The pygmy right whale, an elusive baleen that rarely comes to shore, is now thought to be the last living descendant of the long extinct group of whales, according to a study published on Tuesday in the Proceedings of the Royal Society B.

The discovery may help to explain the pygmy whale's unique appearance; the comparatively small whale (adult pygmy whales typically only grow to about 21 feet long) has a distinct, downturned snout that looks almost like a permanently etched-in frown.

According to the website LiveScience, DNA analysis had previously suggested that the whales were related to modern baleen whales, such as the blue whale and humpback whales, and only began to separate from them between 17 million and 25 million years ago.

The new study, which examined pygmy whale fossil fragments and skull bones and contrasted them against those of other ancient cetaceans, found that the pygmy whale more closely resembled a group of whales called cetotheres, thought to have vanished over two million years ago, said Felix Marx, a paleontologist at New Zealand's University of Otago. Cetotheres, a group that includes the bowhead whale, are thought to have arisen 15 million years ago.

"The living pygmy right whale is, if you like, a remnant, almost like a living fossil," said Marx. "It's the last survivor of quite an ancient lineage that until now no one thought was around."

Yet despite the finding, Marx said that researchers were unable to find any evidence of how the pygmy whale had evolved.

Pygmy whales are not often studied by researchers and relatively little is known about them, because they seldom appear at sea. They are known to reside in the Southern Hemisphere, but have only been sighted "a few dozen times," reported NBC.

Consequently, most information about them comes from fossils that have washed up on shore.  Marx said that the discovery might help to explain their evolution and give scientists some insight into the ancient species’ social structure.