KLAVINS, SHARON D. Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045. - Anatomically preserved gymnosperms from the Late Devonian of Ireland.
Within the last forty years, understanding of the early radiation of
the gymnosperms has been greatly augmented by the description of
numerous gymnospermous reproductive structures from the Late Devonian
and Early Carboniferous. While a great deal of data have been amassed
from anatomically preserved specimens from the Early Carboniferous,
most specimens identified from Late Devonian sediments have been based
on compression fossils. A suite of disarticulated gymnospermous
specimens has been recovered from Late Devonian (latest Famennian)
sediments from Hook Head, County Wexford, Ireland. Three different
types of ovules, a pollen organ, and vegetative axes are anatomically
preserved in pyrite and fusain. Two of the ovules have not been
previously described and the third represents a new report of
Hydrasperma Long. The two new ovules are radially symmetrical
with four integumentary lobes. Both types of ovules display
hydrasperman reproduction. The larger of the two ovules possesses an
integument composed of three distinct layers, a feature not previously
described for Devonian gymnosperms. The pollen organ is comprised of
a cluster of four microsporangia, the organization of which is
consistent with lyginopterid pteridosperms. Scanning electron
micrographs of the vegetative axes show tracheid wall thickening
patterns, which include scalariform-bordered pits, circular-bordered
pits, and crowded pitting. These new ovules increase the total number
of anatomically preserved ovules from the Devonian to five and the
total number of ovules known from the Devonian to thirteen. The known
diversity of gymnosperms in the latest Famennian suggests that future
efforts in understanding the origin of this group should focus on
Frasnian or even Givetian sediments.
Key words: anatomy, Devonian, gymnosperms, Ireland, Lyginopteridaceae, ovules