By RNZ

Dinosaur dolphins have been found to have survived in Aotearoa’s waters long after they went extinct elsewhere.

Ichthyosaurs are marine reptiles that looked like dolphins, which died out around 100 million years ago.

A fossil was found in North Canterbury near Coverham at the northern end of Clarence River Valley in 2010 and Canterbury Museum senior curator natural history Dr Paul Scofield and University of Canterbury master’s graduate George Young spent three years studying the 4m-long fossil.

The researchers used medical scanners to penetrate concrete-hard rocks and create three-dimensional images of the fossilised bones hidden inside.

The analysis revealed the ichthyosaur was evolving from a reptile into something more like a whale and managed to survive for five million years after its peers around the world went extinct.

“It had lost its pelvis and become more like a whale or a dolphin. This specimen represents the last gasp of evolution for the ichthyosaur. Ultimately, their prolonged presence in Aotearoa may allow us to solve the riddle of why they became extinct around the world,” Scofield said.

Scofield said the most likely reason it survived longer was because of how isolated the country is.

“The most likely reason is the same reason that some of the very strange animals that occur in New Zealand today are still here, like for example a tuatara,” he said.

The site where the fossil was found in Coverham at the northern end of Clarence River Valley in North Canterbury in February 2023. Photo / Canterbury Museum

“That’s because we’re somewhat isolated, isolated from the rest of the world, and that isolation causes relictual population, so populations which aren’t subject to the same stresses and influences as animals in Europe and other places, and so that means that animals might survive a little bit longer.”

Scofield said it was still not known why ichthyosaurs became extinct, but eventually they did.

“It’s another piece in the puzzle, another piece that enables us to establish why it became extinct.

“This is really important in our understanding of the influence of climate change on us today [and] is trying to understand the actual things that might happen in the ocean and in the atmosphere when the climate does change.

“Because climate was changing throughout this Cretaceous period and one of the hypotheses that has been suggested for the extinction of some of the marine animals and the Cretaceous were changes in the chemistry of the ocean and these chemical changes are already being found in the oceanic conditions that we see in the ocean today.”

Even though it is the most complete ichthyosaur fossil ever found in Aotearoa, it is only a partial specimen.

“It’s a new member of the ichthyosaur club, but it is not complete enough to give it a name,” Scofield said.

The fossil is distinct from other ichthyosaurs discovered in Australia. It has a smaller pelvis bone than other fossils found around the world.

Researchers managed to date the fossil to 95 million years ago by analysing the layer of rock where it was discovered.

“It was in the right layer and the fossils around it were of known ages.”

Scofield said the high country where the fossil was discovered was very poorly explored and could yield more groundbreaking discoveries.

Ichthyosaurs, which grew up to 26m long, first appear in the fossil record from around 250 million years ago, surviving until about 95 million years ago.

- RNZ