Strother, Paul K , Taylor, Wilson A. .
Cryptospore Evolution during the Lower Paleozoic.
Although there is debate about the definition of the palynological group, cryptospore, it is becomming increasingly evident that these spore-like microfossils have a stratigraphic distribution that begins in the Middle Cambrian and extends to the Cambro-Ordovician boundary. Steemans has suggested restricting the cryptospores to alete miospores derived from embryophytes. Based on this restricted view, tetrahedral tetrads that originate in the Middle Ordovician (Llanvirnian) and become common during the Caradoc, would represent the basal embryophytes. However tetrahedral tetrads are not a prequisite for embryophyte affinity - many bryophyte spores today are small nondescript and irregular in form.
A more liberal view is that cryptospores could be the remains of any number of pre-embryophytic groups that had adapted to aquatic and subaerial habitats. Beginning in the Middle Cambrian Rome Fm (Tennessee, US), polyads, irregular tetrads, dyads and solitary sporomorphs become common elements of estuarine to paralic palynomorph assemblages. TEM analysis of dyads shows wall ultrastructure more similar to the liverworts than any other group. Either embryophytes were present during the Middle Cambrian, or embryophytic spore characters were evolving prior to the origin of the Embryophyta. The stratigraphic distribution of cryptospores cannot make this distinction, but the turnover of cryptospore to trilete spore dominance in the Homerian (middle Silurian) is coincident with the first record of plant mesofossils with tracheids.
1 - Boston College, Geology & Geophysics, Weston Observatory, 381 Concord Road, Weston, Massachusetts, 02493-1340, USA
2 - University Wisconsin at Eau Claire, Biology, Eau Claire, Wisconsin, 54701, US
Presentation Type: Paper
Location: Maybird (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 8:30 AM