Yulebacaulis normanii gen. et sp. nov., a new fossil tree fern from south-eastern Queensland, Australia

Abstract

Although possibly reworked, a silicified specimen consisting of outer cortex, petioles, aphlebiae and roots was collected from the Lower Cretaceous Mooga Sandstone or Tertiary sediments which lie topographically above the site near Yuleba, Queensland, and represents the new genus and species Yulebacaulis normanii. The petioles in this specimen lack stipular wings and epidermal trichomes or scales. Its clepsydroid-shaped petiolar vascular strands are oblong, straight and elongated tangential to the missing stele. Clusters of parenchyma cells at the ends of the strands form 'peripheral loops' and, at higher levels of the petioles, the 'loops' open, freeing C-shaped aphlebiae traces. Non-filiforrn aphlebiae produced by the petioles are numerous. Yulebacaulis normanii is anatomically similar to Asterochlaenopsis kirgisica (Stenzel) Sahni from the Permian of western Siberia. They differ by the peripheral loops in Y. normanii remaining open after the C-shaped traces depart, rather than staying closed as in A. kirgisica. The trace also begins as a loop in A. kirgisica and not in Y. normanii. Aphlebiae fork repeatedly in the former species and only twice in the latter. Faecal pellets produced by some small animals are present between the petioles, in the aphlebiae, and in borings in the inner and outer cortices of some petioles of Y. normanii. Based upon the size ranges of the faecal pellets, three different animals may have been involved. The pellets are loosely packed, almost filling the galleries, and appear to have been deposited by the animals as they fed upon the cortical cells. The anatomical features of Yulebacaulis are very close to some members of the Zygopteridales. If it is Early Cretaceous in age, then by assigning this genus to this group the age of this order would be extended from Upper Palaeozoic into the mid-Mesozoic.