Critical analysis of carnivoran mammal success in Europe during the Paleogene

Why are we surrounded by only one group of placental carnivorous mammals (Carnivora: the present-day lions, dogs, bears, and seals among others) today, while at least three other groups of placental mammals (Hyaenodonta, Mesonychia, Oxyaenidae) were in competition with carnivorans 50 million years ago? Since the 1990s, palaeontologists have investigated the success of carnivoraform mammals (including Carnivora) and their crucial adaptations in detail. Analysis of the taxonomic and morphological diversification of these groups in the North American fossil record clearly showed that carnivoraforms outcompeted hyaenodonts and oxyaenids during the Eocene, specifically from around 50 Ma when carnivoraforms began to dominate. It has been suggested that the evolutionary success of carnivorans may have resulted from the broad range of dental adaptations (i.e., a broad variety of diets) conferred by the particular position of their carnassial teeth. Here we document the evolutionary history of the taxonomic diversity as well as the evolution of the body mass of carnivorous mammals that lived in Europe during the Paleogene (66–23 Ma). The results suggest that this competition was diametrically opposed in North America and Europe. Carnivoraforms actually did not become diversified in Europe during the Eocene and thus were not as taxonomically successful in Europe as in North America during that period. Moreover, when one considers body mass, the European hyaenodonts were distinctly more diversified than the carnivoraforms. The situation dramatically changed during the 'Grande Coupure' (around Eocene–Oligocene boundary; ca. 33.9 Ma). This transition corresponds to a major faunal turnover in Europe: during the earliest Oligocene global cooling (Oi-1) event, the Eocene endemic carnivorous fauna were replaced by immigrant taxa (hyaenodonts and carnivorans), mainly from Asia. The Oligocene fossil record shows a diversification of the carnivorans, whereas hyaenodonts were almost only represented by the hypercarnivorous genus Hyaenodon. However, two distinct periods can be discriminated in the Oligocene: the Rupelian was dominated by the Nimravidae and feliforms, while the Chattian was dominated by the caniformians (especially the Amphicyonidae and Ursidae). This turnover seems to be concomitant with the Latest Oligocene Warming and Microbunodon Event. Based on these results, one can hypothesize that the evolution of the European carnivorous mammals might have been profoundly driven by climate modifications (abiotic factors). Grant Information: This abstract is a contribution to the Belspo Brain Pioneer project BR/175/PI/CARNAGES funded by the Belgian Science Policy Office.

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Paleontology