The earliest Eocene Erquelinnes site was discovered in 1880, but its mammal fauna has been frequently ignored. This paper provides the first detailed overview of the Erquelinnes mammals since 1929. The new faunal list doubles the known diversity at Erquelinnes to a total of 16 species, now also including amphilemurids, hyaenodontids, mesonychids, louisinids, equids and diacodexeids. The majority of the Erquelinnes species is also present in the earliest Eocene Dormaal MP7 reference fauna, with as most notable exceptions the presence of a potentially dwarfed specimen of Dissacus, and of two perissodactyl taxa at Erquelinnes. The ceratomorph perissodactyl Cymbalophus cuniculus is also known from the earliest Eocene of England, but a specimen identified as cf. Sifrhippus sandrae is closely similar to contemporaneous primitive North American equids. This specimen represents the oldest unambiguous European equid and highlights faunal similarities between Europe and North America during this time interval. Faunal differences between Erquelinnes and Dormaal seem mostly due to depositional differences, and the Erquelinnes fauna represents a typical earliest Eocene fauna, closely similar to other MP7 and PEI faunas in Europe.
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Here we review the fossil record of European mesonychids, which are known only through the genera Dissacus and Pachyaena from Thanetian and Ypresian localities (from MP6 to MP10 reference-levels). We describe two new species, Dissacus rougierae, sp. nov., and Dissacus raslanloubatieri, sp. nov., respectively from Palette (Ypresian, ≈MP7) and from La Borie (Ypresian, ≈MP8 + 9). We also describe new specimens of D. europaeus from Berru (Thanetian, ≈MP6). The evolution of the geographic distribution of the European mesonychids is characterized by three phases: (1) the mesonychid Dissacus appeared in Europe during the Thanetian (≈ 57–58 Mya), probably due to dispersal from North America; D. europaeus survived the PETM event (≈ 56 Mya) and possibly experienced a dwarfism; (2) the large mesonychid Pachyaena migrated into Europe shortly after the Paleocene-Eocene boundary (≈ 55 Mya), but it was restricted to northwestern Europe, while Dissacus is recorded at this time only in southwestern Europe (Palette); and (3) Pachyaena rapidly disappeared from European environments, while Dissacus subsequently dispersed into northwestern Europe (≈ 54–52 Mya). We performed phylogenetic analyses in order to identify the relationships of the new species among mesonychids. It seems that the mesonychids went through two radiative events: the first during the Paleocene, the second mostly during the early Eocene. The first one corresponds to the diversification of Dissacus, while the latter resulted in the appearance of the most specialized mesonychids, such as Pachyaena and Mesonyx.
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RBINS Staff Publications 2017
