Vera—Eocene archeopithecids from Patagonia
than P4, hypocone lingually more developed than the protocone and both lingually separated by a deep sulcus. MACN-A 10813b is similar toMACN-A 10813a (Fig. 2.3) andMACN-A 10813c (Fig. 2.5). MACN-A 10813e (Fig. 2.7) shows very little wear; P2 has a low and reduced mesial cingulum and cannot be compared directly with MACN-A 10813a orMACN-A 10813c, but the premolars are similar to those of MACN-A 10813b as P3 has a deep lingual sulcus and P4 a clearly undulating ectoloph and high distal cingulum. The same is observed in MACN-A 10813f and MACN-A 10813i, where the P4s are comparable to those of MACN-A 10813b. In turn, MACN-A 10813d shows a more advanced stage of wear than MACN-A 10813b (e.g., M2 has protocone and hypocone united by entoloph), while MACN-A 10813h has a more developed mesial cingulum than MACN-A 10813b. All specimens in lot MACN-A 10813 can be considered as several individuals of the same taxon in different ontogenetic stages. Based on specimen MACN-A 10813b (Fig. 2.4), Simpson
(1967b) considered Archaeopithecus rigidus as a senior synonym of Acropithecus tersus; he proposed the combination Acropithecus rigidus, and also included Archaeopithecus alternans in the genus Acropithecus. Simpson (1967b, p. 65) incorporated in the hypodigm of Acropithecus rigidus several specimens from the AMNH collection (such as AMNH FM 28782,AMNHFM28884,AMNHFM28895), as well as seven partial mandibles with teeth, around 150 identified isolated upper cheek teeth and around 150 identified isolated lower cheek teeth (with no number or description). As stated by Simpson (1967b, p. 63–65), the differences
between Acropithecus and Archaeopithecus were based mainly on P1–3: Acropithecus has asymmetrically triangular premolars, a P1 longer than wide and a P2 less transverse; in contrast, Archaeopithecus has more transverse, more symmetrical and less pronounced ectoloph in P1–3. Interestingly, Simpson described the P2 of Acropithecus based on nine individuals in different stages of wear and mentioned a vertical groove immediately anteroexternal to the protocone and a sinuous protoloph; he also mentioned a mesial cingulum on the P2, on three of 23 P3s, and on 12 of 26 P4s; when present, the cingulum is very weak, evidencing a high variability in this character. The same features (lingual sulcus, mesial cingulum, and sinuous ectolophe) are observed on the premolars of MACN-A 10816 (holotype of Archaeopithecus rogeri; Fig. 2.1); in addition, the dimensions of MACN-A 10813e (Fig. 2.7) are similar to those of MACN-A 10816, and differences in transverse and ante- roposterior diameters are not significant between specimens (Table 1). This clearly demonstrates that both the specific differentiation between A. rogeri and A. rigidus proposed initi- ally by Ameghino (1901) and the generic distinction between
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Acropithecus and Archaeopithecus pointed out by Simpson (1967b) cannot be supported based on the dimensions and morphology presented here. According to the MACN catalogue, the type specimen of
Acropithecus tersus, MACN-A 10850 (Fig. 2.12–2.14), comes from Casamayoran levels of Patagonia. Lot MACN-A 10850 includes three upper molars, two left M3 (Fig. 2.12, 2.13) and one right M3 (Fig. 2.14), with disparity in wear stage and, hence, belonging to different individuals. Ameghino (1904, p. 204, fig. 231) figured the left M3s but identified them as M2–3 of the same individual. Simpson (1967b) considered the asso- ciation incorrect and synonymized the name Acropithecus tersus with Archaeopithecus rogeri, despite of the type specimen of the latter (MACN-A 10816; Fig. 2.1) has no M3 preserved. The left M3s MACN-A 10850 (Fig. 2.12, 2.13) are very similar to each other; they have a very reduced mesial cingulum and their lingual sulcus is mesially placed; in turn, the right M3 MACN-A 10850 (Fig. 2.14) has less wear than the previous molars (the lingual valley is open, separating proto- cone from hypocone) and the mesial cingulum is more devel- oped. The three molars have a trapezoidal outline and are comparable in morphology and size (Table 1) to the M3s of MACN-A 10813d (Fig. 2.6) and other specimens, such as AMNH FM 28782 (Fig. 3.3) and MMdP-M 727 (Fig. 4.1), so that that there is no enough evidence to consider a different species based only on these three upper molars (Table 1; Supplemental Data 3). Herein, indirect evidence (morphological and metrical similitudes between MACN-A 10850 and MACN-A 10813d, and between the latter and MACN-A 10816) allows establishing a comparison between Acropithecus tersus and Archaeopithecus rogeri, in agreement with the synonymy proposed by Simpson (1967b). As mentioned before, Ameghino (1903) transferred
Adpithecus plenus Ameghino, 1902 to the genus Acropithecus, establishing Acropithecus plenus. The specimen catalogued as the type of Adpithecus plenus has the number MACN-A 10851, which consists of a lot including a maxillary fragment with left M1–2 (here numbered MACN-A 10851a; Fig. 2.15) and a man- dibular fragment with very worn right m2–3 (MACN-A 10851b; Fig. 2.16). Adpithecus plenus, however, was described based on upper dentition (Ameghino, 1902, p. 8), which implies that the specimen MACN-A 10851a is actually the holotype of this species. Strong evidence for this assumption is the metrics ofM1 MACN-A 10851a (Table 1), which matches almost exactly with the dimensions provided by Ameghino (5.0×7.5mm). The mandibular fragment MACN-A 10851b does not belong to the same individual and, therefore, it is not part of the holotype; it is probably a different taxon. Besides, MACN-A 10851a shows morphologic (Fig. 2.15) and metrical (Table 1) similitudes with
Figure 2. Archaeopithecus rogeri.(1) MACN-A 10816, holotype: maxillary fragment with right P1–M2, occlusal view; (2) MACN-A 10815, holotype of Archaeopithecus alternans: maxillary fragment with left M1–3, occlusal and lingual views; (3–11) MACN-A 10813, material catalogued as type of Acropithecus rigidus:(3) MACN-A 10813a, maxillary fragment with left P2–M2; (4) MACN-A 10813b, maxillary fragment with left P4–M2; (5) MACN-A 10813c, maxillary fragment with right P4–M2; (6) MACN-A 10813d, maxillary fragment with right M1–3; (7) MACN-A 10813e, maxillary fragment with right P1–3?; (8) MACN-A 10813f, maxillary fragment with right P4; (9) MACN-A 10813g, maxillary fragment with right M1–2; (10) MACN-A 10813h, right M1 or M2; (11) MACN-A 10813i, left P4; (12–14) MACN-A 10850, material catalogued as type of Acropithecus tersus:(12, 13) two left M3 and (14) right M3, not associated, occlusal and lingual views; (15) MACN-A 10851a, holotype of Acropithecus plenus: maxillary fragment with left M1–2, occlusal view; (16) MACN- A 10851b, fragment with right m2–3, occlusal view; (17) MACN-A 10824a, holotype of Notopithecus fossulatus: mandible fragment with left p4–m1 and roots of p3 and m2, occlusal and labial views; (18) MACN-A 10824b, Notoungulata indet: mandible fragment with two extremely worn right teeth, occlusal and labial views. Abbreviations in the text. Scale bar is 5mm.
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