New material of Diacodexis (Mammalia, Artiodactyla) from the early Eocene of Southern Europe

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, 56.0 Ma) with the genus Diacodexis. Diacodexis is a well-diversified genus 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, 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 occurence 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 onelayered 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 in common between northwestern and southwestern bioprovinces.

A new basal raoellid artiodactyl (Mammalia) from the middle Eocene Subathu Group of Rajouri District, Jammu and Kashmir, northwest Himalaya, India

“…is therefore interesting and fills a gap in the evolution of early artiodactyls. While the order Artiodactyla is present since the earliest Eocene (56 Ma) with the diacodexeids Diacodexis ilicis in North America and D. gigasei and D. antunesi in Northern and Southern Europe, respectively (Estravis and Russell, 1989;Gingerich, 1989;Smith et al, 1996;Boivin et al, 2018), the earliest artiodactyls of the Indian subconti-nent are not recorded before 54.5 Ma with D. indicus and D. parvus from the Cambay Fm. in India (Bajpai et al, 2005;Kumar et al, 2010).…”

Small artiodactyls with tapir-like teeth from the middle Eocene of the Erlian Basin, Inner Mongolia, China

“…The lower jaw of Obotherium tongi is characterized by the convex ventral border and concave alveolar border, more similar to the arctocyonid Chriacus than to Diacodexis (Rose, 1996). The horizontal ramus of the lower jaw in Diacodexis is slender and shallow with a nearly straight ventral border, and becomes slightly shallower forwards (Boivin et al, 2018). A fragmentary lower jaw of Diacodexis indicus (GU 1622) with a convex ventral border and consistent height between m3 and m1 is unlike other specimens of the same species (Kumar et al (2010), the differences attributed to sexual dimorphism.…”

Paleoneurology of Artiodactyla, an Overview of the Evolution of the Artiodactyl Brain

“…Artiodactyls appeared quite abruptly in the fossil record ca. 55.8 Ma ago in the Holarctic, followed by an intense adaptive radiation in the early-middle Eocene (50-45 Ma; Theodor et al 2007, Rose et al 2012, Boivin et al 2018. Past generic diversity is at least seven times larger than today's, with more than 40 extinct families and nearly 950 fossil genera recognized (Janis et al 1998;Uhen 1998;Williams 1998;Uhen 2007;Gingerich 2010;Marx et al 2016).…”