Journal of Paleontology, 91(6), 2017, p. 1272–1295 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.53 Patagonian Eocene Archaeopithecidae Ameghino, 1897 (Notoungulata): systematic revision, phylogeny and biostratigraphy Bárbara Vera Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CONICET-Mendoza, Ruiz Leal s/n, 5500 Mendoza, Argentina, 〈[email protected]〉 Abstract.—The Archaeopithecidae is a very poorly known group of native ungulates from the Eocene of Patagonia (Argentina), whose alpha taxonomy has remained obscure since Ameghino’s times. It is traditionally considered as a family representative of the Casamayoran (middle Eocene) South American Land Mammal Age, and is thought to be morphologically close to the notopithecids. After studying >200 specimens from several institutions, including all the type specimens, a taxonomic overestimation is established. Out of the six species considered originally as archaeopithecids, Archaeopithecus rogeri Ameghino, 1897 is here recognized as the only valid name and species; subsequent synonymies are proposed and previous taxonomic hypotheses discarded. This exhaustive revision has permitted improving the knowledge of A. rogeri and, for the first time, it has revealed many craniodental characters, which allow amending its diagnosis and differentiating this taxon from other Eocene notoungulates. Archaeopithecus rogeri is a small-sized taxon characterized by its complete and rooted dentition, which is relatively higher than that of other contemporaneous short-crowned notoungulates and shows ontogenetic variation in size and morphology. The body mass range of A. rogeri (1.4–2.5 kg) is comparable to those of notopithecids and some small hegetotheriids. The phylogenetic analysis shows A. rogeri is not directly related to any family within Notoungulata, appearing into a polytomy, as a basal taxon of typotherians. The biochronological range of A. rogeri is adjusted to Vacan (middle Eocene) through Barrancan subages (late middle Eocene); older (Riochican, late early Eocene) and younger (Mustersan, late Eocene) records remain to be confirmed. Introduction family in the Prosimiae, just as did with the family Notopithe- cidae Ameghino, 1897. The archaeopithecids are a group of small native ungulates, Later, Ameghino (1901) described the species typically representative of the Casamayoran South American Archaeopithecus alternans and A. rigidus, the genus Ultra- Land Mammal Age (SALMA; Ameghino, 1906; Simpson, pithecus with two species (U. rutilans and U. rusticulus), and 1945, 1967b; Marshall et al., 1983; Cifelli, 1985) and known the species Guilielmoscottia plicifera, and placed them presently only from Chubut Province, Patagonia (Argentina). within Archaeopithecidae. In a subsequent work, Ameghino However, there are a few older (Riochican SALMA) and (1903) described the genus Acropithecus and its type species younger (Mustersan SALMA) records, yet to be confirmed, that A. tersus, and placed it in the family Notopithecidae. Con- could modify first and last appearances (see below). Little is currently, he transferred to Acropithecus the species Adpithecus known about this group—its systematic background is compli- plenus Ameghino, 1902, previously described within notopithe- cated, being frequently related in the literature and collections cids. Thus, the genus Acropithecus sensu Ameghino, 1902, to notopithecids, which is another Patagonian group of Eocene comprised two species: A. tersus and A. plenus.According notoungulates that recently has been revised (Vera, 2013b, to one of his last contributions, Ameghino (1906) listed 2016). This emphasizes the difficulty in differentiating archae- among the ‘Notostylopense fauna’ (Casamayoran SALMA) both opithecids from notopithecids based on dental morphology, Archaeopithecus and Acropithecus, and placed them in the as well as from other taxa such as Oldfieldthomasiidae or Archaeopithecidae and Notopithecidae, respectively. Henricosborniidae, or an “oldfieldthomasiid-archaeopithecid- Schlosser (1923) transferred Guilielmoscottia to Noto- notopithecine complex” as Simpson (1967b, p. 63) expressed. pithecidae, which was accepted by Roth (1927), Simpson (1936, The concept of family Archaeopithecidae was created 1945, 1967b), and Scott (1937); however, Ultrapithecus was by Ameghino (1897) based on the genus and species considered to be a member of the Oldfieldthomasiidae and Archaeopithecus rogeri, including also the monotypic genus Pachypithecus a nomen dubium by Simpson (1967b, p. 246). Pachypithecus and its species P. macrognathus Ameghino, Scott (1937) regarded Archaeopithecus as a member of the 1897. According to Ameghino, Archaeopithecidae shared some