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) forming
roof shales to the latest Permian Bulli Coal in the Southern Coalfield of
New South Wales, Australia, contains a low-diversity 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 by John Townrow to "Thinnfeldia" callipteroides", based on
type material from the Early Triassic, Sakamena Group of Madagascar.
However, the stomatal apparatus of the leaves is cyclocytic with papillate
subsidiary cells, 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 other ovules 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
affinities with European and Russian Permian peltasperms, and probably
invaded Gondwanaland from the north during earliest Triassic
postapocalyptic greenhouse. Peltasperms are plausible ancestors 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