Protypotherium endiadys ( Roth, 1899 ) 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 : 848-855

publication ID	https://doi.org/ 10.4202/app.00373.2017
persistent identifier	https://treatment.plazi.org/id/039687EF-5E33-FF95-4804-B587FE4DF91A
treatment provided by	Felipe
scientific name	Protypotherium endiadys ( Roth, 1899 )
status	comb. nov.

Treatment

Protypotherium endiadys ( Roth, 1899) comb. nov.

Figs. 2–6 View Fig View Fig View Fig View Fig View Fig .

1899 Icochilus endiadys ; Roth 1899: 38–41, pl. 6: 1–4.

1978 Interatherium endiadys ; Pascual et al. 1978: 179.

1986 Icochilus andiadys Roth, 1899 ; Mones 1986: 153.

2011 Icochilus andiadys Roth, 1899 ; Kramarz et al. 2011: 559, fig. 2F. Holotype: MLP 12-2886,skull with left I1–M3and right P2–M3 ( Fig. 2A View Fig ).

Type locality: Collón Curá River , Neuquén Province, Argentina ( Fig. 1 View Fig ) .

Type horizon: Collón Curá Formation, middle Miocene (Langhian, ages ranging 14.0–15.5 Ma, according to Flynn and Swisher 1995).

Material.—Collón Curá River: MLP 12-2887: a, right mandible with c–p3; b, right mandible with m2–3; c, left mandible with m1–2 (a, b, same individual); MLP 12-2916: a, right mandible with m2–3; b, left mandible with m1–3; c, right i1–2 and left i2; d, right lower canine; e, right astragalus (a–e, same individual). Estancia Collón Curá: MLP 90-IX-2-170, mandible with left m3 and right i1–c and p2–3; MLP 90- XII-17-20, left maxilla with P3–M3. Sur balsa Collón Curá: MLP 90-XII-22-1, left mandible with p4–m3. Cañadón del Tordillo: MLP 91-IV-1-47, right mandible with m1–3. Pichileufú River: MLP 73-VII-7-1, right maxilla with P3– M3, mandible with right i3–p2 and left p1–2, left mandible with m1–2, and proximal of ulna; MLP 73-VII-8-4, right mandible with p3–m2. Estancia El Criado: MLP 73-V-III-63, skull with right P1–M3 and left P3–M3; MLP 73-VII-6-3, palate with right P1–M3 and left P3–M3; MLP 73-VII-6-5, right mandible with p4–m1; MLP 73-VII-6-6, right mandible with m1–2; MLP 73-VII-6-8, left maxilla with P3–M3; MLP 73-VII-6-9, mandible with left i1 and right i1–m1; MLP 73- VII-8-6, right mandible with m1–3; MLP 73-VII-9-1, skull with left I1–M1 and right I1–C, P3–M3; MLP 74-II-1-4, left mandible with p2–m3; MLP 74-II-1-16 (originally assigned to Interatherium sp. ), left mandible with m2–3; MLP 92-V-10- 106: a, left mandible with m1–3; b, right mandible with p4– m2; c, right i3–p2 and left p2; d, left maxilla with DP2–DP4 and M1; e, mandible with right dp4–m1 and left dp3–4–m1; MLP 92-V-10-108, left hemipalate with P1–M3; MLP 92-X-10-119: 1, right mandible with m1–3; 2, right maxilla with P3–M2; 6, left maxilla with P3–M3; 7, right maxilla with M2–3; 8, left maxilla with M2–3; 9, left maxilla with M2–3; 10, right mandible with p2–4; 12, left mandible with m3; 14, left mandible with p2–m3; 19, right mandible with m1–3; 23, right mandible with p3–4 and erupting m1; 24, mandible with left i1–c, p2–m1, and right i1–c, p2–3; 25, right maxilla with M1–3; 26, left mandible with p4–m3; 27, left mandible with p4–m3; 28, left maxilla with M1–3; 30, left mandible with m1–3; 32, left mandible with m2–3; 33, left mandible with p2–m1; 34, right mandible with p4–m2; 36, left mandible with p2–m2; 38, right maxilla with P1–DP2 and P3–M1; 43, right maxilla with P3–M2; 44, left mandible with p2–m1; 45, left mandible with m1–3; 46, left mandible with p4–m1; 47, left mandible with m2–3; 48, right mandible with p2–4; 49, left mandible with p4–m3. Cerro Castillo: MLP 90-XII-24-34 (originally assigned to Protypotherium sp. ): a, left mandible with m1–2; b, left mandible with m3; c, right mandible with p3–4; d, left mandible with pd2–dp4. Comallo: MAPBAR 947, left hemipalate with P1–M3; MAPBAR 953, left mandible with m1–3; MAPBAR 955, right maxilla with P3–M3; MAPBAR 958, left mandible with m1–3; MAPBAR 959, left maxilla with P1–M3; MAPBAR 960, left mandible with m1–3; MAPBAR 965, mandible with right i1, p1–m3, and left i1–c, p2–m3; MAPBAR 1381, skull with left I3–M3 and right I1–P2, P4–M3, and distal of humerus. Chico River (Río Negro Province): MLP 92-XI-16-17, right mandible with p2–m2. Chico River (Chubut Province): LIEBPV 7002, right maxilla with P3–M3. Collón Curá Formation (Neuquén, Río Negro, and Chubut provinces, Argentina), middle Miocene. Figure 1 View Fig details the localities referenced here, except for Sur balsa Collón Curá (from Roth 1899), which was not precisely located.

