Ellen Cieraad's Research

Quantative plant ecology & physiology


Leave a comment

Fossil ferns

Pikopiko Fossil Forest near Tuatapere in Southland may not be as well-known as the Curio Bay petrified forest but it has one of the richest known Cenozoic* fern floras globally. Walking in between the in situ fossil tree stumps (probably related to Araucaria) on the shores of the Wairau River, you get a sense of the spacing of the trees. Underneath your feet, the fossil litter layers provide insights into this ancient forest community. The diversity and abundance of ferns implies that ferns dominated the evergreen, tall forest understorey just as they do in modern New Zealand rainforests. Eight fern macrofossil groups (parataxa) and 20 very tiny spore types have been identified from the fossil forest. The ancient flora encompasses at least 40% of modern New Zealand fern families, which highlights the long history for some fern genera in the region. The abundance of ferns, the presence of fungi on many leaves and the presence of palms is evidence for warm humid conditions in Late Eocene New Zealand.

Pikopiko-fossil-forest_imagelarge_GNS

Pikopiko fossil forest

Colleagues of mine recently re-examined fossil fern material I used for my MSc thesis together with more fern macrofossils from these Eocene strata (c. 35 million years ago), the first records for New Zealand. The results are published here.

Homes AM, Cieraad E, Lee DE, Lindqvist JK, Raine JI, Kennedy EM, Conran JG 2015. A diverse fern flora including macrofossils with in situ spores from the Late Eocene of southern New Zealand. Review of Paleobotany and Palynology 220: 16-28. doi:10.1016/j.revpalbo.2015.04.007

The discovery of three types of fossil fern fronds bearing sporangia with in situ spores enabled us to roughly identify the ancient ferns and show for the first time that some relate to a present day fern genus (including Blechnum, and Thelypteris subgenus Cyclosorus), some to an extinct group of uncertain affinity and some to a widely known fossil spore form taxon. Five additional fern groups, including another probable Blechnum, could be distinguished on the basis of sterile foliage.

The fern flora recovered from Pikopiko Fossil Forest is significant in being the first record of fern macrofossils from Eocene strata (56 to 33.9 million years ago) in New Zealand, and they provide a wider understanding of the natural history of New Zealand during this time.

*The Cenozoic period is from 65 million years ago to the present day.

Photo credit: GNS