South polar greenhouse insects (Arthropoda: Insecta: Coleoptera) from the mid-Cretaceous Tupuangi Formation, Chatham Islands, eastern Zealandia

Rare insect body fossils have been discovered for the first time after 175 years of research on the Chatham Islands, eastern ‘Zealandia’. The coleopteran (beetle) insects, dated to ca 95 Ma and extracted from fine-grained, upper delta plain facies in the lower Upper Cretaceous (Cenomanian–lowermost Turonian) Tupuangi Formation at Waihere Bay on the remote Pitt Island, represent the most southern, polar-latitude (ca 70–80°S) faunal assemblage from the Cretaceous recorded to date. Three species are represented in the insect fauna: a portion of a segmented abdomen of a probable carabid? ground beetle and two distinct coleopteran elytra, one preserved with a brilliantly iridescent carapace upon discovery, comparable with Cretaceous taxa within the Buprestidae (metallic wood borers), but identification with the Chrysomelidae (leaf beetles) or Tenebrionidae (darkling beetles) can not be discounted entirely. Another specimen has more weakly preserved greenish iridescence and has a morphology consistent with Carabidae; given the preservational deficiencies and rarity of material, the specimens are attributed to Buprestidae? genus et species indeterminate and Carabidae? genus et species indeterminate A and B, respectively. These coleopteran fossils represent the only recorded iridescence in Mesozoic invertebrates from Zealandia. Importantly, these mid-Cretaceous insects existed in South Polar forests near the height of the ‘hothouse’ phase of relatively warm, alternating intervals of full daylight in the summer months and total darkness during the winter, before eastern Zealandia diverged at ca 83 Ma from the Marie Byrd Land region of West Antarctica, as part of the final break-up of Gondwana.