One of New Zealand’s largest ammonite fossils has been discovered in a Hawke’s Bay streambed. The squid-like creature, which lived in the sea during the time of the dinosaurs, had a flat spiral shell that looked something like a Paper Nautilus but was between 80 and 90 cm in diameter, large compared to most other ammonites.
GNS palaeontologist Dr James Crampton and collections manager John Simes were surprised by the important find, made recently during an informal ‘rock kicking’ walk up the Waiau River bordering the Maungataniwha Native Forest in inland Hawke’s Bay.
Although found relatively frequently elsewhere, ammonite fossils are rare in New Zealand for reasons not yet completely understood.
“We don’t have a significant record of these creatures in New Zealand so this find adds considerably to what we know about NZ paleontological history and about what was living here at that time,” 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 find demonstrates just how much more there is to be discovered in New Zealand’s rich but under-explored fossil record. Large parts of that record are tucked away in inaccessible, moss-hung and waterfall-blocked streams in our remote mountains.
Maungataniwha is owned by the Forest Lifeforce Restoration Trust which provides direction and funding for the restoration of threatened species of fauna and flora in native forests. Mangahouanga Stream, where celebrated New Zealand palaeontologist Joan Wiffen first discovered evidence of land-dinosaur fossils in New Zealand, has the bulk of its catchment here.
Ammonites belong to a group of predators known as cephalopods. Their living relatives include octopus, squid, cuttlefish and nautilus. Its shell was coiled like a snail’s and comprised a series of water-tight compartments that enabled it to float and swim in the upper layers of the sea.
The largest fossilised specimen discovered in New Zealand measures 1.42 metres across and is now on display in Te Papa. It is the third largest discovered anywhere. The biggest is from northern Germany and is 2.55 metres in diameter.
Most ammonite fossils found in this part of New Zealand are only a few centimetres in diameter so the Waiau River find is significant. It was found in strata created 85 million years ago, making it one of the youngest fossilised ammonites found here.
At that time New Zealand had already been torn away from the super-continent Gondwanaland in much the same way as California is being wrenched from the North American continent today by the San Andreas fault. Not long afterwards a giant asteroid hit Earth and ammonites, along with dinosaurs, became extinct.
Crampton said the Waiau River bed was particularly important to palaeontologists because it had carved its way through a succession of geological layers.
“Walking along the Waiau is like walking back in time,” he said. “In geological terms it takes us deeper and deeper below the earth’s surface without us having to dig an inch.”
He said it was likely that the area held a wealth of secrets that could one day unlock the answers to a wide array 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 GNS team will attempt to remove the entire fossil from the 50kg boulder it was contained within, with the aim of displaying it at its offices in Lower Hutt.