Abstract: The status of the various species of Libycosaurus (Anthracotheriidae, Artiodactyla, Mammalia) has become extremely complicated following the initial identification of the type species as a dinosaur [Bonarelli, G., 1947. Dinosauro fossile del Sahara Cirenaico. Rivista di Biologia Coloniale, Roma 8, 23–33.]. The first reviser [Black, C., 1978. Anthracotheriidae, in: Maglio, V.J., Cooke, H.B.S. (Eds.), Evolution of African Mammals, Harvard University Press, Cambridge, pp. 423–434.] of the type species Libycosaurus petrocchii unknowingly switched the holotype which is small, for a much larger specimen, an error that passed unnoticed until the present study was undertaken. In his initial description of the type species, L. petrocchii, Bonarelli (1947) provided approximate measurements of the length and breadth of the type specimen from Sahabi, Libya, but these bear no relation to the reductions indicated in the figure captions, which suggest a much larger animal some 1.6 to 1.8 times bigger. In this paper the decision to accept the measurements rather than the figure captions is based on the writings of [Petrocchi, C., 1943. Il giacimento fossilifero di Sahabi. Collezione Scientifica e Documentaria a cura del Ministero dell’Africa Italiana 12, 1–167. Petrocchi, C., 1951. Notizie generali sul giacimento fossilifero di Sahabi. Storia degli Scavi - Risultati. Rendiconto delle Accademia Nazionale dei XL Roma, 1–33.] who discovered the snout and described it as being “di dimensioni più piccolo” (of much smaller dimensions) than another anthracothere skull found in the same general area at Sahabi which measured 70cm in total length. Until the holotype snout is relocated, some doubt must of course persist as to its precise status. Estimated dimensions of the teeth of the type specimen of L. petrocchii based on scaling Bonarelli''s figures to the measurements that he provided in the footnote on p. 26, indicate that it falls within the low end of the range of metric variation of Libycosaurus anisae (Black, 1972). Morphologically, L. petrocchii and L. anisae are similar, the supposed divergence between them being based on differences between the “false” type specimen from Sahabi mentioned by [Black, C., 1978. Anthracotheriidae, in: Maglio, V.J., Cooke, H.B.S. (Eds.), Evolution of African Mammals. Harvard University Press, Cambridge, pp. 423–434.] and the small specimens from Beglia, Tunisia. There are two other species of Libycosaurus in Libya, both of which are larger than L. petrocchii. The same two species occur in Chad. Libycosaurus increased in size throughout its known stratigraphic range (Faunal Sets P IV to P VII, ca. 14 to ca. 6Ma equivalent to MN 8 to MN 13) and as such it is potentially a useful biochronological indicator for deposits in which it occurs. The species L. petrocchii (and its synonym L. anisae) ranges in age from about 12 to 10Ma, the unnamed intermediate sized species ranges from ca. 10 to ca. 8Ma, and the very large species from ca. 8 to ca. 6Ma. This suggests that the Sahabi sedimentary succession spans about six million years and that the Toros–Ménalla deposits span about four million of geological time. [Copyright &y& Elsevier]