61 An encrusting coral on an oyster shell from Chatton

The holotype of an unusual species of encrusting coral is held in the Geology Museum type room. It is part of an extensive collection of fossils from southern New Zealand made by Harold Finlay during his time at the University of Otago in the 1920s. Most of his collection of fossil and living molluscs is now held by the Auckland Museum, but a few corals and other invertebrates remain in the Geology Department at the University of Otago.

This specimen, named Rhizangia aotearoa by DF Squires in 1958 consists of eight complete and three fragmentary corallites forming a spreading mat on the shell of a fossil oyster (Ostrea sp.). Each of the small corallites, 3 to 5 mm in diameter, would have housed a tiny coral polyp during life. Together they form a small colony with the individual corallites forming the entire coral skeleton. The tiny corallites have simple septa, unlike most other related stony corals.

Known only from the Chatton Formation at its type locality near Gore, in Southland, this is the only record of this genus in New Zealand. All other species in this fossil genus are from European fossil localities that range in age from Cretaceous to Eocene. However, in a recent revision of rhizangiid corals by European researchers, no mention is made of the New Zealand fossils. Further research is evidently needed to confirm the identity of this interesting little coral.

— Written by Daphne E Lee and Jeffrey H Robinson