Coyrou 1-2, une nouvelle faune de mammifères des phosphorites du Quercy, niveau intermédiaire (MP2O-21) proche de la "Grande Coupure"

Abstract

The Coyrou l-2 fauna, recently discovered in the Quercy Phosphorites, includes 25 species representing 12 families and 6 distinct orders (marsupials, insectivores, bats, primates, rodents and artiodactyls; Table 1). It is characterized by a Large diversity when one considers the relatively small fossil sample collected (fig. 1): each species is represented by only a few teeth, the most abundant forms being a rodent (Blainvillimys rotundidens: 42 specimens), an artiodactyl (Paroxacron sp.; 23 specimens) and a bat (Vaylatsia cf. prisca: 9 specimens). The components of the Coyrou 1-2 fauna are characteristic of the end-Eocene fauna normally seen in the Quercy (Level MP 19-20 in the mammalian biochronological scale), apart from an erinaceid irrsectivore (Tetracus nanus, represented by seven teeth) which forms part of the guild of Oligocene immigrants that arrived after the "Grande Coupure" (Stehlin, 1910). The association of Amphimeryx murinus, Necrolemur antiquus and Anoplotherium cf. latipes with Tetracus nanus has never been previously recorded. The presence of this characteristic Early Oligocene insectivore species in a fauna of essentially Eocene character suggests that the Coyrou 1-2 locality could be witness to an early arrival of a "Grande Coupure" immigrant. If this is the case, it indicates that the fauna would be very close to this event and would thus be slightly younger than MP 20, the last Eocene reference level in the mammalian biochronological scale of the Paleogene of Western Europe (see Schmidt-Kittler, ed., 1987). The evolutionary stages of the rodent species are hardly suitable for distinguishing the levels of this period, and so it is not possible to confirm or refute this chronological position close to the Eocene-Oligocene transition. Some very tenuous elements based on size variation among the bats and insectivores suggest a slightly younger age than that of the fauna of Escamps (MP 19), Pécarel (MP 19-20) and Tabarly (MP 20) among others. Numerical dating (Legendre and Bachelet, 1993) based on all the tooth elements with assigned lineages (see Table 1) gives an age intermediate between those of Escamps and Tabarly (MP 19 and MP 20, Late Eocene) and those of Ravet and Aubrelong 1 (MP 21, Early Oligocene) (Table 2). This hypothesis should enable an additional marker to be added to the MP 20 to MP 21 interval of the mammalian briochronological scale, thus refining the chronological resolution for the period around the "Grande Coupure" and the Eocene-Oligocene transition in the fauna of Western Europe. The Coyrou 1-2 locality thus completes the recent discoveries adding markers to the mammalian biostratigraphic scale (e.g. Legendre et al., 1992; Marandat et al., 1993) and confirms the biochronological value of the Quercy Phosphorites (Sudre et al., 1992).