Filling a gap in the proboscidean fossil record: a new genus from the Lutetian of Senegal Rodolphe Tabuce, Raphaël Sarr, Sylvain Adnet, Renaud Lebrun, Fabrice Lihoreau, Jeremy Martin, Bernard Sambou, Mustapha Thiam, Lionel Hautier To cite this version: Rodolphe Tabuce, Raphaël Sarr, Sylvain Adnet, Renaud Lebrun, Fabrice Lihoreau, et al.. Filling a gap in the proboscidean fossil record: a new genus from the Lutetian of Senegal. Journal of Paleontology, Paleontological Society, 2019, pp.1-9. 10.1017/jpa.2019.98. hal-02408861 HAL Id: hal-02408861 https://hal.archives-ouvertes.fr/hal-02408861 Submitted on 8 Dec 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. 1 Filling a gap in the proboscidean fossil record: a new genus from 2 the Lutetian of Senegal 3 4 Rodolphe Tabuce1, Raphaël Sarr2, Sylvain Adnet1, Renaud Lebrun1, Fabrice Lihoreau1, Jeremy 5 E. Martin2, Bernard Sambou3, Mustapha Thiam3, and Lionel Hautier1 6 7 1Institut des Sciences de l’Evolution, UMR5554, CNRS, IRD, EPHE, Université de 8 Montpellier, Montpellier, France <[email protected]> 9 <[email protected]> <[email protected]> 10 <[email protected]> <[email protected] > 11 2Univ. Lyon, ENS de Lyon, Université Claude Bernard Lyon 1, CNRS, UMR 5276 12 Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement, F-69342 46 Allée d’Italie, 13 Lyon, France <[email protected]> 14 3Département de Géologie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop 15 de Dakar, B. P. 5005 Dakar, Sénégal <[email protected]> <[email protected]> < 16 [email protected]> 17 18 Running Header: A mid-Eocene proboscidean from Senegal 19 20 Abstract.— A long hiatus encompassing most of the Eocene (end of the Ypresian to the early 21 Priabonian) breaks up the proboscidean evolutionary history, which is otherwise documented 22 by a rich fossil record. Only two post Ypresian localities from West Africa (Mali and Senegal) 23 yielded scarce Moeritherium-like dental remains. Here, we study one of these remains from 24 Senegal and name a new genus, Saloumia. This taxon, confidently mid-Lutetian in age, evokes 25 Moeritherium and elephantifoms in view of its wrinkled enamel, the lack of centrocrista, and 1 26 its strong lingual cingulum. However, due to its pronounced bunodonty, which departs from 27 the bunolophodonty of both Moeritherium and elephantifoms, we cannot exclude that Saloumia 28 documents an early experiment in dental diversity among Paleocene-Eocene proboscideans, 29 without direct relationships with later proboscideans. 30 31 UUID: http://www.zoobank.org/0B6B83F8-817D-498C-A672-8FFA8F81A978 32 33 Introduction 34 35 Although the Afro-Arabian landmass has played a pivotal role in the evolutionary history of 36 early placental mammals (Werdelin and Sanders, 2010), the sub-Saharan Paleogene fossil 37 record remains very scarce, particularly in West Africa, where relatively little paleontological 38 work has been carried out. However, the potential to discover Eocene placentals was 39 demonstrated over half a century ago when a fragmentary proboscidean molar was described 40 from the middle Eocene (Lutetian) of M’Bodione Dadere, Senegal by Gorodiski and Lavocat 41 (1953). These authors compared this molar with those of Moeritherium, a genus from the late 42 Eocene-early Oligocene period. Interestingly, they correctly noticed that the M’Bodione 43 Dadere proboscidean was significantly smaller than all known Moeritherium species. Despite 44 this substantial morphological difference, Gorodiski and Lavocat (1953) were reluctant to 45 establish a new taxon based on this fragmentary molar, judging that Paleogene proboscideans 46 were too poorly known to substantiate the definition of a new taxon. At the time, early 47 proboscidean evolution was documented by just four genera, only known from the late Eocene 48 (Moeritherium and Barytherium) and early Oligocene (Moeritherium, Phiomia and 49 Palaeomastodon) of the Fayum, Egypt (e.g., Andrews, 1906; Osborn, 1936). After more than 50 fifty years of field research, the fossil record of stem proboscideans is now much better known 2 51 (Gheerbrant and Tassy, 2009; Sanders et al., 2010). Considerable progress has been made in 52 several other parts of Africa (Morocco, Algeria, Libya, Kenya, and Ethiopia) and the Arabian 53 Peninsula (Oman and Saudi Arabia), notably at the late Paleocene-early Eocene transition 54 (Gheerbrant et al., 1998a, 2005, 2012; Gheerbrant, 2009) and, to a lesser degree, at the late 55 Eocene-early Oligocene transition (Delmer et al., 2006; Delmer, 2009; Adnet et al., 2010; 56 Seiffert et al., 2012; Jaeger et al., 2012; Pickford 2015; Al-Kindi et al., 2017). 