Abstract Detail

Paleobotany

Nibbelink, Megan [1], Atkinson, Brian [2], Mindell, Randal [3], Matsunaga, Kelly [4].

A new permineralized cyathealean fertile frond segment from the Late Cretaceous of British Columbia, Canada.

The Cyatheales, or tree ferns, have a complex taxonomic history but are presently composed of 713 species organized in 13 genera and eight families. Today, the Cyatheales are found in tropical to temperate regions around the world and include species with both arborescent and creeping growth forms. Fossils assigned to Cyatheales are common components of Mesozoic floras worldwide from the Early Jurassic through Early Cretaceous. Despite a rich fossil record, anatomically preserved fertile material is scarce. A new specimen of a permineralized fertile frond segment from British Columbia contributes new data to the fossil record of Cyatheales. It is preserved in a calcium carbonate concretion collected from Trent River Formation (Santonian, 86.3–83.6 Ma) deposits exposed along Oyster River in Vancouver Island, British Columbia. The fossil was prepared using the cellulose acetate peel technique. The specimen consists of six ultimate segments, two of which are complete, pinnately arranged along a leaf axis. The total number of branching orders is unknown. The frond segment is about 56 mm long, bears sixteen sori, most of which are mature, and has a slightly reduced lamina. Ultimate segments have 4-5 sori, approximately 400 –750 µm wide, supplied individually by a vascular bundle. Sori are marginal with bivalvate indusia. Sporangia are attached to a slightly raised receptacle by a multiseriate stalk composed of 4 cell columns and exhibit gradate maturation within the sorus. Annuli are oblique. In situ spores are psilate, approximately 25 µm wide. The aperture is trilete with a margo and deep depressions between the arms. This suite of reproductive characters is found today in the genera Culcita (Culcitaceae) and Dicksonia (Dicksoniaceae). These genera were historically part of Dicksoniaceae but are now assigned to their own families, which are distantly related within Cyatheales. While neither genus has completely smooth spores, some species in both genera have a smooth exospore upon which the perispore is laid down, resulting in various ornamentation patterns. This perispore deposition occurs in the latest stages of spore maturation, and thus its absence in this fossil could be developmental. Tomographic reconstruction of the fossil is currently underway, which will hopefully reveal characters that will allow us to assign the fossil to Culcitaceae, Dicksoniaceae, or an extinct taxon. This work highlights some of the challenges of understanding relationships among living and fossil leptosporangiate ferns in light of current phylogenies, which have broken up many morphology-based classifications and demonstrated convergent evolution of reproductive traits within and between major clades.

1 - University Of Kansas, 1200 Sunnyside Avenue, Lawrence, KS, 66045, United States
2 - University Of Kansas, Ecology And Evolutionary Biology, 1246 West Campus Road, LAWRENCE, KS, 66044, United States
3 - Botany, #3529 - 6270 University Boulevard, University Of Alberta, Vancouver, BC, V6T 1Z4, Canada
4 - University Of Kansas, Ecology And Evolutionary Biology, 1200 Sunnysive Ave., Lawrence, KS, 66045, United States

Keywords:
fern
sorus
Cyatheales
Dicksonia
Culcita
fossil
Cretaceous.

Presentation Type: Oral Paper
Number: PB2006
Abstract ID:743
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award