Emended diagnosis.— Protypotherium endiadys is characterized by: maxilla extended dorsally over the orbit; anterior process of the frontal bone is lacking; small descending process of the maxilla; slender and relatively low mandible; reduced P/p1; nearly equally-sized and barely imbricated upper molars, which have fossettes and a deep and simple lingual sulcus; well-developed posterior lobe in M3; no diastemata between the i3 and canine, or between c and p1; i1–c are moderately procumbent; p1 caniniform; p2–3 with talonid much smaller than trigonid; and lower molars with a similarly-sized trigonid. It differs from P. australe in being smaller, having a shorter rostrum and longer basicranium in relation to skull length, less imbricated upper incisors, non-overlapping P/p1, humerus with deeper trochlea and supratrochlear foramen, ulna with larger trochlear notch/ olecranon ratio, and less concave articular surface of the astragalar trochlea.

Description.—Skull and upper dentition: The MLP 12-2886 specimen is a nearly complete cranium with left I1–M3 and right P2–M3; except for the broken zygomatic arches, it is in good condition, preserving part of the palate, basicranium, nasals, frontal bones, fragmentary parietals and posterior part of skull ( Fig. 2A View Fig ; Table 1). It should be noted that the maxilla in MLP 12-2886 extends dorsally over the orbit (here named dorsal process of the maxilla) and no anterior process of the frontal bone is observed ( Fig. 2A View Fig 1 View Fig , A 2 View Fig ), such as was also noted by Roth (1899). This feature differs from other Miocene interatheres, such as Protypotherium autrale , Interatherium robustum and Miocochilius anomopodus , where the frontal bone projects anteriorly like a sliver, separating the maxilla from the orbit (Vera 2016). The rostrum of MLP 12-2886 is shorter and wider than that of Miocochilius anomopodus ( UCPM 38091), which is narrow and elongated. The bullae of MLP 12-2886 are small relative to skull size ( Fig. 2A 2 View Fig , A 4 View Fig ); the antorbital foramen is placed at M1 level; orbits are large, having a diameter of 1/3 the length of the skull. The descending process of the maxilla is little developed ( Fig. 2A 2 View Fig , A 4 View Fig ), differing from the moderate process in Protypotherium australe and the much more developed process of Interatherium . In ventral view, the palate has a transverse fracture causing a separation between I2–3 ( Fig. 2A View Fig 4 View Fig ). Permanent upper and lower cheekteeth are euhypsodont, as is typical of Miocene interatheres.

The I1 is the largest of incisors ( Fig. 2B View Fig ; Table 1); I1–I3 are elongated, labiolingualy flattened, and slightly narrowing posteriorly. The canine is labiolingually flattened, with a wide and labial convex anterior part, and a narrow, flattened and longer posterior part; it differs from the incisors because it is labially bilobed and lingually convex, instead of having the straighter faces of incisors ( Fig. 2B View Fig ).

In the holotype, an old individual, P1 is a reduced, subcircular in outline and non-overlapping tooth ( Fig. 2A View Fig 3 View Fig , A 4 View Fig ), differing from the canine and the other premolars (see below). In younger individuals (e.g., MLP 73-V-III-63 and MLP 92-V-10-108), however, P1 is not as reduced as in MLP 12-2886, and it has an incipient parastyle, like in P2. P2–4 Fig. 2A View Fig 3 View Fig , A 4 View Fig , C) are premolariform, nearly square, and completely differentiable from molars; in addition, they have a strongly folded ectoloph, and a mesial sulcus that forms two small lobes in the mesial face; this sulcus is more evident in P3–4. A tiny fossette is present in P2–4 ( Fig. 2A View Fig 3 View Fig , A 4 View Fig ).