57 Despite these fundamental advances, some unresolved problems persist. Among them, 58 the origin and phylogenetic position of the genus Moeritherium remain uncertain. Two 59 phylogenetic scenarios have been recently proposed for the relationships of Moeritherium 60 within Proboscidea. First, according to Seiffert et al. (2012), Moeritherium could have a basal 61 position in the phylogeny, near Daouitherium and Numidotherium, two stem proboscideans 62 from the Ypresian of Morocco and Algeria, respectively. Second, Moeritherium has a more 63 elevated position in the phylogeny, being considered as the sister-group of the clade 64 Deinotheriidae-Elephantiformes (Seiffert, 2007; Delmer, 2009; Gheerbrant and Tassy, 2009; 65 Ferretti and Debruyne, 2011; Cooper et al., 2014). In any case, these contradictory scenarios 66 illuminate longstanding uncertainties regarding the transition from early proboscideans to 67 elephantiforms (palaeomastodonts and elephantoids). Particularly, the homology between the 68 lower incisors of early proboscideans and the ever-growing lower tusks of elephantiforms is 69 still debated (Delmer, 2009; Jaeger et al., 2012; Al-Kindi et al., 2017). 70 Current data suggest that the transition from early proboscideans to elephantiforms 71 occurred during the end of the Eocene (Priabonian) (Fig. 1a), but a simple examination of the 72 Paleogene proboscidean fossil record reveals geographical and temporal sampling biases in our 73 understanding of the evolutionary history of proboscideans. Earliest proboscideans are only 74 documented from Moroccan deposits, while other Paleogene species are known from few 75 African (e.g., Algeria, Egypt, Libya, Ethiopia, and Kenya) and Arabian sites (Saudi Arabia and 3 76 Oman). Most importantly, this history is largely truncated by a hiatus encompassing the end of 77 the Ypresian to the early Priabonian, so that the proboscidean fossil record is virtually unknown 78 during most of the Eocene (Sanders et al., 2010) (Fig. 1a). It is noteworthy that the group is 79 absent from the rich faunas from Gour Lazib (late early or early middle Eocene, Algeria), 80 Chambi (late early or early middle Eocene, Tunisia) and Namibia (?Lutetian-Bartonian) (e.g., 81 Adaci et al., 2016; Pickford et al., 2008). Proboscideans are also absent from the only two 82 unambiguous middle Eocene continental mammalian sites in Africa, i.e. the faunas of Aznag in 83 Morocco (Tabuce et al., 2005) and Mahenge in Tanzania (Kaiser et al., 2006). In contrast, the 84 only two ?mid-Eocene localities that yielded proboscidean remains were from West Africa. 85 Arambourg et al. (1951) described Moeritherium sp. from two isolated molars discovered from 86 marine sediments near In Tafidet, Mali (middle or late Eocene) (see Gheerbrant et al., 1998a 87 fig.6c; Delmer et al., 2006; O’Leary et al., 2006). Also from middle Eocene marine sediments, 88 Gorodiski and Lavocat (1953) described ?Moeritherium sp. based on the Senegalese molar here 89 studied. Since its initial description, this molar has never been figured; Domning (1986), 90 Gheerbrant et al. (1998a), and Delmer et al. (2006) briefly discussed its morphology and 91 concluded that it was too small to belong to a Moeritherium species. 92 In order to better document this peculiar Eocene proboscidean, we organized systematic 93 prospecting for fossil vertebrates at and around M’Bodione Dadere in 2010 and 2011. Although 94 we discovered a rich marine fauna represented by numerous sharks and rays, no additional 95 mammalian specimens have been discovered to the exception of an indeterminable minute 96 mammalian tooth fragment. Considering the difficulties to discover new specimens of 97 proboscideans in the rare Eocene Senegalese outcrops, we reassess the Moeritherium-like molar 98 from M’Bodione Dadere. Both its provenance (West Africa) and age (Lutetian) make this tooth 99 a pivotal asset to better understand the early history of proboscideans, as it fills an important 100 gap in their paleogeographic and chronological fossil record. 4 101 102 Geological setting 103 104 M’Bodione Dadere village is located north of the town of Kaolack in Sine-Saloum region, 105 central-western part of Senegal (Fig. 2). In this flat area, outcrops are absent due to an important 106 coverage of Quaternary to Recent sands (10-20 meters), which