Abstract Detail

Paleobotanical Section

ROTHWELL , GAR W [1], Stockey, Ruth [2], Millay, Michael A. [3].

Evolution of modern Marattiales; superficially Christensenia-like synangia in the Early Cretaceous.

Marattialean ferns have an impressive fossil record that documents extensive species richness in Pennsylvanian and Early Permian floras of the Euramerican paleotropics, and which extends across the Southern Hemisphere Gondwana continent during the Permian and Triassic.  Crown group genera are widely recognized in Jurassic floras, but there is a dramatic decline in the occurrence and diversity of fossils during the Cretaceous, and a virtual absence of marattialeans from post-Mesozoic strata.  Marattialean fossils recently have been recognized within an exceptionally diverse pre-angiospermous flora from the Early Cretaceous of British Columbia, Canada.  Fossils include both polyarch roots and round to oval synangia with well-preserved internal anatomy and spores.  Synangia are radial to oval, sessile, vascularized, and are attached above veins.  Each consists of a ring of 9-13 sporangia surrounding a parenchymatous central region basally and forming a shallow cup apically.  Sporangia dehisce via a short vertical slit on the inward facing wall, and separate distally to form diminutive free tips.  The exterior synangial wall is several cell layers thick with a wrinkled outer surface.  No trichomes or other idioblasts are present.  Inner facing walls are uniseriate distally, lack labia, and the sporangial tips are not thickened.  Spores are monolete and ellipsoidal, with spinulose exine and thin granulose perispore.  Although superficially similar to extant Christensenia in synangial symmetry, slit-like dehiscence, and spore features, these synangia display a novel combination of characters not found in either a living or extinct marattialean genus.  Among the most well known Paleozoic taxa these synangia are most reminiscent of the “Cyathotrachus”-type species of Scolecopteris Zenker, particularly S. altissimus (Mamay) Millay, with which they share radial symmetry, basal vascularization, a parenchymatous central region basally, longitudinal dehiscence on interior facing sporangial walls, free sporangial tips, and monolete spores with spinulose sculpturing.  However, the Cretaceous synangia differ by being sessile, having much shorter free sporangial tips, and a larger number of sporangia/synangium than S. altissimus.  This combination characters suggests that evolution of stem group Marattiales was ongoing as late as the Early Cretaceous and that at least some crown group genera may be more closely related to Paleozoic forms than is currently thought.

1 - Ohio University, Department of Environmental and Plant Biology, Athens, OH, 45701, USA
2 - Oregon State University, Department of Botany and Plant Pathology, Corvallis, OR, 97331, USA
3 - Ohio University, Arts and Sciences - Southern Campus, Vern G. Riffe Center 157 , Ironton, OH, 45638 , USA

Keywords:
Early Cretaceous
Fossil
fern
Marattiales
synangia.

Presentation Type: Oral Paper:Papers for Sections
Session: 21
Location: Whitewater/Grove
Date: Tuesday, July 29th, 2014
Time: 8:30 AM
Number: 21001
Abstract ID:283
Candidate for Awards:None