Toothless, dwarf dolphin, a case study in evolution

August 23, 2017 by Marlowe Hood
A life restoration of Inermorostrum xenops dolphins

Scientists on Wednesday unveiled an extinct species of toothless, whiskered and objectively cute mini-dolphin that plied Earth's oceans some 30 million years ago.

With only a fossilised cranium—found in a river near Charleston, South Carolina—to work with, the researchers were able to reconstruct the snub-nosed mammal's evolutionary saga, describe its facial features and figure out what it snacked on.

Just over a metre (three feet) from snout to tail, Inermorostrum xenops was half the size of the common bottlenose dolphin.

Ironically, the pint-size Flipper was an early offshoot from one of the two main groupings of cetaceans called Odontoceti, or "toothed whale", that includes and orca.

This group also developed a radar-like capacity to navigate and detect objects by emitting sounds, called echolocation.

The other branch, , are filter feeders that strain huge volumes of ocean water to net tiny, shrimp-like krill or plankton—think humpback or the gargantuan blue.

"Inermorostrum took only four million years to evolve from ancestral whales with precisely occluding teeth"—matching top and bottom—"into a toothless, suction feeding specialist," explained Robert Boessenecker, a professor at the College of Charleston and lead author of a study in the British Royal Society journal Proceedings B.

During those four million years—a brief interlude on the evolutionary clock—I. xenops lost its pearly whites, saw its snout and mouth shrink and developed super muscular lips.

"This last feature is perhaps the most critical," said Boessenecker, who deduced the dolphin's powerful smackers from a series of deep artery channels clearly designed to nourish extensive soft tissue.

"Short snouts typically occur in Odontoceti that are adept at suction feeding—the smaller the oral opening, the greater the suction," he said in a statement.

Absent dentition, I. xenops' diet would have consisted exclusively of small fish, squid and other soft-bodied creatures. Because its nose was bent downward, the researchers suspect it prowled the ocean floor in search of prey.

The dwarf dolphins were not the only "toothed " undergoing rapid evolution at that time.

During the Oligocene age, 25 to 35 million years ago, other echolocating cetaceans developed long, toothy snouts specialised in catching fish.

The researchers also found that both short and long snouts evolved independently numerous times, suggesting that natural selection is not an arbitrary process.

Some dolphins, such as the modern bottlenose, settled on a happy medium between the extremes, "the optimum length as it permits both fish catching and suction feeding," Boessenecker added.

Explore further: Ancient South Carolina whale yields secrets to filter feeding's origins

More information: Proceedings of the Royal Society B(2017). Doi: 10.1098/rspb.2017.0531

Related Stories

Baleen whales' ancestors were toothy suction feeders

May 11, 2017

Modern whales' ancestors probably hunted and chased down prey, but somehow, those fish-eating hunters evolved into filter-feeding leviathans. An analysis of a 36.4-million-year-old whale fossil suggests that before baleen ...

Researchers identify new NZ fossil whale species

September 11, 2015

University of Otago palaeontology researchers are continuing to rewrite the history of New Zealand's ancient whales by describing two further genera and three species of fossil baleen whales.

One amino acid, a whale of a difference

July 18, 2017

A single amino-acid variation in a key receptor in whales may help explain why some species of cetaceans evolved sleek, muscular bodies to hunt fish and seals, while others grow to massive sizes by filter-feeding on large ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

EPA adviser is promoting harmful ideas, scientists say

March 22, 2019

The Trump administration's reliance on industry-funded environmental specialists is again coming under fire, this time by researchers who say that Louis Anthony "Tony" Cox Jr., who leads a key Environmental Protection Agency ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.