Vera—Eocene archeopithecids from Patagonia
maxilla P3–4; right Mc II-III, Mc IV?, left ulna, fragment of phalanx;AMNHFM144693, right dentary p4–m1;AMNHFM 144695, right maxilla P4–M2; AMNH FM 144696, right max- illaM2–3;AMNHFM144688, left dentary p4–m1;AMNHFM 144689, right dentary m2–3; AMNH FM 144690, left m1; AMNH FM 144691, right p3?; AMNH FM 144692, isolated and associated right M1, M2 and M3;AMNHFM144693, right dentary p4–m1; AMNH FM 144694, left m3; AMNH FM 144695, right maxilla P4–M2; AMNH FM 144696, right max- illa M2–3; MGP 29028, right dentary m2–3; MLP 75-II-3-19, left P4; MLP 75-II-3-20, left m1 or m2; PVL 162, left dentary p4–m1; PVL 163, left dentary m1–3; PVL 165, left dentary p4–m1; PVL 166, right dentary m1–2; PVL 167, right p4, alveolus c and i3; PVL 199, right p4?; PVL 210, right M2?; PVL 232, left m1?; PVL 242, left P3?. El Pajarito.—MLP 66-V-9-16, right P4?. Lomas Blancas.—AMNH FM 28886, right P4?. Las Cascadas.—MLP 93-XI-22-3, 22 lower teeth and 38
upper teeth, isolated; MLP 93-XI-22-16, 7 lower teeth and 12 upper teeth. Oeste Río Chico (Ameghino’s locality).—MACN-A
10813: a, left maxilla P2–M2; b, left maxilla P4–M2; c, right maxilla P4–M2; d, right maxilla M1–3; e, right maxilla P1–3; f, right maxilla P4; g, left maxilla M1–2; h, right M1?; i, left P4; MACN-A 10815, left maxilla M1–3; MACN-A 10831, right upper molar, left M1? and two right M3. Pico Salamanca.—MGP 31362, right maxilla M1–3. No locality data.—AMNH FM 15902c, right maxilla P4–
M1; MACN-A 10816, right maxilla P1–M2; MACN-A 10843, left lower molar; MACN-A 10847, left M3; MACN-A 10850, a-b) two left M3; c) right M3; MACN-A 10851a, left maxilla M1–2; MNHN-CAS 739, right maxilla P3–M2; MNHN-CAS 741, left m1; MNHN-CAS 751, right maxilla P4–M2. Occurrence.—Las Flores Formation (?56–47 Myr, early
middle Eocene; Krause et al., 2017) and Sarmiento Formation (Cañadón Vaca Member, 45–42 Myr, and Gran Barranca Member, 41.7–38.45 Myr, middle Eocene; Ré et al., 2010; Dunn et al., 2013; Bellosi and Krause, 2014; Krause et al., 2017). The fossiliferous localities with archaeopithecids are geographically located in Chubut Province, Argentina (Figure 1).
Description.—The following description for the cranium is
based on specimen AMNH FM 28782 (Fig. 3.1–3.6), an adult individual with associated skull and mandible and much worn dentition; although partially restored, it is the most complete individual known for archaeopithecids. As regards cranium size, the rostrum is short and high, but
the cranium is taller and the rostrum longer and taller than in Notopithecus (MACN-A 10787, MACN-A 10790); the dorsal profile rises backwards. The maxillary bone is concave on its rostral portion, in front of the orbit (Fig. 3.1). The infraorbital foramen is circular and large, placed above the P4 level. The orbits, posteriorly open, are very large in relation to the skull; their most anterior border is at M1–2 level, just behind the infraorbital foramen (Fig. 3.1, 3.2). Nasals are rectangular, narrow and long. The zygomatic arches are laterally high and apparently (by restoration) much expanded in dorsal view (Fig. 3.1). In ventral view, the most anterior part of the pre- maxillaries is semi-circular and its width increases slightly from
1285
I to P1 level; posteriorly, the palate is not significantly wider than the premaxillaries (Fig. 3.3, 3.4). Simpson (1967b, p. 61) noted that the jugal bone forms the external and anterior parts of the zygoma, continuing towards the lacrimal as a narrow splint, both different features from oldfieldthomasiids and notopithecids. Unfortunately, the poor preservation of AMNH FM 28782 does not allow differentiating main bones around orbital borders and defining the real extension of the lacrimal. The tympanic bullae are moderately sized in relation to cranium size, differing from other Eocene notoungulates such as Noto- pithecus, Oldfieldthomasia, and Colbertia. The mandibular bone is robust; its height increases gra-
dually backwards, from p2 (H = 10.1mm) to m2 (H = 15.1mm). The inferior border is convex up to m2–3 level, where there is a concavity, and after this point the height increases significantly (Fig. 3.6). The symphysis is very short and wide; its posterior border is at p2–3 level. There is a labial foramen below p2 and another one below talonid of p3. Concerning the teeth, Archaeopithecus has a complete,
rooted, brachydont (Fig. 3.3), but relatively higher-crowned dentition than other brachydont early notoungulates, such as notopithecids and oldfieldthomasiids. The enamel is continuous around the crown. Cementum is absent. The premolar series is longer than molar series, as in notopithecids; this ratio is characteristic of browser artiodactyls (Mendoza et al., 2002). No deciduous dentition was identified with certainly among the sample, probably because most of the sample corresponds to isolated teeth; thus, the following description refers to perma- nent teeth. The morphology and size of archaeopithecid teeth
are variable throughout ontogeny (Fig. 5.1–5.4), which led Ameghino to originally consider the presence of distinct species. The present revision and comparison of many archae- opithecid specimens permit establishing a wide intraspecific variation rather than interspecific differences, which was like- wise observed in archaeohyracids (Croft et al., 2003; Billet et al., 2009; Cerdeño et al., 2010) and other notoungulate groups (Francis, 1960; Madden, 1997; Billet et al., 2008; Cerdeño et al., 2008). Indeed, Simpson (1967b) also recognized a highly variable morphology on crown pattern and dimensions in the archaeopithecid teeth samples he studied, such as the extremely variable mesial cingulum in premolars and molars. In Archaeopithecus, the upper teeth (mainly molars) are labiolingually narrow at occlusal level (TD ≈ MDD), but the transverse diameter increases to the base, modifying the dimensions on the tooth (TD>MDD). Another peculiarity is that the presence of mesial cingulum and the lingual and mesial sulci are variable in the upper dentition of archaeo- pithecids. Upper dentition.—The I1–3 of AMNH FM 28782 are
cylindrical in outline (Fig. 3.4). I1 is the greatest incisor (2.6 × 2.4mm) and differs from the other incisors in having a labiolingualy flattened tip and a lingual wear facet; I2 (2.0 × 2.2mm) is a bit less compressed than I1 and the wear facet is less developed; I3 (2.4 × 2.0mm) is conic, pointed, and has two smooth facets on the mesial and distal sides. The canine in AMNH FM 28782 is broken at alveolar level, but the preserved crown fragment indicates a cylindrical tooth, with approxi- mately the same diameter as I3. There are short diastemata
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