Biodiverse Middle Eocene Molluscan Fauna From Kaeo, Northland, New Zealand

A recently discovered fossil locality in glauconitic Ruatangata Sandstone near Kaeo, Northland, New Zealand, contains the most species‐rich Eocene (middle Eocene, Bortonian Stage) molluscan fauna in the North Island. Most shells have dissolved away leaving a rich collection of molds and casts of 60 molluscan taxa (31 bivalves, 29 gastropods). Twenty‐nine are confidently and 11 tentatively identified to species level, 17 to genus and 3 to family level. A new species of mussel, Botula kaeoensis Eagle n. sp., is described. It is the only New Zealand record of this subtropical genus. Also present is the earliest New Zealand fossil record of the limpet genus Cellana. The record of Costacallista hectori extends its time range up into the late middle Eocene (Bortonian). The autecology of each species is summarised and shows that a wide range of sessile and mobile trophic types are represented. Analysis of the depth ranges of their extant relatives shows that the fauna is a mixture of sublittoral, inner shelf, mid shelf–upper bathyal taxa that lived on a variety of hard and soft shore substrates. All bivalves are disarticulated single valves, and we infer the Kaeo fauna was brought together at mid–outer shelf depths by storm waves and bottom currents.