Miniature dolphins without any teeth swam in the Atlantic Ocean 30 million years ago, according to a newly discovered fossil.
Scientists reported in the journal Proceedings of the Royal Society B that a fossil from South Carolina paints a picture of a dwarf dolphin that vacuumed up its meals of small fish and squid, instead of grabbing and holding onto fish with its teeth like modern dolphins.
This new extinct species, called Inermorostrum xenops, “possesses adaptations for suction feeding: toothlessness and a shortened rostrum,” the study says, referring to its snout. It may have also had “enlarged lips” and whiskers to get the job done.
The idea of muscular, fleshy lips comes from impressions in the fossil for where there were once arteries feeding the tissue.
The researchers note that suction-feeding traits “independently evolved several times” within these groups of marine animals.
Researchers dated the specimen to 30 million years ago, putting it in the middle of the Oligocene epoch, which occurred late in the Paleogene. The Paleogene was the period that followed the dinosaur-infested Cretaceous period — with the mass extinction event that wiped out those creatures occurring about 66 million years ago, at the boundary line where the Cretaceous ended and the Paleogene began.
The team was working with just a skull fossil that had been discovered in a river near Charleston, according to a report from Agence France Presse. But from the remains of its head the scientists were able to estimate that the extinct dolphin was about three feet long.
An illustration shows what an extinct kind of dolphin may have looked like, with its miniature size and toothless grin. Photo: Robert Boessenecker
That’s compared to bottlenose dolphins, which swim the waters around South Carolina now, as part of their enormous range around the world, and are between 6 feet and 12.5 feet long. The U.S. National Oceanic and Atmospheric Administration says these modern dolphins have short, thick beaks. They are born with some hairs on those beaks, but they lose them shortly afterward, which would set them apart from the whiskered Inermorostrum. And instead of sucking up all of their prey, bottlenose dolphins might “employ a feeding strategy called ‘fish whacking’ where they strike a fish with their flukes and knock it clear out of the water.”
It took only 4 million years — a relatively short time in the grand scheme of evolutionary history — for the Inermorostrum to evolve into toothless, suction-feeding dolphins from their whale ancestors who had teeth on their tops and bottoms of their mouths, lead study author Robert Boessenecker told AFP. Its snout and mouth shrank and its lips became more muscular.
“This last feature is perhaps the most critical,” Boessenecker said. “Short snouts typically occur in [toothed whales] that are adept at suction feeding — the smaller the oral opening, the greater the suction.”
Its nose bent downward, so it might have looked for its soft prey on the ocean floor.
The extinct mini-dolphin was an early version of the toothed whales. In addition to other dolphins, modern examples include the sperm whale, porpoises and the killer whale — also known as an orca.
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