Marine Biologists Recently Spotted A Dolphin With Human-Like ‘Thumbs’

Published December 15, 2023

The dolphin's deformed flippers are likely the result of a genetic defect, but the creature is "thriving" nonetheless.

Dolphin With Thumbs

Alexandros Frantzis/Pelagos Cetacean Research InstituteResearchers spotted the unusual dolphin twice this summer while conducting surveys near Greece.

While observing marine life in the Gulf of Corinth near Greece last summer, researchers spotted a dolphin that appeared to have thumbs on its flippers. The defect seems to be genetic, but fortunately the researchers have given the dolphin’s general health a “thumbs up.”

Alexandros Frantzis, the scientific coordinator and president of the Pelagos Cetacean Research Institute, told Live Science that the dolphin was seen “swimming, leaping, bow-riding, [and] playing” and seemed perfectly capable with keeping up with its pod, despite its unusual appendages.

But though the dolphin with thumbs seems to be “thriving,” its deformed flippers are highly unusual.

“It was the very first time we saw this surprising flipper morphology in 30 years of surveys in the open sea and also in studies while monitoring all the stranded dolphins along the coasts of Greece for 30 years,” Frantzis said.

So what happened to the dolphin to give it thumbs?

As the researchers explained, it doesn’t appear that the creature is suffering from any kind of illness. Rather, its unusual flippers are probably the result of a genetic defect that occurred during its development in the womb.

Dolphin Thumbs

Alexandros Frantzis/Pelagos Cetacean Research InstituteAnother angle of the dolphin with thumbs.

“The fact that this irregularity is found in both flippers of the dolphin and no injuries or skin lesions are present explains why this could not be an illness, but an expression of very rare genes,” Frantzis explained to USA TODAY.

It’s possible, he theorized, that it’s the result of “constant interbreeding.”

In fact, all dolphins technically have thumbs — they’re just not visible on the surface. Dolphins and other cetaceans, like whales and porpoises, have finger bones that make up a human-like “hand,” but they’re generally encased in a soft-tissue flipper.

During a dolphin’s development in the womb, these “fingers” are surrounded by cells. Normally, these cells merge together to create the dolphin’s flippers (in contrast to human fetuses, which develop “paddle-like” hands in the womb before the cells between the fingers die off prior to birth).

But it seems like something went awry during this dolphin’s development. As Lisa Noelle Cooper, an associate professor of mammalian anatomy and neurobiology at the Northeast Ohio Medical University, explained to Live Science: “It looks to me like the cells that normally would have formed the equivalent of our index and middle fingers died off in a strange event when the flipper was forming while the calf was still in the womb.”

Striped Dolphins

OceanCare/Wikimedia CommonsStriped dolphins, like the dolphin with “thumbs,” seen jumping out of the water in the Gulf of Corinth.

The dolphin is one of roughly 1,300 striped dolphins (Stenella coeruleoalba) that live in the Gulf of Corinth. Isolated from other dolphins in the Mediterranean, they’ve been under observation by the Pelagos Cetacean Research Institute since 1995.

The striped dolphins live alongside other dolphin species, like common dolphins and Risso’s dolphins, in a “permanent mixed-species dolphin society,” according to USA Today. Though they’re all dolphins, the genetic difference between the species is akin to humans living with chimpanzees and gorillas.

But the discovery of the dolphin with deformed flippers is not a sign of a new dolphin species that’s suddenly growing human-like thumbs. In fact, its thumbs don’t move at all.

“The hook-shaped ‘thumb’ may have some bone inside of it, but it certainly isn’t mobile,” Cooper noted. “[N]o cetaceans have mobile thumbs.”


After reading about the dolphin with “thumbs” that was spotted off the coast of Greece, discover the story of the rare, all-white albino panda that was spotted in China. Or, learn about the surprising study that found that dolphins can recognize their friends — by the taste of their urine.

author
Kaleena Fraga
author
A staff writer for All That's Interesting, Kaleena Fraga has also had her work featured in The Washington Post and Gastro Obscura, and she published a book on the Seattle food scene for the Eat Like A Local series. She graduated from Oberlin College, where she earned a dual degree in American History and French.
editor
Cara Johnson
editor
A writer and editor based in Charleston, South Carolina and an assistant editor at All That's Interesting, Cara Johnson holds a B.A. in English and Creative Writing from Washington & Lee University and an M.A. in English from College of Charleston and has written for various publications in her six-year career.
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Fraga, Kaleena. "Marine Biologists Recently Spotted A Dolphin With Human-Like ‘Thumbs’." AllThatsInteresting.com, December 15, 2023, https://allthatsinteresting.com/dolphin-with-thumbs. Accessed June 25, 2024.