IN THE IDENTIFICATION OF FOSSIL CORALLINE ALGAE
by Michael Rasser
Until recently, several diagnostic characters used in present-day coralline red algal taxonomy where thought to be unpreservable in fossil material. Wray (1977) and Poignant (1984) therefore concluded that fossil and Recent coralline algae have to be classified in different ways. The taxonomy of fossil coralline algae has usually focused on calcified characters with a high fossilisation potential such as the arrangement of basal filaments, the perforation of asexual conceptacles, and the occurrence of trichocytes (Wray, 1977). The taxonomy of Recent coralline algae, however, uses additional characters including cell-connections, the shape of epithallial cells, the length of subepithallial initials, and the formation of sexual reproductive organs (Woelkerling, 1988; Braga et al., 1993). Consequently, some genera and most species described from fossil material cannot be compared to any Recent taxon. This would, however, be crucial for the understanding of coralline algal phylogeny, palaeoecology and palaeobiogeography.
Braga et al. (1993) demonstrated, using the genus Spongites Kützing (1841) as an example, that key features of present-day taxonomy such as cell-connections, epithallial cells, and subepithallial initials are indeed preservable and can occasionally be recognised in fossil coralline algae. Since then, several studies have dealt with the identification of fossil taxa using diagnostic characters used in present-day taxonomy (Bassi, 1995a; 1995b; Braga & Aguirre, 1995; Aguirre et al., 1996; Basso et al., 1996; 1997). Braga et al. (1993) additionally presented an identification key for fossil coralline algae which is a basic approach to the unification of fossil and present-day taxonomy. This key nevertheless shows that traditional characters still have to be regarded in the identification of several fossil genera. This is due to the fact that several key features used in Recent taxonomy, such as the formation of sexual reproductive organs, have not yet been observed in fossil material.