Earliest Record of Rhinocerotoids (Mammalia: Perissodactyla) from Switzerland: Systematics and Biostratigraphy
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1661-8726/09/030489-16 Swiss J. Geosci. 102 (2009) 489–504 DOI 10.1007/s00015-009-1330-4 Birkhäuser Verlag, Basel, 2009 Earliest record of rhinocerotoids (Mammalia: Perissodactyla) from Switzerland: systematics and biostratigraphy DAMIEN BECKER 1 Key words: Rhinocerotidae, Amynodontidae, Hyracodontidae, Early Oligocene, north-central Jura Molasse, Switzerland ABSTRACT Earliest rhinocerotoids from Switzerland are reviewed on the basis of dental Epiaceratherium magnum and E. aff. magnum could indicate a new speciation remains from the earliest Oligocene north-central Jura Molasse localities of within the Epiaceratherium lineage around the top of MP22. The rhinocer- Bressaucourt (MP21/22) and Kleinblauen (top MP22). The record in Bress- otoid associations of Bressaucourt with Ronzotherium – Cadurcotherium on aucourt is restricted to Ronzotherium and Cadurcotherium, representing the western side of the southernmost Rhine Graben area, and Kleinblauen Switzerland’s oldest, well-dated post-“Grande Coupure” large mammal as- with Epiaceratherium – Ronzotherium – Eggysodon on the eastern side, re- sociation, the only occurrence of Cadurcotherium, and the earliest occurrence spectively, reveal a possible environmental barrier constituted by the Early of rhinocerotoids in Switzerland. The correlation with high-resolution stra- Oligocene Rhenish sea and its eventual connection with the Perialpine sea. tigraphy of this locality permitted a dating of the fauna to ca. 32.6 Ma, less This one could have separated an arid area in central-eastern France from than a million years after the “Grande Coupure” event. The rhinocerotoids of a humid area in Switzerland and Germany. These results, combined with the Kleinblauen are represented by Epiaceratherium, Ronzotherium and Eggyso- repartition of similar rhinocerotoid associations in Western Europe, also give don. With the presence of Plagiolophus ministri, they are the only well-dated new insights into an alternative earliest Oligocene dispersal route of rhino- Swiss post-“Grande Coupure” large mammal assemblage with the persistence cerotoids from Asia towards Western Europe via North Italy. of an endemic pre-“Grande Coupure” taxon. Moreover, the coexistence of Introduction out this time interval. The record is so far restricted to two “true” rhinocerotid genera with Epiaceratherium and Ronzo- Rhinocerotoids were the most flourishing perissodactyl mam- therium, and two rhinocerotoid genera with Eggysodon and mals during Tertiary times, especially in the late Middle and Cadurcotherium (Prothero 1993; Antoine et al. 2003). The Late Eocene of North America and Asia (e.g., Prothero & appearance of these rhinocerotoids together with other new Schoch 1989; Prothero 1993). The primitive sister taxon of the mammal families (e.g., Entelodontidae, Anthracotheriidae, three rhinocerotoid families (Amynodontidae, Hyracodon- Gelocidae, Cricetidae) coincides with the extinction/origi- tidae, Rhinocerotidae) was Hyrachyus (Prothero et al. 1986). nation event named “Grande Coupure” (e.g., Stehlin 1910; This cosmopolitan tropical forest-dwelling running form oc- Heissig 1987; Hooker 1987, 1992; Hartenberger 1998). The curred in Holarctic Early to Middle Eocene, when Eurasia calibration of calcareous nannoplankton and dinocyst zones formed one great landmass and North America was still con- with sequence stratigraphy in Italy, and an improved correla- nected to Europe across Greenland and to Asia via the Ber- tion between the Hampshire, Paris, and Belgian basins suggest ing Strait. By the Late Eocene, however, the main intercon- that this European faunal turnover corresponds to the time tinental connections were disconnected, and each continent interval of ca. 33.6–33.2 Ma (ca. 33.6–33.4 Ma in the Belgian developed its own endemic faunas (e.g., Prothero et al. 1986; Basin after Hooker et al. 2004, 2009; i.e., ca. MP20/21 bound- Prothero 1993). In Western Europe, apart from the occurrence ary of the European Mammal reference levels). After Hooker of Hyrachyus (e.g., Grauves, France; Geiseltal, Germany; see et al. (2004), it reflects a combined influence of both a global Aguilar et al. 1997), early rhinocerotoids occurred only in the climatic change (the Oi-1 cooling event of Zachos et al. 2001) earliest Oligocene and are still poorly documented through- and a major invasion of mammals from Asia, while the Euro- 1 Section d’archéologie et paléontologie, Office de la culture, République et Canton du Jura, Hôtel des Halles, CH-2900 Porrentruy 2, Switzerland. E-mail: [email protected] Earliest rhinocerotoids from Switzerland 489 Geological setting and taphonomy Basel In the north-central Jura Molasse, earliest Oligocene