Molars, in turn, are rectangular and equally sized Fig. 2A View Fig 3 View Fig , A 4 View Fig , C; Table 1); they have a smoothly undulate ectoloph and a deep lingual sulcus divides them into two lobes. In M1, the lingual sulcus is deeper than in M2–3. In M1–2, the posterior lobe is longer than the anterior one, whereas the condition is opposite in M3. The imbrication is remarkable between P4–M1 and M1–2. There are two fossettes, one in each lobe of the molars ( Fig. 2A View Fig 3 View Fig , A 4 View Fig ). There is a thick layer of cementum on the lingual face of P2–M3.

LIEBPV 7002 ( Fig. 2C View Fig ) is the only specimen recovered from exposures of the Collón Curá Formation at Chico River locality, Chubut Province ( Fig. 1 View Fig ). It is a fragment of maxilla with P3–M3 comparable in size and morphology to MLP 12-2886 and other specimens associated with the Protypotherium endiadys -morphotype, such as MAPBAR 959 and MAPBAR 1381 ( Table 1).

Protypotherium endiadys differs from the Laventan species of the genus Miocochilius ; M. federicoi Croft, 2007 has a better developed P1 and a lingual sulcus internally bifurcated on M1–2; in contrast, M. anomopodus Stirton, 1953 has more elongated premolars and a shallow lingual sulcus on molars. In addition, the early/middle Miocene interathere specimen referred to as Protypotherium sp. nov. from Cerdas ( Bolivia; Croft et al. 2009: fig. 8C) has longer than wide P2–3 and a tiny middle lobe in M1. Regarding younger Chasicoan interatheres, Protypotherium endiadys has a square and better developed posterior lobe in M3, whereas the MLP 12-2177 specimen ( P. minutum Cabrera and Kraglievich, 1931 ) is smaller and its M3 has a posterior lobe triangular-shaped, which is much larger than the anterior lobe; in turn, P. distinctum Cabrera and Kraglievich, 1931 (MLP 12-2178) is characterized by its larger size ( Table 1) and more imbricated upper molars, which have a peculiar bifurcated lingual sulcus.

Mandible and lower dentition: The lots MLP 12-2887 and MLP 12-2916 were both collected by Santiago Roth in Collón Curá River, the type locality of the Collón Curá Formation (Neuquén Province). Indeed, Roth (1899: 40) mentioned in the description of “ Icochilus ” endiadys that he had also found several fragments of mandibles and isolated teeth; however, he did not describe these specimens. Based on that, we infer that MLP 12-2887 and MLP 12-2916 are most likely associated with the MLP 12-2886 skull (holotype of “ Icochilus ” endiadys , see above). In addition, the finding of associated upper and lower dentitions in the sample herein presented (e.g., MLP 73-VII-7-1) allows us to recognize and describe the lower dentition for Protypotherium endiadys .

MLP 12-2887 comprises three fragments of mandible. In MLP 12-2887a ( Fig. 3A View Fig ), the canine is V-shaped and labiolingually flattened; p1 is mesially broken, wider than the canine ( Table 2); and p2 is similar to that of MLP 74-II- 1-4 from Río Negro. MLP 12-2887b is probably associated with MLP 12-2887a and comparable to MLP 12-2887c (left m1–2; Fig. 3C View Fig ). MLP 12-2916a and MLP 12-2916b ( Fig. 3B View Fig ) are very similar to MLP 74-II-I-4 ( Fig. 3F View Fig ; Table 2). In MLP 12-2916c, i1 has its tip broken and the base is circular in outline; i2 is proximally flattened and the outline of the base is circular, a shallow lingual sulcus divides the occlusal surface in a short mesial part and in a longer distal part. The p2–3 of MLP 12-2887a ( Fig. 3A View Fig ) have the talonid much more reduced in relation to the trigonid compared to Miocochilius anomopodus (UCPM 38409), where the difference in size is not so evident between trigonid and talonid, which are separated by a wider sulcus. Another difference is a simpler and more conical p 1 in MLP 12-2887a versus a larger and better developed p 1 in the Laventan specimen. The interatheres from Cerdas (Croft et al. 2009) differ from Protypotherium endiadys in having a more rudimentary p2 like in MLP 12- 2887a, and m3 lacks labial sulcus on the talonid (present in MLP 12-2887b and MLP 12-2916b).

