Vera—Eocene archeopithecids from Patagonia
substantive, and stated that Notopithecus Ameghino, 1897 (type genus of the family Notopithecidae) and Archaeopithecus (type genus of the family Archaeopithecidae) could not be distinguished based on Ameghino’sdefinitions for the two groups. Despite this, Simpson stated that Archaeopithecus was closer to Acropithecus and should be in the same family, but separated from Notopithecus, therefore he transferred Acropithecus to Archaeopithecidae. According to Simpson (1967b), Archaeopithecus is similar
to Acropithecus, and their generic differences rely on the anterior upper premolars. Simpson (1967b) argued that in Archaeopithecus the premolars, and most notably P1–2, are more transverse and symmetrical, the ectoloph columns are less pronounced, and P1 is markedly wider than long. In Acropithecus, P1 is longer than wide and P2 is less transverse than in Archaeopithecus, the P1–2 are asymmetrically trian- gular, and the ectoloph columns are strong (see below). Simpson (1967b) had hundreds of specimens of Archae-
opithecidae available for study as a result of the Scarritt Patagonian Expeditions (1930–1933 and 1933–1934), includ- ing the better-preserved specimen. Strikingly, he neither figured any of them nor provided any descriptions, in contrast to what he did for notopithecids (Simpson, 1967b, figs. 22–28). Many of these specimens still lack a catalogue number, and remain labeled only with a field number in some cases, which may explain why Simpson did not include them in his systematic work.
From the most complete specimen, AMNH FM 28782
(partial skull and associated mandible), Simpson (1967b) incor- porated substantial systematic changes into the family Archae- opithecidae, with the following nomenclatural actions: (1) he transferred Archaeopithecus rigidus to the genus Acropithecus, establishing the combination Acropithecus rigidus (Ameghino, 1901) and assigning AMNH FM 28782 to A. rigidus;(2) he considered Archaeopithecus alternans and Acropithecus tersus synonymous names of Acropithecus rigidus; and 3) he transferred Notopithecus fossulatus Ameghino, 1897 to the genus Archae- opithecus, establishing (with some doubt) the combination ?A. fossulatus. In summary, after Simpson (1967b), the family Archaeopithecidae comprised the genus Archaeopithecus with two species, A. rogeri (type species) and ?A. fossulatus (Ameghino, 1897), and the genus Acropithecus with a single species, A. rigidus. Under this late name Acropithecus rigidus, Simpson (1967b) placed most of the specimens recovered by the Scarritt Patagonian Expeditions at Cañadón Vaca, Chubut Province (Argentina), which belong to the AMNH collection. Since Simpson’s work (1967b), the members of this group
have not been subjected to systematic revision or other detailed studies, and Acropithecus rigidus is practically the only species considered in subsequent studies including Archaeopithecidae (Cifelli, 1985, 1993; Hitz et al., 2006; Reguero and Prevosti, 2010; Reguero et al., 2010; Billet, 2011; Elissamburu, 2012; Vera, 2016), most likely because the specimens of Acropithecus are represented by much more complete material that the type of Archaeopithecus. From a phylogenetic point of view, the family Archae-
opithecidae was regarded as a member of suborder Typotheria (Simpson, 1931, 1967b; Scott, 1937; Mones, 1986; Cifelli, 1993; Billet, 2011), but Simpson (1945) placed it into suborder
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Toxodontia as it shared numerous notoungulate characters with Archaeohyracidae and Oldfieldthomasiidae. Later, the analysis by Reguero and Prevosti (2010) places Archaeopithecidae close to Oldfieldthomasiidae, both excluded from Typotheria and, thus, in partial agreement with Simpson’s (1945) criterion. Then, in Billet’s (2011) analysis, Acropithecus forms part of a large basal bush branching out into the oldfieldthomasiids Oldfieldthomasia, Colbertia and Ultrapithecus; the genus Campanorco; the Interatheriidae; and a clade uniting the Archaeohyracidae, Mesotheriidae and Hegetotheriidae. More recently, a revision of the subfamily Notopithecinae (sensu Simpson, 1945, 1967b) yields novel taxonomic modifications for this group (Vera, 2012a, 2012b, 2013a, 2013b; Vera and Cerdeño, 2014), including the Archaeopithecidae. For the latter, Vera (2013b) hypothesizes an overestimation in the number of species and preliminarily proposes two monospecific genera. Finally, Vera (2016) considers Acropithecus rigidus as the sister taxon of Typotheria sensu Reguero and Prevosti (2010), which includes the notopithecid clade, but she disagrees with the hypothesis of these authors grouping A. rigidus with
Oldfieldthomasia; in the minority of topologies (Vera, 2016, fig. 2B), Acropithecus rigidus is nested into the notopithecid clade as the sister taxon of Guilielmoscottia plicifera and Transpithecus obtentus. Based on morphological characters, Vera’s (2016) analysis was the first to suggest a possible link between archaeopithecids and notopithecids from a phyloge- netic point of view. In this paper, the type material and many other specimens
of archaeopithecids from several institutions are subjected to an exhaustive revision in order to determine the alpha taxonomy and provide robust diagnoses. This work sheds light on the systematic of the group and enables and concrete discussions of biostratigraphic issues, geographic distribution and phyloge- netic relationships with respect to other groups. In addition, the large sample of archaeopithecid specimens allows for a body mass estimation and for inferring ecological attributes.
Materials and methods
Descriptions and comparisons are based on personal observa- tions of ~215 catalogued specimens of archaeopithecid from several institutions (see below), including the type material of the Ameghino collection, and the Scarritt Pocket and Egidio Feruglio collections. These specimens come from different localities of Chubut Province, Argentina (Fig. 1) and they are detailed below. To facilitate the description and comparison, each speci-
men forming part of a lot is indicated with a letter accompanying the catalog number, particularly for the type specimens from the Ameghino collection. The term Casamayoran SALMA is used in the traditional sense to include the Vacan and Barrancan subages. The mesiodistal and labiolingual diameters for each tooth
were taken at occlusal level with a digital caliper to the nearest 0.1mm. Each specimen was assigned to one of three wear stages (based on upper and lower cheek molars features): little wear, moderate wear and heavy wear (see Description). It should be noted that this procedure became subjective and difficult when assigning a particular wear stage to an isolated teeth, which
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