Reassessment of Palaeothamnium Conti, 1946 (Corallinales, Rhodophyta)

Palaeothamnium has been identified in many algal associations from the Late Cretaceous to the Miocene since its definition by Conti (1946b). Revision of Conti's original collection and of new material from the type localities in the Vienna Basin indicate that the developmental stages of the conceptacles of the type species P. archaeotypum are common in many other present-day and fossil coralline algae belonging to different genera of the subfamily Melobesioideae and therefore cannot be considered a diagnostic generic character. The presence of flat epithallial cells and long subepithallial initials together with a well-developed peripheral region in the type species leads us to consider Palaeothamnium as a younger heterotypic synonym of Lithothamnion Heydrich, 1897. However, according to modern melobesioid taxonomy, its attribution to Synarthrophyton Townsend, 1979 cannot be completely excluded. In addition, the type species of Palaeothamnium must be treated as a younger heterotypic synonym of Lithothamnion ramosissimum (Reuss, 1847) Piller, 1994.