The waters off New Zealand 25 million years ago were home to early baleen whales, megatooth sharks and human-size penguins. Now researchers are adding a bizarre dolphin to the mix that may have used tusklike teeth to thrash prey into submission.

The dolphin’s nearly complete skull was collected in 1998, from a cliff side in the Otago region of New Zealand’s South Island. The specimen ended up in the University of Otago Geology Museum’s collection. Two decades later, Amber Coste, who was completing her Ph.D. in paleontology, stumbled upon the strange skull.

“Mentally, I just couldn’t figure out what could possibly need teeth like that,” Dr. Coste said.

The fossil dolphin’s dentition was unlike anything seen in living cetaceans. While modern dolphins are armed with a snoutful of cone-shaped teeth perfectly calibrated to snap up fish, this creature possessed several large teeth that protruded out of the end of its snout. Instead of tapering downward into fangs, these teeth were splayed out horizontally like the blade of a spade.

In a paper published Wednesday in the journal Proceedings of the Royal Society B, Dr. Coste and her colleagues described the snaggletoothed dolphin as a unique species, Nihohae matakoi. The curious cetacean’s genus, Nihohae, is a combination of the Maori words for “teeth” and “slashing.”