Ancient New Zealand dolphin related to Ganges river dolphin

A long extinct New Zealand dolphin was linked to India's endangered Ganges river dolphin, researchers in New Zealand said on Tuesday.

The newly-described ancient marine dolphin fossil, found in the Waitaki area on the east of the South Island, was of the same "superfamily" as the Ganges river dolphin, said University of Otago researchers.

The fossil species, named Otekaikea huata, joined only a few other dolphins known from about 22.5 million to 24.5 million years ago, Ewan Fordyce, a professor, said in a statement.

At that time, New Zealand was a cluster of small low islands with extensive shallow warm seas.

In life, the fossil dolphin's skull was about 80 cm long, and its body around 2.6 metres.

"The fossil has a surprisingly long projecting tusk that became broken in life, but whether this was from fighting or feeding is uncertain. It's likely that it had four or more tusks in life, but these others weren't preserved," Fordyce said.

Otekaikea huata belonged to the once-diverse and widespread dolphin group called Platanistoidea, which is now extinct in the oceans and is represented only by the endangered Ganges river dolphin and Indus river dolphin subspecies, Xinhua news agency reported.

"Our study is one of several showing that the South Asian river dolphin lineage was more diverse in the past," he said.

"It is not clear why this lineage became extinct in the oceans, but it could have been due to long-term climate change and competition from later-evolving ocean dolphins."