An international team of scientists has discovered a fossil found in a Canterbury stream four decades ago is 246 million years old.
That makes the nothosaur the oldest ancient polar sea reptile found in the Southern Hemisphere.
"A nothosaur is a long reptile with a long neck, a long tail and it's got paddles - flippers. And it's got a rather small head flattened with teeth out the sides," said Hamish Campbell, a palaeontologist with GNS.
It would have eaten fish or squid and may have grown up to 7m long.
That kind of key information is held within one of its fossil vertebrae.
"It was a small boulder and I spotted it with my father in 1978, I was only 25. I could see it was a complete, whole bone," Campbell told Newshub.
The nothosaur predates the previously oldest-known Southern Hemisphere aquatic reptile by more than 40 million years.
It lived in a shallow coastal environment teeming with a rich community of marine creatures.
"This group of organisms - marine reptiles - were around for 180 million years and this specimen is one of the earliest known at 246 million," said Campbell.
It's a rich record of Triassic time held within greywacke rocks that form much of the Southern Alps.
But it's not the first globally significant fossil discovered in Canterbury.
Giant penguins once roamed the area at a time when the world was experiencing extreme global warming.
"The reason why Canterbury has such a rich fossil record is because of the abundance of marine sedimentary rock formation," Campbell said.
Which means it's likely there are many more ancient mysteries waiting to be uncovered.
