Protypotherium Ameghino 1885

Genus Protypotherium Ameghino, 1885

(Figs 2–7; Supporting Information, Tables S1–S 2) 1882 Toxodontophanus Moreno, p. 23 (nomen nudum). 1885 Protypotherium Ameghino, p. 81 (original description). 1887a Toxodontophanus Ameghino, p. 64 (original description). 2018 Epipatriarchus Ameghino, 1904; Vera et al. p. 203. 2021a Eudiastatus Ameghino, 1901; Fernández et al. p. 882–883.

Type species: Protypotherium antiquum Ameghino, 1885, p. 81 –83 (original designation); Ameghino, 1889, pl. 15, fig.1, from Ituzaingó Formation, Entre Ríos Province, Argentina.

Included species: The type species, Protypotherium australe (Ameghino, 1887a); Pr.praerutilum Ameghin 1887b; Pr.claudum Ameghino, 1889, Pr. compressidens Ameghino, 1891b; Pr. columnifer Ameghino, 1902;

Pr. distinctum Cabrera and Kraglievich, 1931; Pr. minutum Cabrera & Kraglievich,1931; Pr.sinclairi Kramarz et al.,2015; Pr.colloncurensis Vera etal., 2017; and Pr.concepcionensis Solórzano etal., 2019.

Extended diagnosis: Medium to large-sized Interatheriinae. The rostrum is long and high as in Santiagorothia, Argyrohyrax, Miocochilius, and Federicoanaya; the postero-dorsal process of the premaxilla is present as in Santiagorothia, Argyrohyrax, and Caenophilus; the descending process of the maxilla poorly to moderately developed, in contrast to Cochilius, Interatherium, and Argyrohyrax, in which it is always more developed. The cheek teeth are euhypsodont unlike the protohypsodont Eopachyrucos, Santiagorothia, Proargyrohyrax, Argyrohyrax, Federicoanaya, and Brucemacfaddenia. The P/p3–4 are not molarized unlike many other interateriines that present some degree of molarization. The upper dentition is continuous in contrast to Interatherium, Miocochilius, Caenophilus, and some species of Cochilius. I1 is more developed than I2 as in Cochilius, Argyrohyrax, Miocochilius, Interatherium, and Brucemacfaddenia. The upper cheek teeth present a persistent lingual groove that separates the protoloph from the metaloph as in Neoicochilus, Archaeophylus, Choichephilum, Argyrohyrax, Miocochilius, Interatherium, Cochilius, Juchuysillu, and Progaleopithecus; these teeth also lack a mid-lingual lobe in contrast to Santiagorothia, Proargyrohyrax, Argyrohyrax, Cochilius, and Brucemacfaddenia. P3–4 are sub-triangular and longer than wide as in Caenophilus and Juchuysillu; they are smaller than M1–2, whereas they are similar in the remaining Interatheriinae; the entoflexus is mesially located as in Miocochilius, Juchuysillu, and Caenophilus. The i1–3 are imbricated and lack spaces between the teeth in contrast to Miocochilius and Patriarchus. The i1–2 are bifid and bicolumnar as in Federicoanaya and Progaleopithecus, whereas Cochilius, Argyrohyrax, Miocochilius, Interatherium, Proargyrohyrax, and Patriarchus exhibit a vertical lingual groove. The i1 exhibits a sub-cylindrical section in contrast to Cochilius, Argyrohyrax, and Interatherium, which show a sub-elliptical section, and Miocochilius and Patriarchus, in which it is highly expanded mesio-distally. The i3 is larger than i 2 in contrast to Cochilius, Miocochilius, Interatherium, and Patriarchus, in which these teeth are sub-equal. The dp1 lacks a differentiated talonid, as in Interatherium, Brucemacfaddenia, Juchuysillu, Federicoanaya, and Caenophilus. The lower molariforms exhibit the entoflexid opposite to the ectoflexid, whereas in Eopachyrucos, Santiagorothia, Proargyrohyrax, Argyrohyrax, and Brucemacfaddenia, the entoflexid is oriented distal to the ectoflexid. The p3–4 are smaller than the m1–2 as in Juchuysillu; these teeth lack a postmetacristid unlike Eopachyrucos, Proargyrohyrax, Santiagorothia, and Argyrohyrax; and the trigonid is longer than the talonid as in Eopachyrucos, Santiagorothia, Proargyrohyrax, Miocochilius, Federicoanaya, Juchuysillu, and Caenophilus. The m1–2 have the talonid longer than the trigonid unlike Eopachyrucos, Proargyrohyrax, and Santiagorothia, in which they are sub-equal; the talonid of m3 has a lingual groove unlike Cochilius and Miocochilius.

Occurrence: Late Oligocene to Late Miocene. Known from the Deseadan SALMA of Uruguay; the Deseadan, Colhuehuapian, Santacrucian, Colloncuran, ‘Mayoan’, Chasicoan, and Huayquerian SALMAs of Argentina; the Santacrucian, Friasian, and ‘Mayoan’ SALMAs of Chile; and the Huayquerian SALMA of Bolivia.

