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Dinosaur-era fossil found in northern Hawke’s Bay - 12/06/2014

Paleontologists have found one of New Zealand’s largest ammonite fossils in a streambed in northern Hawke’s Bay.

Ammonites were a type of squid with a shell and were common in New Zealand coastal waters at the time of the dinosaurs. Like the dinosaurs, they were wiped out about 66 million years ago.

Ammonite fossil finds are rare in New Zealand and this one has reinvigorated the fossil-hunting community who have long held that other specimens are waiting to be found in New Zealand’s under-explored back country.

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There have been relatively few of these creatures found in New Zealand so far, so this specimen represents an important part of our geological and paleontological history

Dr James Crampton

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GNS Science paleontologist James Crampton and collections manager John Simes discovered the fossil in a 60kg boulder as they walked up a remote stream during a reconnaissance field trip in March this year.

The area is inland from Mohaka and south of Lake Waikaremoana, and borders the area where noted amateur fossil hunter Joan Wiffen first discovered evidence of land-based dinosaurs in New Zealand.

The find is remarkable for two reasons. First, it was just sitting in the riverbed waiting to be found. Second, at 90cm across, it is much bigger than other ammonites found in northern Hawke’s Bay, which are typically just a few centimetres in diameter.

The largest fossilised ammonite found in New Zealand measures 1.42m across and is on display in Te Papa. It is the third largest in the world. The biggest is from Germany and is 2.55m in diameter.

As a class of marine animal, ammonites were good swimmers and may have avoided predation by squirting ink, much like today’s cephalopods, which are their modern-day relatives. They could also sink like a stone to escape predators, or swim fast in pursuit of small prey.

The large fossilised ammonite fragment (right), compared to a smaller complete fossil which is just 165mm in diameter.   The area outlined in red on the smaller fossil indicates the section discovered in northern Hawke's Bay.

The large fossilised ammonite fragment (right), compared to a smaller complete fossil which is just 165mm in diameter. The area outlined in red on the smaller fossil indicates the section discovered in northern Hawke's Bay.

Their shells were coiled like a snail's and made up of a series of walled-off chambers that enabled them to adjust their buoyancy and swim freely in the sea.

The sandstone boulder in which the fossil was embedded was deposited on the seafloor about 85 million years ago, making it one of the youngest fossilised ammonites found in New Zealand. The fossil occupied one corner of the shell-encrusted boulder.

"There have been relatively few of these creatures found in New Zealand so far, so this specimen represents an important part of our geological and paleontological history,” Dr Crampton said.

"It may help us understand more about why ammonites were so seemingly rare here when they appear to have been so common in other places.

"Even back then, it would seem, there was something unusual about New Zealand's marine environment."

The section of the Waiau River where it was found has been visited by perhaps only three professional geologists in the past 60 years before this year’s field trip. Large parts of the river run through steep, hard-to-access land and the water is often fast-flowing.

Dr Crampton said the find demonstrated just how much more there was to be discovered in New Zealand's rich but under-explored fossil record. Large parts were tucked away in inaccessible, moss-hung and waterfall-blocked streams in remote mountainous areas.

At the time the ammonite lived, New Zealand had already broken away from the super-continent Gondwanaland in much the same way as California was being wrenched from the North American continent today by the San Andreas fault.

Curations manager John Simes with the ammonite fossil which is now part of the collection at GNS Science

Curations manager John Simes with the ammonite fossil which is now part of the collection at GNS Science. Image by Margaret Low GNS Science.

Not long afterwards, a giant asteroid hit Earth and ammonites, along with dinosaurs, became extinct.

Dr Crampton said the Waiau River bed was particularly important to paleontologists because it had carved its way through a succession of geological layers.

"Walking along the Waiau is like walking back in time. In geological terms, it takes us deeper and deeper below the earth's surface without us having to dig an inch."

It was likely that the area held a wealth of secrets that could one day unlock the answers to a wide range of questions that science still has.

"If we can wander randomly up a stream-bed and pick up a fossil of this significance, in the same way as Joan Wiffen did all those years before us, imagine what we'll unearth when we really start looking."

The fossil has been chipped away from its ‘parent’ boulder and is in storage at GNS Science.

There are no firm plans to exhibit the specimen. Its strengths lie in the fact that it is important for research rather than being a handsome display piece.

The ammonite was found on land owned by the Forest Lifeforce Restoration Trust which was set up in 2006 to provide direction and funding for the restoration of threatened species of flora and fauna in the native forests of the central North Island.

The Trust generously makes its land and resources available to scientists doing work that is consistent with its values. http://www.forestlifeforce.org.nz

Listen to an interview with James Crampton on National Radio.