Museum Notebook: Fossils and other interesting finds along Whanganui coastline

Dark grey fossil oyster shells like this one are common on local beaches. Huge numbers of them have fossilised here over the last five million years. Photo / Whanganui Regional Museum

Over recent weeks, I have worked with hundreds of school children along the Whanganui coastline helping them to discover what lives there.

Given a challenge to look for interesting items, the children found numerous triangle shells (Spisula aeqilateralis), many with the live mollusc still inside, holding their dual shells tightly closed.

A tasty treat for seabirds as well as humans.

They found many other shells too, including fossils.

Whanganui beaches are littered with fossil shells of different kinds, especially oysters.

The fossils prompted fascinated responses from children of all ages and amazement at finding something that lived millions of years ago.

Some have washed out of the soft papa cliffs, are less than a million years old and can still be found on our beaches today.

Others have eroded from harder, older rock.

These local fossils are, in geological terms, still very young, being only up five million years old.

They are a reminder that the entire Whanganui region lay under the ocean until relatively recently.

From a high vantage point, such as the Durie Hill Tower, the Whanganui landscape includes a series of flat-topped hills.

These are old seabeds, stranded by the gradual uplift of this region at the rate of a miniscule 0.3mm per year.

Over a period of one million years, that amounts to 300 metres of elevation. Locked up in those uplifted marine terraces are the climatic and biological record of the marine environment at the time.

The gigantic tooth of an extinct megalodon shark (Carcharocles megalodon). Photo /Whanganui Regional Museum Collection ref: 1800.175

Oysters from long vanished reefs, cockles form ancient mudflats, scallops from sandy seabeds and many more species.

They are all part of what geologists call the Whanganui series. Whanganui rocks and the fossils preserved in them are regarded worldwide as one of the most complete records of the last five million years of climate change.

In the museum's exhibition Hāhā te Whenua-Young Land, examples of typical Whanganui series fossils can be seen, including many that can readily be found washed up along the local beaches.

Other more surprising and unusual finds, like the gigantic tooth of an extinct megalodon shark (Carcharocles megalodon), were exposed along river cliffs or by road cuttings and quarries. You never know what interesting fossils you will find once you start looking.

Anyone keen to find out more about the fascinating topic of Whanganui geology is warmly invited to join us in the Davis Theatre, Watt St, on Friday, April 9 at 7.30pm.

Museum Notebook

Dr Hamish Campbell, one of New Zealand's leading palaeontologists and geologists, will explain the special role that the Whanganui region has in the geological record of Zealandia, our mostly submerged continental home.

Dr Campbell, who has recently retired from the role of science communicator at GNS Science, was also the geologist at Te Papa for over 20 years.

The talk will be followed by a Saturday morning field trip on April 10 to Durie Hill and Ototoka Beach, leaving from the museum carpark at 8.30am. For more details and to book your space on the field trip, phone the museum on 06 349 1110.

•Margie Beautrais is the educator at Whanganui Regional Museum.