Dordrechtites arcanus, an anatomically preserved gymnospermous reproductive structure from the Middle Triassic of Antarctica.

摘要

The genus Dordrechtites is an isolated ovulate structure previously described only from South Africa and Australia as impressions. The discovery of compressed and permineralized specimens of this taxon at the base of Mt. Falla (uppermost Fremouw Formation) in the central Transantarctic Mountains extends the geographical and geological distribution of the genus and increases the known floral diversity of the Triassic of Antarctica. The first permineralized species is described, D. arcanus, which includes internal anatomy of the two elongate arms and central cupule containing two elongate, bilaterally symmetrical, orthotropous ovules. An arc-shaped collateral vascular bundle extends from the arm into the top of the cupule, branches and then extends around the ovule to about halfway down to the micropylar end. The cupule is parenchymatous and includes transfusion tissue with cells that have pitted walls. The sclerotesta of the ovule is up to 200 µm thick, consisting of an outer layer with longitudinally oriented, thick-walled cells, and an inner layer one cell thick, of rectangular, thick-walled cells. The micropyle is flared at the attenuated tip of the pyramidal cupule. The four previously described species of Dordrechtites have uncertain affinities and further the new species described herein is considered incertae sedis within the gymnosperms.