There's new insights into New Zealand's ancient fauna from a 20-year dig.

An international team of palaeontologists researching the St Bathans fossil site in Central Otago have concluded kakapo, small wrens, bats and freshwater limpets arrived well before other well known species - like kiwi and moa.

Canterbury Museum Senior Natural History Curator Paul Scofield says they also uncovered signs of other surprising animals living here.

"We had two species of crocodile - and we believe that they most likely became extinct at the beginning of the ice age about two or three years ago."

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