Evidence of profuse bark shedding in Dicroidium seed ferns (Umkomasiales) from the Triassic of Antarctica

Abstract

During the 11th German Antarctic North Victoria Land Expedition in 2015/16, exceptionally well-preserved permineralized Kykloxylon stems—the wood of the iconic Dicroidium plants of the Gondwanan Triassic—were collected from the Middle to Upper Triassic Helliwell Formation in north Victoria Land, Transantarctic Mountains, Antarctica. Some of these logs show large borings and cavities that are partly filled with multi-layered periderm. This periderm is identical in cell shape and dimensions to isolated flakes of tissue that are superabundant in bulk macerations of Dicroidium-bearing rock samples from different coeval locations in the Transantarctic Mountains. These flakes are interpreted as shed bark fragments of Dicroidium-bearing umkomasialean trees. Various hypotheses on the adaptive advantages of bark shedding are discussed, including the reduction of epiphyte load. Palynological data document an abundance of potentially epiphytic cryptogams (spikemosses and bryophytes) in the environments in which the Dicroidium trees grew, and modern ecosystems with a climate comparable to that of the Late Triassic in Antarctica are in many cases also characterized by a lush epiphyte vegetation. Another advantage could lie in the reduction of infections by phytopathogenic microorganisms, as abundant fungal remains in both the wound periderm and the dispersed periderm flakes indicate.

Keywords

• epiphytes
• fossil wood
• palaeoecology
• periderm
• transantarctic mountains
• gondwana