1292
Journal of Paleontology 91(6):1272–1295
Biostratigraphic context.—Within Ameghino’s published work, all of his Archaeopithecidae members (excepting Guilielmoscottia, which was later transferred to notopithecids, see above), were described for the Casamayoran levels (Eocene) of the Sarmiento Formation (Patagonia). Ameghino usually differentiated specimens based on their origin, either from the ‘low’ or ‘upper’ sections of the Casamayoran, but unfortunately many of his specimens presently lack this important strati- graphic information. Cifelli (1985) recognized two distin- guishable sections in the traditional Casamayoran age, which later were referred to the Vacan and Barrancan subages. At present, the Vacan (the lower section or Cañadón Vaca Member, 43.1–46.9 Myr; Bellosi and Krause, 2014) and the Barrancan (the upper section or Gran Barranca Member, 42–39 Myr; Bellosi and Krause, 2014) are considered to be Lutetian- Bartonian, respectively (Woodburne et al., 2014a, 2014b, and references therein). In turn, all the specimens referred by Simpson (1967b) to Acropithecus rigidus come from the Casa- mayoran lower levels of Cañadón Vaca, which is the type locality of the Vacan subage (Cifelli, 1985). This locality is very near to ‘Oeste de Río Chico,’ which produced some of the Ameghino type specimens (Simpson, 1967a; Fig. 1). According to Simpson (1967a, p. 65), the assemblage from Cañadón Vaca is more similar to Ameghinos’ specimens from ‘Oeste de Río Chico’ than those from Colhué Huapi. In addition, many other specimens recognized here as Archaeopithecus rogeri derive from localities at Barrancan levels, such as Colhué Huapi (where the Cañadón Vaca section is absent; Bellosi and Krause, 2014), and are contemporaneous with the notopithecid remains. The specimens in the Egidio Feruglio collection, curated at the MGP, have information about locality, but the stratigraphic origin is not precise. Simpson (1935a, 1935b) referred to a Notopithecidae indet.
and ?Transpithecus sp. from Cañadón Hondo; however, Vera (2012a) determined that the specimen mentioned by Simpson (1935a) does not correspond to Transpithecus or any member of the notopithecid group (or any other specimen from the Cañadón Hondo fauna in the AMNH collection), and referred it instead to the archaeopithecid morphotype (AMNH FM 28534). This is the only fossil from Cañadon Hondo recognized as an archaeopithecid after several years of research and two visits to the AMNH. Particularly for the Cañadón Hondo area, Raigemborn et al. (2010) postulated that the Gran Barranca Member of the Sarmiento Formation is equivalent to the Cañadón Hondo Formation (Andreis, 1977) and that it overlies the Las Flores Formation. In turn, Bellosi and Krause (2014) proposed a correlation between the Cañadón Vaca Member (of the Sarmiento Formation) and the lower and middle sections of the Cañadón Hondo Formation, as well as between the Gran Barranca Member and the upper section of Cañadón Hondo Formation. This means that Simpson’sfossilfromCañadón Hondo (AMNHFM28534) could have come fromlevels younger than Itaboraian age. The same situations could apply to the specimens coming from the Bajo Palangana, and Cerro Blanco localities, where there are levels of both the lower section of the Sarmiento Formation (GranBarrancaMember) and theRío Chico Group (Riochican SALMA, late Paleocene–middle Eocene; Raigemborn et al., 2010, and references therein), but the stratigraphic origin of these specimens is unclear.
Concerning new records of archaeopithecids (Cladera et al.,
2004; Tejedor et al., 2009; Gelfo et al., 2010; and Bauzá et al., 2016), it is necessary to clarify some points. In the case of Acropithecus remains from the Las Violetas fauna, these were recovered from outcrops, uncomformably overlying the Las Violetas Formation (Gelfo et al., 2010), assigned to Las Flores Formation (RíoChico Group), and referred to early Eocene (Bauzá et al., 2016). In turn, the presence of Archaeopithecus in the fauna fromPaso del Sapo (Tejedor et al., 2009) is not discarded, bearing in mind that the Paso del Sapo fauna fills the gap between the Riochican SALMAandVacan subage (Woodbourne et al., 2014b; but see Krause et al., 2017); however, the taxonomic affinities of these remains need to be corroborated. Finally, if the record of Archaeopithecus in the Mustersan levels of Gran Hondonada (Cladera et al., 2004) is confirmed, it would imply the youngest record and the biochronological extension of this taxon. In sum, although Archaeopithecus rogeri is present in the
Cañadón Vaca and Gran Barranca members, it is more common in the Vacan than the Barrancan subage. The first (Riochican SALMA) and last (Mustersan SALMA) appearances proposed for Archaeopithecus still need to be confirmed (see discussion above).
Conclusions
This systematic revision of hundreds of specimens referred to archaeopithecids has permitted identifying only one morpho- type, which shows ontogenetic variation in both size and mor- phology, and intraspecific variability for some characters. Consequently, only one taxon is recognized among the many species originally described for the group. Nomenclatorial priority supports Archaeopithecus rogeri
as a valid name. In this sense, the names of all species described by Ameghino into Archaeopithecidae (Archaeopithecus alternans, A. rigidus, Acropithecus tarsus, and Ac. plenus) become synonymous with Archaeopitecus rogeri, including the combination Acropithecus rigidus proposed by Simpson (1967b). Regarding the lectotype (MACN-A 10824a) of Notopithecus fos- sulatus, this specimen is here recognized as an archaeopithecid; thus, the name N. fossulatus (and Archaeopithecus fossulatus sensu Simpson, 1967b) is considered synonymous with Archaeopithecus rogeri. In contrast to the other Casamayoran brachydont taxa, such
as notopithecids and oldfieldthomasiids, Archaeopithecus dis- plays incipient higher-crowned dentition, conical upper/lower incisors and canines, short diastemata between anterior teeth, a parastyle on P1, non-overlapping P/p1, hypocone developed on M3, non-procumbent lower incisors, a well-developed proto- stylid fold on p2–4, a reduced paralophid and well-developed entostylid on lower molars, and a deep hypoflexid on talonid of m3. Archaeopithecus shares the eruption sequence of permanent premolars and the well-developed entostylid on lower molars with notopithecids and Pleurostylodon, respectively. Some characters are polymorphic, such as presence/absence of the mesial cingulum and lingual sulcus on upper teeth. Addition- ally, Archaeopithecus teeth show variable occlusal morphology throughout ontogeny, which is associated with a wear-related variation in dental dimensions. With increasing wear, upper
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