Resolving the green branch of life: Current progress and future challenges
Schuettpelz, Eric , Schneider, Harald , Pryer, Kathleen M. .
An evolutionary time-scale for ferns: ancient origins and recent radiations.
Ferns, like their sister group—seed plants, have a long evolutionary history. Unequivocal fossil representatives from both lineages were present in the Devonian. From the subsequent fossil record, three successive leptosporangiate fern radiations have been proposed: (1) a Carboniferous radiation yielding several now-extinct families of uncertain position; (2) a radiation beginning in the Permian and culminating in the Jurassic that saw the establishment of the extant early-diverging leptosporangiate lineages, and perhaps also the more derived, polypod fern lineage; and (3) a Cretaceous or later radiation of polypods. However, as a result of an incomplete fossil record, a full understanding of the trends in fern evolution and diversification is not possible using paleobotanical evidence alone. Here we take a more comprehensive approach, integrating molecular phylogenetic data with fossil constraints. Our results are largely in accord with previous ideas, but suggest that earlier hypotheses may have been overly simplified. We show that by the end of the Carboniferous, all five extant fern lineages—ophioglossoids, whisk ferns, marattioids, horsetails, and leptosporangiates—were present, and the earliest divergence within crown-group leptosporangiate ferns (giving rise to the osmundaceous ferns) had also occurred. The Permian witnessed the establishment of four additional leptosporangiate lineages—gleichenioids, filmy ferns, schizaeoids, and the core leptosporangiates. A subsequent Triassic diversification of the core leptosporangiates gave rise to the heterosporous ferns, tree ferns, and polypods. Despite the ancient origins of all the major extant fern lineages, the bulk of the diversification within these lineages is more recent; several successive radiations in the Cretaceous generated most of modern fern diversity. Although much of the diversification occurred within polypods, which now account for more than 80% of ferns, the Cretaceous radiations were not confined to this group. Concurrent diversifications in several other fern lineages raise important questions about the evolutionary processes underlying fern diversity.
1 - University of Goettingen, Department of Systematic Botany, Albrecht von Haller Institute for Plant Sciences, Untere Karspuele 2, Goettingen, D-37073, Germany
2 - Duke University, Department of Biology, 139 Biological Sciences Building, PO Box 90338, Durham, North Carolina, 27708-0338, USA
divergence time estimates
Presentation Type: Symposium
Location: Ballroom 3 (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 11:15 AM