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| Ekgmowechashala in Rust, Ni, Tietjen & Beard, 2023. Artwork: Kristen Tietjen |
Abstract
Ekgmowechashala is a poorly documented but very distinctive primate known only from the late early Oligocene (early Arikareean) of western North America. Because of its highly autapomorphous dentition and spatiotemporal isolation, the phylogenetic and biogeographic affinities of Ekgmowechashala have long been debated. Here, we describe the oldest known fossils of Ekgmowechashala from the Brown Siltstone Beds of the Brule Formation, White River Group of western Nebraska. We also describe a new ekgmowechashaline taxon [Palaeohodites naduensis gen. nov. et sp. nov.] from the Nadu Formation (late Eocene) in the Baise Basin of Guangxi Zhuang Autonomous Region in southern China. Phylogenetic analysis suggests that North American Ekgmowechashala and the new Chinese taxon are sister taxa that are nested within a radiation of southern Asian adapiforms that also includes Gatanthropus, Muangthanhinius, and Bugtilemur. The new Chinese ekgmowechashaline helps fill the considerable disparity in dental morphology between Ekgmowechashala and more primitive ekgmowechashalids known from southern Asia. Our study underscores the fundamental role of southern Asia as a refugium for multiple primate clades during the cooler and drier climatic regime that prevailed after the Eocene–Oligocene transition. The colonization of North America by Ekgmowechashala helps define the beginning of the Arikareean Land Mammal Age and corresponds to an example of the Lazarus effect, whereby a taxon (in this case, the order Primates) reappears suddenly in the fossil record after a lengthy hiatus.
Keywords: Ekgmowechashalidae, Adapiformes, Eocene–Oligocene transition, Paleobiogeography, Dental evolution, Lazarus effect
Order Primates Linnaeus, 1758
Semiorder Strepsirrhini Geoffroy, 1812
Infraorder Adapiformes Hoffstetter, 1977
Family Ekgmowechashalidae Szalay, 1976
Included genera Ekgmowechashala Macdonald, 1963;
Bugtilemur Marivaux et al., 2001;
Muangthanhinius Marivaux et al., 2006;
Gatanthropus Ni et al., 2016;
Palaeohodites, gen. nov.
Subfamily Bugtilemurinae, subfam. nov.
Type genus Bugtilemur Marivaux et al., 2001.
Included genera Bugtilemur Marivaux et al., 2001;
Muangthanhinius Marivaux et al., 2006.
Diagnosis Differs from Ekgmowechashalinae in lacking highly crenulated enamel; lacking multiple neomorphic cusps and cuspules on upper and lower molars, including those identified as duplicated metaconule, duplicated protocone, ectostylids, and metastylids; and lacking large conules on upper molars.
Subfamily Ekgmowechashalinae Szalay, 1976
Included genera Ekgmowechashala Macdonald, 1963;
Palaeohodites, gen. nov.
Genus Ekgmowechashala Macdonald, 1963
Type species Ekgmowechashala philotau Macdonald, 1963.
Ekgmowechashala zancanellai Samuels et al., 2015.
Ekgmowechashala philotau Macdonald, 1963
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| Upper molar morphology in ekgmowechashaline primates, highlighting similarities and differences between Ekgmowechashala philotau from the Gering Formation, Nebraska, USA, and Palaeohodites naduensis from the Nadu Formation, Baise Basin, Guangxi Zhuang Autonomous Region, China. A, B) Ekgmowechashala philotau, isolated right M2 (KUVP 69859) in occlusal (A) and lingual (B) views. C, D) Palaeohodites naduensis, right maxillary fragment preserving M2 (IVPP V 32350) in occlusal (C) and lingual (D) views. |
Genus Palaeohodites gen. nov.
Etymology Combination of the Greek words palaios (ancient, old) and hodites (wanderer).
Type species Palaeohodites naduensis sp. nov.
Diagnosis Differs from Ekgmowechashala in having relatively longer and narrower P2–3, P2 roots more widely spaced, M1 with vestigial paraconid and large neomorphic cusp on central part of postvallid, M1–2 with hypoconid and hypoconulid clearly separate and cuspidate, and M2 without a continuous centrocrista and with closely connate lingual cusps. Differs from Gatanthropus and bugtilemurines in having heavily crenulated enamel, multiple neomorphic lower molar cusps, and duplicated protocone and inflated conules on M2.
Palaeohodites naduensis sp. nov.
Type locality Outcrop of the Nadu Formation located ∼1.5 km northeast of Quelin village, north-central Baise Basin, Guangxi Zhuang Autonomous Region, China (Fig. 2).
Age and distribution Late Eocene of the Baise Basin, Guangxi Zhuang Autonomous Region, China.
Etymology Named for the Nadu Formation, strata of which have yielded all known specimens of this species.
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| Illustration of Ekgmowechashala, the last primate to inhabit North America before humans. Artwork: Kristen Tietjen, scientific illustrator with the KU Biodiversity Institute and Natural History Museum. |
Kathleen Rust, Xijun Ni, Kristen Tietjen and K. Christopher Beard. 2023. Phylogeny and Paleobiogeography of the enigmatic North American Primate Ekgmowechashala illuminated by New Fossils from Nebraska (USA) and Guangxi Zhuang Autonomous Region (China). Journal of Human Evolution. In Press, 103452. DOI: 10.1016/j.jhevol.2023.103452
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