The i1–2 are circular in outline, with i1 being more flattened laterally and smaller than i2 ( Fig. 3D View Fig ; Table 2); i3, in turn, is longer than i2 and compressed labiolingually ( Fig. 3D, E View Fig ; Table 2); the c is V-shaped, labiolingualy flattened and longer than i3 ( Fig. 3A, D, E View Fig ; Table 2). The i1–c are moderately procumbent. The mandibular symphysis has a triangular shape, very narrow at incisor level ( Fig. 3E View Fig ). The p1 is similar to the canine, but labially more convex with a shallow deeper lingual sulcus ( Fig. 3E View Fig ); p1 is overlapped by the canine ( Fig. 3D View Fig ).

The p2 of MLP 74-II-1-4 is a small version of p3–4 ( Fig. 3F View Fig ), with a narrower trigonid, reduced talonid, and shallower labial and lingual sulci. The same characteristics are present in the same tooth of MLP 90-IX-2-170. The p3–4 are larger and better developed than p2, mainly in the trigonid ( Fig. 3F View Fig ). The trigonid has a P-shaped outline with a very convex and inclined labial face, a concave distal face, and a smoothly undulated mesial face; the talonid, in contrast, is reduced and smaller than the trigonid. Labial and lingual sulci in p3–4 are deeper than in p2.

The m1–2 are indistinguishable from each other; they differ from p 3–4 in having a larger talonid, and deeper labial and lingual sulci ( Fig. 3F View Fig 1 View Fig , F 2 View Fig ); like p3–4, they have a P-shaped trigonid, but shorter in comparison; the talonid is triangular in outline, with the distal face concave at the point where it contacts the following trigonid tooth; in turn, the lingual face of the talonid is slightly concave. The m3 has a trigonid similar to that of m1–2, but differs from them in having a longer talonid, which is lingually and labially trilobed ( Fig. 3F View Fig 1 View Fig , F 2 View Fig ). In premolars and molars, the cement mainly covers labial faces and the enamel is lacking in the mesial face of the trigonid and in the distal face of the talonid ( Fig. 3F View Fig 2 View Fig ). The height of the horizontal ramus is nearly constant anteroposteriorly ( Fig. 3F 3 View Fig ).

Deciduous dentition and pattern of eruption: Unlike permanent dentition, deciduous teeth are low-crowned and develop roots. MLP 92-V-10-106d (DP2–4 and M1; Fig. 4A View Fig ) and MLP 92-X-10-119.40 (DP2–4) are very similar to each other ( Table 1). DP2–3 share with the permanent homologous teeth a deep mesial sulcus and a much folded ectoloph, but differ from them in being mesiodistally elongated and narrower ( Table 1). DP4, in turn, resembles a molar, with a rectangular outline, being larger than wide ( Fig. 4A View Fig 1 View Fig , A 2 View Fig ; Table 1); it has a lingual sulcus (instead of the mesially placed sulcus in DP2–3) dividing the tooth into two lobes, but the anterior lobe is much more reduced than the posterior lobe, contrasting with M1. The M1 of MLP 92-V-10- 106d is a not fully-erupted tooth, having one of the smallest dimension values of the sample ( Fig. 5 View Fig ); it has two very shallow and small fossettes, one in each lobe. MLP 92-X-10-119.38 ( Fig. 4C View Fig ) is also a juvenile specimen, but it is

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in a bit more mature stage than MLP 92-V-10-106d. MLP 92-X-10-119.38 has its P1, P2, and M1 fully erupted (but broken), and P3–4 are still inside the maxilla, with P3 being lower than P4 ( Fig. 4C View Fig ). In lateral view, we can observe the germ of P2 below DP2. It is interesting to note that MLP 92- X-10-119.38 corroborates that the sequence of eruption for permanent premolars is in posterior-anterior direction, from P4 to P2. A similar pattern was described for some notopithecids ( Vera and Cerdeño 2014), as well as for Oligocene and Miocene interatheres (Vera 2016; Vera et al. 2017).

Regarding lower dentition, MLP 92-V-10-106e comprises two fragments of mandible with right dp4–m1 ( Fig. 4B View Fig 1 View Fig , B 2 View Fig , B 5 View Fig ) and left dp3–4 ( Fig. 4B View Fig 3 View Fig , B 4 View Fig ). They are very probably associated with the MLP 92-V-10-106d maxillary fragment see above). The dp3 has a larger and more developed talonid than p3; in turn, dp4 has a molarized talonid, larger and wider than the talonid of p4, and its trigonid is longer and narrower than in m1. In MLP 92-V-10-106e, m1 is little worn; it has a shallow, long and narrow sulcus placed at the distolingual corner of the talonid, which quickly disappears with wear ( Fig. 4B View Fig 1 View Fig , B 2 View Fig ). Both MLP 92-V-10-106e and MLP 92-X-10-119.30 (m1–3) are juvenile individuals, showing smaller measurements for m1 ( Fig. 5 View Fig ; Table 2). The MLP 92-X-10-119.18 specimen has its p3 inside the bone and p4 nearly fully-erupted, corroborating that p4 erupts before p3, as it was described for upper teeth (see above). In addition, MLP 92-X-10-119.49 ( Fig. 4D View Fig ) has its p4 (partially broken) inside the bone, while m3 is erupting, indicating that dp4 is maintained throughout m3 eruption, such as happens in other interatheriines with a similar pattern of permanent premolar eruption (Vera 2016).