Description: Sinclair (1909) published an exhaustive description of Protypotherium, particularly of the skull and mandible. The most relevant dental characteristics of the (d)I/i1–(d)C/c and (d)P/p1–4 of this genus were described by Fernández et al. (2019, 2021a, b). To avoid redundancy, we discuss only the main characteristics of these teeth that justify the synonyms proposed here. However, the characteristics of M/m1–3 are described in detail in the following paragraphs.

Protypotherium has a complete dental formula, 3/3; 1/1; 4/4; 3/3. The dental arcade is generally continuous; there is a layer of cementum in the labial and lingual faces of each tooth, which is markedly reduced in the mesial and distal imbrication areas.

Upper permanent dentition: The upper cheek teeth are euhypsodont, with continuous enamel around the entire crown, being thinner at the mesio- and disto-labial angles; these teeth have a variable degree of imbrication. The upper premolars increase in size antero-posteriorly, but none of them reach molar proportions. The dP1 has a sub-cylindrical (e.g. MACN-A 9650 and YPM-VPPU 15386; Fig. 2A) to sub-elliptical (e.g. MACN-A 4049 and MPM-PV 4278; Fig. 2B–C) cross-section and the parastylar groove is of variable persistence, being superficial (e.g. AMNH 9187, MACN-A 3882, and MACN-A 3920) to persistent (e.g. MACN-A 4052, MPM-PV 4264, YPM-VPPU 15189, YPM-VPPU 15598, MACN-A 9521–9540); it can be mesially and distally imbricated by (d)C and (d)P2, respectively (e.g. MACN-A 3882, MACN-A 9623–9633, and MPM-PV 4278; Fig. 2D–E), only distally imbricated (e.g. AMNH 9187, AMNH 9226, AMNH 9260, MACN-A 4049, YPM-VPPU 15195, and YPM-VPPU 15643; Fig. 2F–G), or not imbricated at all (e.g. MACN-A 37, MLP 12-2886 and MPM-PV 4347; Fig. 2H–I).

M1–3 of Protypotherium differ from each other by their size, which generally decreases antero-posteriorly. Further M1–3 details are: the parastylar groove is, in general terms, superficial; the metacone is not completely individualized from the paracone, so the ectoloph is slightly undulated. The entoflexus is in the middle region of the tooth and it is transversally deep and persistent (i.e. vertically deep). It can be simple, this state being more common, or bifid; in fact, internal asymmetries concerning this feature have been identified, for example, in SGO.PV 21000, less M1–2 show a bifid entoflexus, whereas it is simple in right M1–2. The protoloph and metaloph are, in general terms, sub-equal in development and slightly lingually straight. M1–3 are longer than wide, and sub-rectangular in appearance. M3 presents the same characteristics as M1–2, except for the presence of the following: a more distally expanded metaloph, the length of which varies from poorly developed (e.g. MACN-A 3911 and MACN-A 1778; Fig. 2J–K) to highly developed (e.g. AMNH 9149 and MACN-A 4016; Fig. 2L–M); a metastyle evidenced by the presence of a conspicuous labial sulcus; and a rudimentary (e.g. MACN-A 1778, MACN-A 3911, and MLP 92-XI-18-31a; Fig. 2J–K) to moderately (e.g. MACN-A 9623–9633, MLP 91-IX-4-26, and YPM-VPPU 15386; Fig. 2A, E) excavated distal concavity or notch.

Lower permanent dentition: The permanent lower cheek teeth are euhypsodont. The p2–m3 are longer than wide; these cheek teeth are labially imbricated, so that the paralophid of the posterior cheek tooth overlaps the distal region of the hypolophid of the anterior tooth; in other words, the overlapping is the opposite to that of i1–dp1, which is lingual.

The m1–3 are morphologically similar to each other and, unlike the premolars, the talonid is longer than the trigonid, the former being P shaped and the laưer being sub-triangular. The mesio-lingual portion of the talonid can have a conspicuous concavity (e.g. Fig. 3A, F, L). The m3 presents the same characteristics as m1–2, except for exhibiting a longer talonid and having the lingual face always interrupted by a persistent groove of variable transversal depth: it can be shallow (e.g. MACN-A 3952; Fig. 3A), moderate (e.g. AMNH 9286 and MACN-A 11191a; Fig. 3B–C), or deep (e.g. MACN-A 3884 and MACN-A 9614; Fig. 3D). In contrast, the labial region can be smooth, without any groove (e.g. AMNH 9565 and MACN-A 1082; Fig. 3E–F), or it can present a groove mesially located with respect to the lingual sulcus, which can be superficial (e.g. AMNH 9149, MACN-A 3841, and MACN-A 3980, and MPM-PV 3531; Fig. 3G–H), moderate (e.g. MACN-A 532, MACN-A 3952, and MPM-PV 3739; Fig. 3I–J), or deep (e.g. MPM-PV 19612 and MLP 91-V-1-129; Fig. 3K). When the labial sulcus is present, the talonid is divided into two lobes, the anterior being rather rounded and more developed than the posterior (e.g. MACN-A 3952–3953, MACN-A 3955, MACN-A 3957–3958, MACN-A 3979, and MACN-A 11191b; Fig. 3L–M).