Diverse and abundant insect herbivory on Miocene Nothofagaceae of the Dunedin Volcano, Otago, New Zealand

Abstract

Terrigenous sediments occurring within the mid/upper Miocene Dunedin Volcanic Group in southern New Zealand contain well-preserved leaf-beds, commonly dominated by Nothofagaceae leaf fossils. Abundant insect herbivory traces occur on Nothofagaceae leaf fossils from the Double Hill and Kaikorai Valley localities, including 28 types of external foliage feeding traces, 8 types of galling and a possible fungal trace, several not described previously. Relatively high diversity of insect herbivory traces on broad-leaved Nothofagaceae suggests a high diversity of insect herbivores. The high abundance and diversity of trace fossils in combination with evidence for plicate vernation suggests that Nothofagaceae growing on the mid/late Miocene Dunedin Volcano had shorter leaf retention times than modern New Zealand Nothofagaceae. The loss of Nothofagaceae diversity from New Zealand due to cooling climate in the late Neogene could also have meant the demise of an arthropod community adapted to living on broad-leaved Nothofagaceae. Insect damage diversity and amount at Double Hill was significantly higher than at Kaikorai Valley, as well as the occurrence of plicate vernation and leaves with stunted growth forms. This suggests that there may have been some difference in the insect diversity of the two sites, relating to local palaeoenvironment, such as higher temperatures at Double Hill during the warm season and/or differences in forest density.