Ancient marine reptile from New Zealand is oldest found in southern hemisphere

A fossil from New Zealand’s south island has been identified as a prehistoric marine reptile which lived 246 million years ago. The new discovery upends previous theories about the distribution of these earliest marine reptiles.

Fossil vertebra in hand
Original fossil of the New Zealand nothosaur vertebra. Credit: Benjamin Kear.

The creature from New Zealand lived right at the dawn of the dinosaurs during the Triassic period (252–201 million years ago). It is known from a single dorsal vertebra. The specimen belongs to the oldest of this type of marine reptile ever found in the southern hemisphere.

Despite being uncovered in 1978, the significance of the fossil was not understood until a new study which has been published in the Current Biology journal.

The animal belongs to a group of ancient reptiles called nothosaurs. Nothosaurs are themselves part of a larger group called sauropterygians including the more well-known plesiosaurs – a type of long-necked, flippered marine reptile which died out along with the non-avian dinosaurs 66 million years ago.

Palaeontologists believe nothosaurs to be ancestors of plesiosaurs.

Nothosaurs usually grew to about 3 metres in length and had webbed feet – a clue to their aquatic lifestyle.

“The nothosaur found in New Zealand is more than 40 million years older than the previously oldest known sauropterygian fossils from the southern hemisphere,” explains lead author Dr Benjamin Kear from The Museum of Evolution at Uppsala University, Sweden.

“We show that these ancient sea reptiles lived in a shallow coastal environment teeming with marine creatures within what was then the southern polar circle.”

The New Zealand nothosaur is close in age to the world’s oldest which date to about 248 million years ago. These fossils are from the low northern latitudes of the ancient Panthalassa super ocean which encompassed Earth until about 190 million years ago.

It’s still debated how these ancient reptiles first emerged and migrated.

Some theories suggest nothosaurs reached distant parts of the Panthallassic Ocean along coastlines, inland seaways or ocean currents.

The New Zealand nothosaur challenges these hypotheses.

“Using a time-calibrated evolutionary model of sauropterygian global distributions, we show that nothosaurs originated near the equator, then rapidly spread both northwards and southwards at the same time as complex marine ecosystems became re-established after the cataclysmic mass extinction that marked the beginning of the Age of Dinosaurs,” Kear says.

New Zealand 250 million years ago was underwater and within the polar circle.

“The beginning of the Age of Dinosaurs was characterised by extreme global warming, which allowed these marine reptiles to thrive at the South Pole. This also suggests that the ancient polar regions were a likely route for their earliest global migrations, much like the epic trans-oceanic journeys undertaken by whales today,” Kear says.

“Undoubtedly, there are more fossil remains of long-extinct sea monsters waiting to be discovered in New Zealand and elsewhere in the southern hemisphere.”

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