A diverse fern flora including macrofossils with in situ spores from the Late Eocene of southern New Zealand

Abstract

Three types of fossil fern fronds bearing sporangia with in situ spores are described from the late Eocene Pikopiko Fossil Forest, southern New Zealand. They are referable to the extant fern genus Thelypteris subgenus Cyclosorus (Thelypteridaceae) and an extinct fern of uncertain affinity. The matching of Thelypteris (Cyclosorus) macrofossils to the spore form taxon Laevigatosporites ovatus is recognised for the first time. Five additional fern taxa, including another probable Blechnum, are distinguished on the basis of sterile foliage. The Pikopiko site is one of the richest known Cenozoic fern floras globally and the diversity and abundance of ferns (eight fern macrofossil parataxa and 20 miospore types) implies that ferns dominated the evergreen, tall forest understorey as in modern New Zealand rainforests. At least 40% of modern New Zealand fern families are represented in this 35 Ma flora and the discovery of fronds with in situ spores of a type recorded throughout the Cenozoic in New Zealand supports a long history for some fern genera in the region. The abundance of ferns, epiphyllous fungi on many leaves and the presence of palms is evidence for warm humid conditions in Late Eocene New Zealand. Keywords New Zealand; Fossil ferns; Blechnum; Thelypteris; Pikopiko fossil forest; Late Eocene