The stratigraphic distribution of the Late Callovian to Early Oxfordian dinoflagellate cyst Stephanelytron Sarjeant 1961 emend provides new evidence pertaining to its evolution. Middle and Upper Callovian times favoured the development of speciations to a short-ranging Stephanelytron community with corona(s) in ventral–posterior position (Stephanelytron brontes, S. callovianum, S. ceto and S. tabulophorum) from eurytopic species with antapical coronas (S. caytonense, S. membranoidium, S. redcliffense and S. scarburghense). The former group of species (except S. tabulophorum) may represent an example of peripatric speciation from an unfavourable mutation. The reduced stratigraphic range gives the appearance of an endemic population. The genus Lagenadinium Piel, 1985 is a junior synonym of Stephanelytron Sarjeant, 1961. A new emendation of Stephanelytron, two new combinations (S. callovianum and S. membranoidium) and two new species (?S. brontes and S. ceto) are proposed.
- Received December 16, 1998.
- Accepted April 20, 1999.
- © 1999 The Micropalaeontological Society