Macrofossils associated with the fossil fern spore Cyatheacidites annulatus and their significance for Southern Hemisphere biogeography

Abstract

Oligocene-Early Miocene macrofossils of parts of a fertile frond are assigned to the extant South American species Lophosoria quadripinnata (Gmel.)C.Chr. These macrofossils bear the dispersed spore species Cyatheacidites annulatus Cookson ex Potonie. This species has an extensive recorded history in the Southern Hemisphere, only recently retracting to its current range. This history suggests major episodes of expansion and extinction, with a double extinction occurring in Australia and Cenozoic introductions to the Kerguelen Islands and the Falkland Plateau that probably involved transoceanic dispersal. Cretaceous Lophosoria records may or may not include L. quadripinnata, but they probably included several species, especially in the southern South America-Antarctic Peninsula region, where other dispersed spore species of Cyatheacidites and the macrofossil species L. cupulatus are recognised. This species diversity probably collapsed during the Cretaceous, possibly due to angiosperm radiation. The Cenozoic record of C. annulatus in Australia appears to represent a radiation of L. quadripinnata, probably from South America.