Mammal from the Eocene of Europe
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First palaeanodont (?pholidotan) mammal from the Eocene of Europe EMMANUEL GHEERBRANT, KENNETH D. ROSE, and MARC GODINOT Gheerbrant, E., Rose, K.D., and Godinot, M. 2005. First palaeanodont (?pholidotan) mammal from the Eocene of Europe. Acta Palaeontologica Polonica 50 (2): 209–218. We report the discovery in the early Eocene French locality of Le Quesnoy (MP7, Neustrian) of the first palaeanodont from the Eocene of Europe, and the first metacheiromyid from outside of western North America. The species, known from a dentary and a few postcranial bones, belongs to the genus Palaeanodon, and it is one of several North American immigrant taxa that characterize the Paleocene–Eocene faunal turnover in Europe. Palaeanodon sp. from Le Quesnoy is close in size to P. nievelti from the early Wasatchian of North America. However, it shows noticeable primitive features such as a more prominent ventral keel on the metacarpal III and a probably elongated and bilobed pc4 (= p4), although this is inferred from the infilled alveolus. Additional original features are also noticed on the tentatively referred astragalus. These minor differences suggest that the Le Quesnoy form represents a new species, but the available material remains in− adequate to name it. The morphology and the size of the metacarpal are actually closer to P. parvulus (Clarkforkian)—P. nievelti (Wasatchian) intermediates, suggesting a sister−group relationship with the latter (if Palaeanodon sp. from Le Quesnoy is not shown to belong to a distinct European lineage). This would indicate a dispersal at least as old as P. nievielti and a correlation of Le Quesnoy not later than early Wasatchian. The discovery of Palaeanodon in Le Quesnoy fits paleobiogeographically well with the hypothesis of a relationship of palaeanodonts to pholidotans, which have their earliest record in the middle Eocene of Europe (Messel). Key words: Mammalia, Palaeanodonta, paleobiogeography, Neustrian, Eocene, Le Quesnoy, Europe. Emmanuel Gheerbrant [[email protected]] (corresponding author) and Marc Godinot [[email protected]], EPHE, UMR−CNRS 5143 “Paleobiodiversité et Paléoenvironnements”, Case 38, Département Histoire de la Terre, Muséum national d’Histoire naturelle, 57 rue Cuvier, 75005 Paris, France; Kenneth D. Rose [[email protected]], Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine, 1830 East Monument Street, Baltimore, MD 21205, USA. Introduction this initial discovery, several postcranial bones from Le Quesnoy, probably belonging to the same palaeanodont spe− The locality of Le Quesnoy, from the early Eocene (MP7, cies, were identified (by KDR and MG). Neustrian Fahlbusch 1976 = Sparnacian of paleomammalo− Palaeanodonts are otherwise known mostly from the gists) of the Paris Basin (Oise, France), has yielded one of the Late Paleocene–Eocene of North America, with additional most diversified floristic and faunal assemblages from the marginal occurrences known in the early Oligocene of Eu− Paleogene (Nel et al. 1999). It provides a relatively unbiased rope (Heissig 1982; Storch and Rummel 1999) and in the picture of an early Eocene continental paleoecosystem. The early Eocene of Asia (Tong and Wang 1997). As a whole, mammal fauna from Le Quesnoy has been only briefly re− they are uncommon mammals, even if recent field work in ported. Here we describe an unexpected taxon, a metacheiro− NorthAmericahasshownthattheyarenotsorareasprevi− myid palaeanodont (see Fig. 1), previously reputed to be a ously thought (Gingerich 1989; Rose et al. 1991; Rose et al. relatively uncommon taxon of early Paleogene North Ameri− 1992). can mammal assemblages. Its discovery in Le Quesnoy pro− Institutional abbreviations.—MNHN, Muséum national vides additional evidence of the exceptional nature of its d’Histoire naturelle, Paris; UM, University of Michigan, fossiliferous assemblage in Europe. Museum of Paleontology, Ann Arbor, Michigan; USGS, In 1998, during the sorting of crocodilian and other un− U.S. Geological Survey collections, now at USNM; USNM, identified bones recovered from Le Quesnoy following our National Museum of Natural History, Smithsonian Insti− washing and screening operations of 1997 and 1998, one of tution, Washington, D.C. us (EG) identified a fragmentary lower jaw as that of a palaeanodont mammal, the first discovered in the Eocene of Other abbreviations.—MDE, Mammalian Dispersal Event; Europe. This record was mentioned in our preliminary paper NALMA, North American Land Mammal Ages; QNY, Le on the locality as “cf. Edentata indet.” (Nel et al. 1999). Since Quesnoy (Creil) France, QNY 2: channel 2 (see Nel et al. Acta Palaeontol. Pol. 50 (2): 209–218, 2005 http://app.pan.pl/acta50/app50−209.pdf 210 ACTA PALAEONTOLOGICA POLONICA 50 (2), 2005 50 mm Fig. 1. Reconstruction of the skeleton of Metacheiromys (modified by Rose and Emry 1993 after Simpson 1931: fig. 1), a palaeanodont from the Middle Eocene of North America. Palaeanodonta means “ancient edentate”, in reference to the highly reduced dentition (except for the large canines) in specialized genera such as Palaeanodon and Metacheiromys, which probably reflects a dietary preference for ants and termites. Palaeanodonts were digging and burrow− ing mammals thought to have been armadillo−like in their habits, and they are currently considered as the probable ancestors of the pangolins (Rose et al. 2005). 