Morphology and ecology of the Antarcticycas plant

Abstract

The Antarcticycas plant is reconstructed from the co-occurring vegetative organ taxa Antarcticycas schopfii and Yelchophyllum omegapetiolaris and the pollen cone taxon Delemaya spinulosa from permineralized peat of the Fremouw Formation, early Middle Triassic of Antarctica. The association of the organs in the same deposit, assignment of each taxon to Cycadales, and histological features shared among the taxa suggest they were all produced by the same plant. The Antarcticycas plant is reconstructed as a small plant, possibly with a subterranean stem; it was probably similar in habit to small-stemmed species of extant Zamia. Antarcticycas stems are inferred to exhibit apical rather than axillary branching based on reinterpretation of type material that shows a branching axis accompanied by anatomy indicative of the presence of cone domes when observed in extant cycads. The presence of a bulbil on one specimen indicates that branching also took place through adventitious budding. The Antarcticycas plant is similar in its anatomy to extant cycads, although contractile tissue and coralloid roots have yet to be identified and may not have been present in the fossil plant. The plant inhabited a warm temperate polar habitat with protracted periods of winter darkness for which there is no modern equivalent. Evidence for deciduousness in this taxon, previously suggested as a possible adaptation to its warm, light-limited environment, is equivocal. The possibilities that fire played a role in the Fremouw peat ecosystem and that the Antarcticycas plant may have been insect pollinated are explored.