RETALLACK, GREGORY JOHN. Department of Geological Sciences, University of Oregon, Eugene, Oregon, 97403-1272. - Peltaspermaceous affinities of "Dicroidium" callipteroides from the earliest Triassic, basal Narrabeen Group, Australia.
The earliest Triassic, Coal Cliff Sandstone (basal Narrabeen Group) in
the roof shales to the latest Permian Bulli Coal in the Southern
Coalfield of New South Wales, Australia, contains a depauperate flora
of ferns, lycopsids, conifers and seed ferns, that survived the
greatest mass extinction of all time at the Permian-Triassic boundary.
Only one taxon of seed fern is known from this flora and its
affinities have been unclear until recent discovery of its
reproductive organs. The leaves are coriaceous, bipinnate and
bipinnatifid, and its terminal unipinnate rachides show multiple
dichotomies of the rachis. These leaves were referred to
"Thinnfeldia" callipteroides", based on type
material from the earliest Triassic, Sakamena Group of Madagascar, by
John Townrow. However, the stomatal apparatus of the leaves is
cyclocytic with papillate subsidiary cells, quite distinct from the
doubly cyclocytic non-papillate subsidiary cells of Middle to Late
Triassic Thinnfeldia, and identical to the stomatal apparatus
of Lepidopteris. Despite this cuticular similarity, Mary White
has used rachis dichotomies as a character to transfer these leaves to
"Dicroidium" callipteroides. Newly discovered ovulate
fructifications of this taxon consist of branching systems of peltate
ovular heads each with about 10 distinct marginal lobes, referrable to
the genus Peltaspermum. In a large collection of these
fructifications no more than 2 ovules were seen per head, although it
is possible that others had been abscised. Microsporophylls also were
found, and are still under investigation, but are also compatible with
peltasperm rather than corystosperm affinities. This taxon of seed
fern shows clear affinities to European peltasperms, and probably
invaded Gondwanaland from the north during earliest Triassic
postapocalyptic greenhouse of the earliest Triassic. It is also a
plausible ancestor of corystosperms such as Dicroidium, which
first appears higher within the Narrabeen Group (upper Bulgo
Sandstone) in the Southern Coalfield of New South Wales.
Key words: Australia, Dicroidium, Peltaspermum, pteridosperm, Triassic