The idea that fossil species (Buffon's " espèces perdues ", i.e., lost species) once existed was accepted between 1769 and 1778. This paradigmatic revolution in the Occidental culture was based on specimens found in North America. These specimens were studied by French and British anatomists, especially Daubenton. The fossils belong to the American mastodon, Mammut americanum (Kerr, 1792). The checking of the specimens housed in the Muséum national d'Histoire naturelle, Paris, allows to retrace the history of the earliest bones and teeth found in 1739 at Big Bone Lick, Kentucky, by the Indians who guided Longueuil's troupe on the way to New Orleans. The earliest molar ever figured (by Guettard in 1756), a lower third molar, m3, is identified for the first time since more than two centuries. Three molars were listed in 1764 by Daubenton as specimens found by Longueuil, and allocated to hippopotamus. Since Cuvier's statement in the early 19 th century, only two of the three (two upper second molars, M2), were thought to be housed in the Muséum. The third tooth (a lower second molar, m2), also housed in the Muséum, is identified. This tooth was previously considered as a gift sent to Buffon by Collinson, and different hypotheses are given to explain this dis-crepancy. The two other specimens, found by Longueuil and described in detail by Daubenton in 1764 as belonging to an elephant, were a femur and a tusk. The femur has always been on display in the Muséum. Only the tusk can be considered as lost. Finally, the status of the five molars figured by Buffon in 1778 is discussed, only three of them belong to the American mastodon. In conclusion, the m3 MNHN 1643 figured for the first time by Guettard (1756) is proposed to be selected as the lectotype of Mammut americanum.
Proboscidea, Mammalia, American mastodon, fossil species, Guettard, Daubenton, Buffon