This extinct dolphin had tusks that fish had better avoid

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

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

“Mentally, I just couldn’t figure out what might need teeth like that,” said Dr. Cost.

The fossil dolphin’s dentition was unlike anything seen in living cetaceans. While modern dolphins are armed with a snout full of cone-shaped teeth perfectly calibrated to catch fish, this creature possessed several large teeth protruding from the end of its snout. Instead of tapering down into fangs, these teeth were spread out horizontally like the blade of a spade.

This is according to an article published in the magazine on Wednesday Procedures of the Royal Society Bdescribed Dr. Coste and her colleagues identified the snaggletoothed dolphin as a unique species, Nihohae matakoi. The curious cetacean genus, Nihohae, is a combination of the Maori words for “teeth” and “slashing.”

True tusks are defined as continuously growing teeth protruding from the mouth, and narwhals are the only living cetaceans to have them. Nihohae’s protruding teeth were deeply rooted in its skull, preventing them from continuing to grow throughout the animal’s life. As a result, Nihohae’s teeth more closely resemble the tusk protrusions on the lower jaws of male beaked whales, which use these teeth to grapple over females.

To determine how Nihohae wielded its tusks, Dr. Coste and her colleagues view several teeth under a scanning electron microscope. Surprisingly, the researchers found few signs of wear.

This meant that Nihohae was unlikely to use its tusks to fight rivals for partners. It also cast doubt on another hypothesis that Nihohae used its teeth to search for prey through the sandy sea floor. “Sand is really abrasive and will absolutely destroy your teeth, but there are literally no scratches on these teeth,” said Dr. Cost.

The horizontal orientation of the teeth also made them a poor tool for capturing prey. While other fossil dolphins’ teeth interlocked to trap fish inside, Nihohae’s splayed teeth wouldn’t have been useful for that task. They were also nearly flat, so Nihohae would have had a hard time biting into anything.

Since no other dolphin possessed teeth like Nihohae’s, the researchers scoured the rest of the animal kingdom for similar anatomy. This led them to sawfish, which flick their tooth-studded saws to injure or stun prey before sucking it up whole.

Dr. Coste and her colleagues hypothesize that Nihohae, whose unfused vertebrae likely enabled a wide range of neck movements, hunted in a similar fashion, swinging its head to skewer or stun squid and other gentle sea creatures. Then it would swallow the staggered prey whole.

“You can imagine these dolphins swimming up to a shoal of squid and thrashing their heads wildly,” said Dr. Cost.

This hunting style seems plausible, according to Robert Boessenecker, a paleontologist at the College of Charleston in South Carolina who was not involved in the new study.

“Given that the teeth in Nihohae are splayed to the side, that’s a pretty good indication that there was lateral movement, similar to the sweeping of a sawfish’s snout,” said Dr. Boessenecker, who has studied others toothy dolphin fossils from both South Carolina and New Zealand.

Dr. Coste hopes that further research of Nihohae’s tusks and future fossil finds will shed additional light on the diversity of ancient dolphin hunting techniques.