deposits Montbéliard are controlled by transgression–regression cycles of the Rhen- 2 ish sea. They belong to the Conglomérats de Porrentruy, Mee- Porrentruy Laufen ressand and Septarienton stratigraphical groups (Berger et al. 1 2005a, b; Picot et al. 2008). Whereas three transgression–re- gression cycles are known within the Rhine Graben during the Oligocene, only the first two are recorded in the Porrentruy region (Ajoie district), and only the second one in the Laufen 6.50° E basin (Fig. 2). Biostratigraphical data based on calcareous nan- G e r m a n y e c noplankton zones, dinoflagellate cyst zonation and mammal n a r Canton F reference levels allowed the dating of these marine incursions Jura (Picot et al. 2008). After Storni (2002) and Picot et al. (2008), Biel Switzerland the first recorded transgression corresponds to the biozone top N 47.05° N NP21–base NP22 (ca. MP21) in the Mulhouse area and the Ajoie basin. According to the dinocyst zonation of Simaeys et 0 10km al. (2005), the second one, the global Rupelian transgression, Rhine Graben Jura Molasse Plateau Molasse Folded Jura Tabular Jura A. Basal Rupelian B. Early Rupelian 1 Bressaucourt 2 Kleinblauen Top NP21 - base NP22 Base NP22 ca. MP 21 ca. MP21/22 Fig. 1. Geographical and geological setting of the Early Oligocene mammal localities Bressaucourt and Kleinblauen in the north-central Jura Molasse, northwestern Switzerland. pean and Asian continents fused again after the closure of the Turgai Strait. In the Molasse Basin, there is no high-resolution strati- graphic record across the “Grande Coupure”. The pre- and post-“Grande Coupure” faunas are reconstructed from iso- 1 lated short sections or fissure-fills. In Switzerland, the only pre- N N 7°E 20 km 7°E 20 km “Grande Coupure” faunas are the famous fissure-fills from 47°N 47°N Egerkingen (MP14; Brunet et al. 1987) and Mormont (MP16– C. Middle Rupelian Hercynian basement pre-uplift 19; Hooker & Weidmann 2000), whereas the earliest well-dated Top NP22 - base NP23 Eroded or not deposited post-“Grande Coupure” ones are dated to MP22 and limited to ca. MP22 small mammal assemblages (e.g., Balm; Engesser & Mödden Fluviatile 1997). Even though earliest Oligocene rhinocerotoid remains Lacustrine from Switzerland are known for a long time (Stehlin 1914; Salt lacustrine Heissig 1969; Uhlig 1999; Becker 2003) from the north-central Brackish Jura Molasse localities Bressaucourt (Canton Jura, northwest- Shallow marine ern Switzerland) and Kleinblauen (Canton Basel-Landschaft, Fan-deltas northwestern Switzerland), they are still poorly dated and the 1 Bressaucourt material is only partially reviewed (Fig. 1). The focus of the 2 Kleinblauen 2 Possible connection with present work is the first complete description of the specimens ? the perialpine sea from Bressaucourt (Ronzotherium filholi, Cadurcotherium Normal faults minus) and Kleinblauen (R. filholi, Epiaceratherium magnum, N 20 km 7°E Frontier E. aff. magum, Eggysodon osborni). New stratigraphical data 47°N ? from the north-central Jura Molasse (Picot et al. 2005, 2008) Fig. 2. Palaeogeographical maps of the southern Rhine Graben and the imply that these are the earliest occurrences of rhinocerotoids north-central Jura Molasse during the Early Oligocene (Fig. 2A–C), includ- and post-“Grande Coupure” large mammals from Switzerland, ing the two first transgression–regression cycles of the Rhenish sea (modified after Berger et al. 2005b and Picot et al. 2008). The mammal-bearing deposits and for this reason their palaeobiogeographical and palaeoen- of Bressaucourt were recorded during the transitional continental phase be- vironmental implications can be discussed from a new point tween the two marine incursions (Fig. 2B), and those of Kleinblauen during of view. the onset of the regression of the second incursion (Fig. 2C). 490 D. Becker simultaneously invaded the whole north-central Jura area dur- Abbreviations ing the NSO-2–NSO-3 (ca. top NP22–base NP23; ca. MP22). D, upper decideous tooth; I, upper incisive; C, upper canine; Its regression was clearly diachronous, occuring from NP23 to P, upper premolar; M, upper molar; d, lower decideous tooth; NP24 (ca. top MP22–MP23) in two directions, westwards and i, lower incisive; c, lower canine; p, lower premolar; m, lower northwards. molar; Mc, metacarpus; Mt, metatarsus; dext., right; sin., left; The Bressaucourt mammal locality near Porrentruy (Can- L, length; W, width; H, crown height; TD, transversal diam- ton Jura, northwestern Switzerland) was discovered by Choffat eter; APD, antero-posterior diameter; prox, proximal; dist, (1878), but he gave very little documentation about the outcrop. distal; dia, diaphysis. BSP, Bayerische Staatssammlung für Palä- The specimens are trapped in a calcarenitic matrix-supported ontologie und historische Geologie, Munich (Germany); IPHEP, gravel,