Appendicular skeleton: MAPBAR 1381 includes a distal fragment of left humerus, whose distal epiphysis (W, 19.5 mm; TD, 9.5 mm) is anteroposteriorly flattened and lateromedially enlarged ( Fig. 6A View Fig ). The ectepicondyle is incipient, whereas the entepicondyle is externally much expanded, having a well-developed supracondylar crest (rather broken) and a large entepicondylar foramen ( Fig. 6A View Fig 1 View Fig ). This configuration and the foramen are characteristics of Protypotherium australe (e.g., YPM-VPPU 015386, W, 18.2 mm; TD, 11.0 mm), but they are absent in Interatherium robustum (YPM-VPPU 015036). The medial crest of the trochlea is a prominent keel externally oriented and distally protruding ( Fig. 6A View Fig 3 View Fig ); in comparison, the capitulum is relatively small. The olecranon fossa is deep and there is a circular and small supratrochlear foramen, placed medially ( Fig. 6A View Fig 2 View Fig ). The coronoid fossa is not conspicuous. The deep trochlea, high medial crest, and supratrochlear foramen are features shared with Miocochilius anomopodus (UCMP 38091, W, 28.6 mm; T, 19.0 mm).

The left ulna MLP 73-VII-7-1 ( Fig. 6B View Fig ) is associated with upper and lower dentition. The olecranon (APD, 10.64 mm; TD, 6.13 mm; Fig. 6B View Fig 2 View Fig ) is proximally rough, laterally flattened, and medially curved; in lateral view, it has a rectangular outline. The trochlear notch is obliquely oriented with respect to the proximodistal axis; laterally, it forms a high and continuous border. The maximum diameter of the trochlear notch is larger than the olecranon length. The anconeal process is mediolaterally wide and has a robust border anterodistally pointed. The medial coronoid process is wide, robust, and anteriorly well expanded, while the lateral coronoid process is less developed in comparison ( Fig. 6B View Fig 1 View Fig ). The radial notch is subrectangular and slightly convex. In general terms, the morphology of MLP 73-VII- 7-1 agrees with the genus Protypotherium , although specific differences cannot be definitively established considering the fragmentary state of the bone; however, the ulna of P. endiadys has a less curved olecranon and a larger trochlear notch/olecranon ratio than P. australe (e.g., YPM-VPPU 015339, YPM-VPPU 015341).

The MLP 12-2916e right astragalus (L, 15.1 mm; Fig. 6C View Fig ) is associated with lower dentition. As in most interatheres, the lateral and medial crests of the trochlea (H, 8.5 mm; W, 6.4 mm) are vertical and parallel to each other, aligned with the axis of neck and head ( Fig. 6C View Fig 1 View Fig ). The articular surface of the trochlea narrows posteriorly and is less concave than in Protypotherium australe (YPM-VPPU 015077) or Miochochilius anomopodus (UCMP 37913). The sustentacular facet is convex and proximolaterally-distomedially oriented, covering most of the posterior face ( Fig. 6C View Fig 2 View Fig ). The head is broken.

Remarks.— Icochilus endiadys is the only species of the Interatheriinae formally described by Roth (1899) from the Collón Curá Formation in Neuquén Province. According to Roth (1899), I. endiadys exhibits cranial similarities to both I. extensus Ameghino, 1889 and the genus Interatherium , although Roth (1899) recognized it differs from them in its dentition, which resembles, in turn, that of Protypotherium praerutilum Ameghino, 1887 . In spite of that, Roth (1899) placed his species into the genus Icochilus Ameghino, 1889 , which was later synonymized with Interatherium ( Sinclair, 1909) ; both genera are under study at present (Fernández et al. 2015). Based on the restudy of the holotype of Icochilus endiadys (MLP 12-2886) plus the new material presented here and referred to the same taxon, we consider that the characteristics observed on these specimens are diagnostic of the genus Protypotherium instead of Interatherium (= Icochilus ), agreeing with Roth’s (1899) inclination.