumbent lower incisors; p1 is subcircular and different from premolars, non-overlapping; very reduced p2; much smaller talonid in relation to trigonid in p3–4; and trigonid of molars narrows and shortens from m1 to m3.

Description.—Skull and upper dentition: The MLP 91-IX- 4- 26 holotype preserves the zygomatic arches, which are dorsoventrally low, and the anterior part of the zygomatic arch is laterally wide ( Fig. 7A View Fig ). In ventral view, the maxillary process of the zygomatic arch is a moderately concave triangular surface widening posteriorly. The descending process of the maxilla is barely developed ( Fig. 7A View Fig 2 View Fig ), as in P. endiadys .

Upper incisors are not known for P. colloncurensis . In comparison with P. endiadys , P. colloncurensis has a wider C ( Table 3), and P1 has a well-developed parastyle and is overlapped by P2 ( Fig. 7B View Fig ). P2–4 have a strongly folded ectoloph, with a peculiar wider and labially more extended parastyle than the paracone fold ( Fig. 7B View Fig ).

Molars are larger than in P. endiadys , strongly imbricated and have a labially undulated ectoloph, with a well-developed and forwardly extended parastyle, and a deep labial sulcus ( Figs. 5 View Fig , 7A, C View Fig ); no fossettes are observed. M1–2 have a posterior lobe wider than the anterior lobe which has a nearly straight distal face forming an angle of 90º with the ectoloph; in contrast, in M3 the posterior lobe is triangular-shaped with the distal face drawing an angle <90°. M1 is the largest of the molar series, especially in the transverse diameter of the anterior lobe, which gives a peculiar trapezoid shape to the molar ( Fig. 7C View Fig ). Molar size decreases markedly from M1 to M3 ( Table 3) and the lingual sulcus, which divides the anterior and posterior lobes, is curve-shaped and mesially pointed. These features are also observed in Protypotherium minutum (MLP 12-2177; Table 3); in turn, P. endiadys has nearly equally-sized upper molars with transversely straight lingual sulcus ( Fig. 2A View Fig 3 View Fig , C). The most overlapped molars are present in P. distictum (MLP 12-2178; Table 3), but the latter differs from P. colloncurensis in having a bifid lingual sulcus.

Mandible and lower teeth: Incisors are very procumbent. The i1–2 are sub-circular in cross-section, i1 being the smallest of incisors and laterally flattened ( Fig. 7E View Fig ; Table 4). The i3 and c are ellipsoidal in cross-section, labiolingually flattened ( Fig. 7E View Fig ); in contrast, p1 is shorter and wider than the canine, subcircular in cross-section and non-overlapping ( Fig. 7D View Fig 1 View Fig , D 2 View Fig ), differing from the laterally compressed p 1 in P. endiadys . There are short spaces separating c from i3 and p1 ( Fig. 7D View Fig 4 View Fig ), a feature also observed in P. endiadys and Miocochilius anomopodus . Protypotherium colloncurensis has a higher and more robust horizontal ramus compared to P. endiadys ( Figs. 5 View Fig , 7D View Fig 3 View Fig ).

The p2 differs from p 1 in being larger and labiolingually flattened but, unlike p3–4, it does not have a differentiated talonid. In comparison, p3–4 are significantly larger than p2, both with well-defined trigonid and talonid ( Fig. 7D View Fig 1 View Fig , D 2 View Fig ; Table 4); p3 differs from p 4 in having a longer trigonid. Compared to P. endiadys , premolars in the new species are clearly different in size and morphology from p2 to p4; in p3–4 the talonid is much smaller than the trigonid; and p2 is a very reduced tooth. In turn, in P. endiadys premolars are similar to one another, the talonid is larger (in relation to the trigonid) than in the other species, and p2 is not so reduced, being a small version of p3–4.

The m1 and m2 are very similar to each other; they have a triangular talonid, which is slightly concave on the lingual face, becoming heart-shaped ( Fig. 7D View Fig 1 View Fig , D 2 View Fig ). The m1 has a longer mesial face than m2. The m3 differs from m 1–2 in having a longer talonid, which is labially bilobed due to a vertical sulcus ( Fig. 7D View Fig 1 View Fig , D 2 View Fig ). All molars have a square trigonid, which becomes narrower and shorter from m1 to m3; this is a difference with respect to P. endiadys , in which the trigonid of successive molars remains nearly equally-sized. Premolars and molars are covered by a thick layer of cementum, mainly on labial side ( Fig. 7D View Fig 1 View Fig , D 2 View Fig ). No deciduous dentition was identified for P. colloncurensis .

Multivariate statistics: The results of a discriminant analysis based on six variables of dentition showed a statistically significant separation among Miocene interatheres ( Fig. 8 View Fig ). The analysis yielded two discriminant functions that accounted for 95.42% of variance in the data set. Excepting width of m3, which negatively influenced scores, all variables influenced scores positively. The first discriminant function (85.78%) mainly separated the morphospace of Protypotherium endiadys , which occupies intermediate values, from Protypotherium colloncurensis , which is placed to the right of the axis. Interatherium had the lowest (negatives) values for the first discriminant function, while Miocochilius and Protypotherium colloncurensis partially overlap at the right extreme (highest positive values); these latter taxa, however, had different values for the second discriminant function. Interestingly, Protypotherium australe had a wide range of values for the first discriminant function, partially overlapping P. endiadys in the negative values and P. colloncurensis in the positive values. This indicates variability between the Santacrucian specimens of Protypotherium .