New material of Diacodexis (Mammalia, Artiodactyla) from the early Eocene of Southern Europe - 08/08/18

Doi : 10.1016/j.geobios.2018.06.003

Myriam Boivin ^a, Maëva J. Orliac ^a,^⁎ , Miguel Antunes Telles ^b, Marc Godinot ^c, Yves Laurent ^d,^e, Bernard Marandat ^a, Dominique Vidalenc ^f, Rodolphe Tabuce ^a
^a Institut des Sciences de l’Évolution de Montpellier, c.c. 064, Université de Montpellier, CNRS, IRD, EPHE, place Eugène-Bataillon, 34095 Montpellier cedex 05, France
^b Academia das Ciencias de Lisboa, 19 Rua da Academia das Ciências, 1249-122 Lisbon, Portugal
^c EPHE, PSL et Sorbonne Universités - CR2P - MNHN, CNRS, UPMC-Paris 6, 75005 Paris, France
^d Muséum d’Histoire Naturelle de Toulouse, 35, allée Jules-Guesde, 31000 Toulouse, France
^e Association Paléontologique du Sud-Ouest, 13, chemin des Telles, 31360 Roquefort-sur-Garonne, France
^f 103, avenue F.-Mitterrand, 31800 St. Gaudens, France

^⁎Corresponding author.

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Abstract

Diacodexeidae are the first representatives of Artiodactyla in the fossil record. Their first occurrence is at the very base of the Ypresian (earliest Eocene, 56.0Ma) with Diacodexis, a genus well diversified during the early Eocene in Europe, especially during the MP7–MP8+9 interval. However, most of European species are documented by scarce material, retrieved from single localities. In this work, we describe new Diacodexis material from ∼MP7 and ∼MP8+9 localities of Southern Europe, including material of D. antunesi from Silveirinha, considered as the most primitive European Diacodexis species, and material from three localities from Southern France (Fordones, Palette, and La Borie). The new material documents Diacodexis premolar morphology and deciduous dentition which bear potentially important phylogenetic information, as well as astragali, including a specimen from Silveirinha that constitutes the earliest occurrence of an astragalus of the genus Diacodexis in the European fossil record. Investigation of the enamel microstructure reveals that early European species had a simple enamel pattern with one-layered Schmelzmuster composed of ‘basic’ radial enamel only, instead of the two-layered Schmelzmuster (thin radial enamel+thick layer of Hunter-Schreger bands) observed on North American species and so far considered to represent the primitive condition within Artiodactyla. In accordance with previous studies, our observations highlight that Diacodexis gigasei from Belgium is morphologically closer to the North American species D. ilicis than to D. antunesi from Portugal. The latter species, together with D. aff. antunesi from Fordones, appears to be morphologically closer to the Asiatic taxa D. indicus and D. pakistanensis. Finally, we found numerous similarities between D. cf. gigasei from Palette and D. gigasei, a result that challenges the intra-European provincialism that characterizes the earliest Ypresian. Diacodexis gigasei could be one of the rare species shared by the northwestern and southwestern European bioprovinces.