Mammal teeth bring important information regarding phylogeny and diet. However, postcranial elements, although poorly studied for small Paleogene mammals, can provide other significant data. The purpose of this study is to associate tarsal bones with dental specimens for a systematic identification. We thus chose the Belgian locality of Dormaal (Tienen Formation, Belgium) that has yielded the earliest Eocene mammals of Europe. This particularly rich fauna, dated between 55.5 and 55.8 Ma, occurred during the Paleocene-Eocene Thermal Maximum, a key period in the mammal evolution. It is composed by archaic mammals (“condylarths”, arctocyonids, plesiadapiforms, “insectivorans”…) and also by earliest modern taxa (primates, rodents, carnivoraforms, artiodactyls …), representing about 14,000 dental specimens. 488 tarsal bones are studied according to three methods: morphology, relative abundance and relative size. 12 morphotypes of astragali and 18 of calcanei are discriminated and most of them are identified at the level of species (e.g. the marsupial Peratherium constans), genus or family (e.g. ischyromyid rodents). New perspectives in phylogeny and paleoecology are proposed for further studies implying tarsal bones.
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Dental remains of land mammals are sometimes discovered in shallow marine Paleogene deposits of the North Sea Basin. Such is the case for eleven specimens we describe here from the Early Eocene Egemkapel Clay Member in the middle part of the Tielt Formation, found in Ampe quarry at Egem in Northwestern Belgium. The small fauna consists of 6 taxa, including the neoplagiaulacid multituberculate Ectypodus, the erinaceomorph insectivore Macrocranion, the nyctitheriid Leptacodon, an eochiropteran bat possibly belonging to a palaeochiropterygid, an unidentified perissodactyl possibly belonging to an equoid, and a new species of the peradectid marsupial Armintodelphys. The latter represents the first European occurrence of the genus, which was previously only known from the North American late Early and early Middle Eocene of the Wind River and Green River basins in Wyoming and the Uinta Basin in Utah. Biogeographic and biostratigraphic analyses of peradectid marsupials suggest that Armintodelphys dispersed between North America and Europe around the time of the Early Eocene Climatic Optimum. The Egemkapel Clay Member has been dated as middle NP12, early late Ypresian, whereas the Egem mammal fauna can be correlated to the fauna of Avenay from the Paris Basin, which is the international reference-level MP8+9 of the mammalian biochronological scale for the European Paleogene.
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