University of Otago researchers say the dolphin dubbed Papahu taitapu lived 19 million to 22 million years ago, the Otago Daily Times reported Wednesday.
The skull, one jaw, and a few other bones were found in marine sedimentary rocks in the country's South Island, and only a single specimen had been found so far, the researchers said.
The fossil skull suggests Papahu was about 6 feet long, about the same as today's common dolphin, and had many simple conical teeth like most living dolphins, the researchers said.
Features of the Papahu skull are distinct from all previously-reported fossils, they said.
"When we compared Papahu with both modern and fossil dolphins we found that it belongs in a diverse and structurally variable group of ancient dolphins that evolved and spread world-wide 19 million to 35 million years ago," Otago geology Professor Ewan Fordyce said. "All of those ancient dolphins including Papahu and others, such as shark-toothed dolphins, are now extinct."
"They have been replaced by the 'modern' dolphins and toothed whales, which diversified within the last 19 million years," he said.