1999); UMR, Unité Mixte de Recherche. Lower case letters the postcanine tooth preserved in MNHN QNY 2−275 is are used to designate lower teeth (p = lower premolar; m = identified as pc5 (= m1). lower molar; pc = lower postcanine tooth). The pc5 has only one root and is typically peglike and small. It is signicantly smaller than its alveolus (Figs. 2A, 3A, B) as is usual in Palaeanodon. The crown is strongly Systematic paleontology worn by abrasion. Its occlusal outline is slightly oval with a mesio−distal long axis. Although the sharp rim of the abraded Order ?Pholidota Weber, 1904 crown suggests that enamel may have been present as seen in Alocodontulum (Rose et al. 1992), microscopic (SEM) ex− Suborder Palaeanodonta Matthew, 1918 amination reveals no evidence of enamel. Enamel was still Family Metacheiromyidae Wortman, 1903 present, though thin, on the cheek teeth of the epoicotheriid Genus Palaeanodon Matthew, 1918 Tubulodon (including Alocodontulum) (Jepsen 1932; Rose et al. 1991; Rose et al. 1992). Radiographic views (Fig. 3) show Palaeanodon sp. that the root is massive and robust, and longer than wide Figs. 2–6. (tranverse section oval). It is slightly recurved posteriorly. It Locality, horizon, and age: Le Quesnoy, Argiles à Lignites du Sois− is nearly four times higher than the worn crown. In lateral sonnais Formation, Early Eocene (MP7, Neustrian) of the Paris Basin, view the root appears only slightly narrower at its lower part France. than near the base of the crown. Referred material.—MNHN QNY 2−275, right fragment of The dentary preserves the distal edge of the alveolus of a dentary with the distal postcanine tooth. MNHN QNY 2−276, more anterior tooth, just where the lower jaw is broken (Fig. right metacarpal III. MNHN QNY 2−279, left first metatarsal I. 1A). The preserved vertical section of this alveolus indicates a Questionably referred material.—MNHN QNY 2−278, right tapered root. This tooth and pc5 are separated by an apparent astragalus. diastema. However, a cavity in this diastema suggests the rem− nants of the alveolus for the postcanine tooth pc4 (= p4), Description which is in the course of infilling by remodeled bone. The The dentary and lower dentition (Figs. 2, 3; Table 1).— Table 1. Dimensions of the dentary MNHN QNY2−275 (mm). MNHN QNY 2−275 is a fragment of right dentary preserving the distal part of the horizontal ramus and the posterior length width height postcanine tooth. The coronoid and angular processes, and pc5 1.4 0.8 ? the articular condyle are broken, as is typical of palaeanodont Alveolus 1.5 ? – dentaries. Only one tooth, the posterior postcanine, is pre− of pc4 served. 6.5 (to ascending Posterior ramus) – 8.2 The genus Palaeanodon, to which the Le Quesnoy speci− –– men is referred, has five postcanine teeth pc1–5 (e.g., based diastema (to medial but− on UM 66243, referred to P. cf. ignavus by Rose 1981). tress) 3.2 at pc5 – 3.9 5.2 below pc4 These teeth are interpreted as p1–4, and m1 by Secord et al. Horizontal – at medial and at medial (2002), implying that teeth were lost from the back of the se− ramus quence in metacheiromyids. Following this interpretation, buttress buttress GHEERBRANT ET AL.—EOCENE EUROPEAN PALAEANODONT 211 5mm (A–C) 1mm (D) Fig. 2. Palaeanodon sp., MNHN QNY 2−275, from Le Quesnoy, SEM micrographs. A–C. Right lower jaw in occlusal (A), lingual (B), and labial (C) views; mb, medial buttress; pd, posterior diastema; pc5, last lower postcanine tooth (= m1); alpc4, alveolus for pc4 (= p4); img, internal mandibular groove. D. Detail of the infilling alveolus of pc4 in occlusal view, showing its elongated and laterally compressed outline which is suggestive of an elongated p4 with bilobed root (or possibly two−roots). A, B, D, stereo micrographs. occlusal outline of this infilled alveolus is elongated (espe− them). However, most of the alveolus is completely filled by cially with respect to pc5), slightly constricted in its mid− bone of density similar to that of the rest of the jaw (e.g., length and it shows two small pits. This configuration suggests diastema area), confirming that the tooth was prematurely lost that the missing tooth (p4) was elongate and had a bilobed during the life of the animal. The identification of this tooth root, or just possibly was two−rooted. This is confirmed by the alveolus as that for pc4 in MNHN QNY 2−275 indicates that X−ray views, especially the lateral one (Fig. 3). In front of pc5, the anterior alveolus corresponds to pc3 (= p3). the occlusal surface of the dentary is depressed by a dou− The horizontal ramus is slender and shallow.