Notopithecidae, but provided no justification. features with primates, such as brachydont dentition and a Simpson (1967b, p. 64) argued that Ameghino’s original primate-like jaw, which he cited as a reason to consider this definitions for Notopithecidae and Archaeopithecidae were not 1272 Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.226, on 27 Sep 2021 at 21:07:47, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/jpa.2017.53 Vera—Eocene archeopithecids from Patagonia 1273 substantive, and stated that Notopithecus Ameghino, 1897 Toxodontia as it shared numerous notoungulate characters with (type genus of the family Notopithecidae) and Archaeopithecus Archaeohyracidae and Oldfieldthomasiidae. Later, the analysis (type genus of the family Archaeopithecidae) could not be by Reguero and Prevosti (2010) places Archaeopithecidae close distinguished based on Ameghino’sdefinitions for the two to Oldfieldthomasiidae, both excluded from Typotheria and, groups. Despite this, Simpson stated that Archaeopithecus was thus, in partial agreement with Simpson’s (1945) criterion. closer to Acropithecus and should be in the same family, Then, in Billet’s (2011) analysis, Acropithecus forms part of a but separated from Notopithecus, therefore he transferred large basal bush branching out into the oldfieldthomasiids Acropithecus to Archaeopithecidae. Oldfieldthomasia, Colbertia and Ultrapithecus; the genus According to Simpson (1967b), Archaeopithecus is similar Campanorco; the Interatheriidae; and a clade uniting the to Acropithecus, and their generic differences rely on the Archaeohyracidae, Mesotheriidae and Hegetotheriidae. More anterior upper premolars. Simpson (1967b) argued that in recently, a revision of the subfamily Notopithecinae (sensu Archaeopithecus the premolars, and most notably P1–2, are Simpson, 1945, 1967b) yields novel taxonomic modifications more transverse and symmetrical, the ectoloph columns are less for this group (Vera, 2012a, 2012b, 2013a, 2013b; Vera and pronounced, and P1 is markedly wider than long. In Cerdeño, 2014), including the Archaeopithecidae. For the latter, Acropithecus, P1 is longer than wide and P2 is less transverse Vera (2013b) hypothesizes an overestimation in the number of than in Archaeopithecus, the P1–2 are asymmetrically trian- species and preliminarily proposes two monospecific genera. gular, and the ectoloph columns are strong (see below). Finally, Vera (2016) considers Acropithecus rigidus as the Simpson (1967b) had hundreds of specimens of Archae- sister taxon of Typotheria sensu Reguero and Prevosti (2010), opithecidae available for study as a result of the Scarritt which includes the notopithecid clade, but she disagrees with Patagonian Expeditions (1930–1933 and 1933–1934), includ- the hypothesis of these authors grouping A. rigidus with ing the better-preserved specimen. Strikingly, he neither figured Oldfieldthomasia; in the minority of topologies (Vera, 2016, any of them nor provided any descriptions, in contrast to what fig. 2B), Acropithecus rigidus is nested into the notopithecid he did for notopithecids (Simpson, 1967b, figs. 22–28). Many of clade as the sister taxon of Guilielmoscottia plicifera and these specimens still lack a catalogue number, and remain Transpithecus obtentus. Based on morphological characters, labeled only with a field number in some cases, which may Vera’s (2016) analysis was the first to suggest a possible link explain why Simpson did not include them in his systematic between archaeopithecids and notopithecids from a phyloge- work. netic point of view. From the most complete specimen, AMNH FM 28782 In this paper, the type material and many other specimens (partial skull and associated mandible), Simpson (1967b) incor- of archaeopithecids from several institutions are subjected to an porated substantial systematic changes into the family Archae- exhaustive revision in order to determine the alpha taxonomy opithecidae, with the following nomenclatural actions: (1) he and provide robust diagnoses. This work sheds light on the transferred Archaeopithecus rigidus to the genus Acropithecus, systematic of the group and enables and concrete discussions of establishing the combination Acropithecus rigidus (Ameghino, biostratigraphic issues, geographic distribution and phyloge- 1901) and assigning AMNH FM 28782 to A. rigidus;(2)he netic relationships with respect to other groups. In addition, the considered Archaeopithecus alternans and Acropithecus tersus large sample of archaeopithecid specimens allows for a body synonymous names of Acropithecus rigidus; and 3) he transferred mass estimation and for inferring ecological attributes. Notopithecus fossulatus Ameghino, 1897 to the genus