DOWER, BEATRICE L.* AND RICHARD M. BATEMAN. Department of Geology, University of Pennsylvania, 240 South 33rd Street, Philadelphia, PA19104-6316., Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, U.K. - Morphological and anatomical investigations of exceptionally preserved cycadophyte leaves from the Jurassic of Skye, NW Scotland.
The Middle Jurassic (AalenianBajocian) marine beds of Bearreraig,
Skye, NW Scotland, have yielded extremely well-preserved leaves of
cycadophytes. In this study the anatomy and morphology of three leaf
fragments were examined for taxonomic purposes, and to determine
whether the anatomical features might shed light on the environment
and phylogenetic relationships. The specimens were preserved as
calcite permineralizations in nodules that formed in near shore marine
deposits. The specimens revealed details of anatomy greatly exceeding
published descriptions of similar species, comparable arrangements of
vascular tissues in the rachis have been described only from the
fossil Ptilophyllum cutchense Morris (Cycadales) from
India. Based on morphological rather than anatomical characters, one
leaf has been tentatively identified as Nilssonia cf.
tenuinervis Seward (Cycadales) and the other two leaves as cf.
Otozamites penna Morris (Bennettitales). Permineralized
cycadophyte floras are found in only four other localities worldwide,
but the most relevant to the Skye flora is that of the Jurassic
(AalenianBajocian) of Yorkshire, in which plants are preserved as
adpressions. Consequently, past studies of the Yorkshire Flora have
emphasized exclusively the morphological aspects of the taxa
recovered. Given the exquisite anatomical preservation of the Skye
flora, significant data on anatomical and structural adaptations seen
in these plants and their environments may be forthcoming. According
to most recent phylogenetic analyses, the Cycadales and the
Bennettitales are distantly related. On comparison with living cycads,
the anatomy of the Nilssonia leaves shows certain similarity to
midribs of Stangeria Moore. The bennettite Otozamites
shows similarity to the petioles of Bowenia Hooker, and appears
to contradict the accepted phylogenetic positions. However, leaf
characters have been underused in phylogenetic analyses because
anatomical and morphological character states can be convergent in
taxa of different groups.
Key words: anatomy, Bearreraig, cycadophytes, Jurassic, Nilssonia, Otozamites