Quantcast
Environmental News for a Healthier Planet and Life

‘Surprising’ Fossil Discovery Could Rewrite Shark Evolution Story

Science
‘Surprising’ Fossil Discovery Could Rewrite Shark Evolution Story
Sharks, unlike other large fish, have skeletons made out of cartilage. Ryan Espanto / CC BY 2.0

A recent fossil discovery could overturn the way scientists think about shark evolution.


Sharks are different from other large fish like salmon or tuna in that they have softer, non-bony skeletons made out of a material called cartilage. It was previously thought that sharks split off from a common ancestor with a cartilage skeleton, before the bony skeletons favored by other fish and all terrestrial vertebrates evolved. But now, researchers have uncovered a fossil that is a common ancestor of both sharks and later fish, and has a bony skull.

"This fossil is probably the most surprising thing I have ever worked on in my career," study first author and Imperial College London senior lecturer D.r Martin Brazeau told The Guardian. "I never expected to find this."

The fossil, described in Nature Ecology and Evolution Monday, was dug up in western Mongolia in 2012. It is about 410 million years old and belongs to a group of fish called placoderms that are a common ancestor of sharks and all "jawed vertebrates," animals with jaws and backbones, an Imperial College London press release explained.

Until now, placoderm fossils had turned up with armored outsides but inner skeletons made of cartilage, enforcing the idea that sharks split from these ancient fish before bony fish evolved, according to The Guardian. But the new fossil, which consisted of a partial skull roof and brain case, was "wall-to-wall endochondral," or bone, according to the press release.

The fossil represents a new species of placoderm, which the researchers dubbed Minjinia turgenensis. Its discovery is part of a shift in where researchers search for the remains of early fish. Initial finds were dug up in Europe, Australia and the U.S., but now scientists are finding specimens in China and South America.

The bony placoderm was found by a team led by researchers from Imperial College London, London's Natural History Museum and Mongolia. They decided to dig in an area that had rocks of the right age that had never been examined before, and they still have many finds to sort through.

While the researchers cautioned that one fossil does not make a theory, they think it is now possible that sharks evolved bony skeletons and then "lost" them again. But for sharks, that "loss" would have been an evolutionary gain.

"If sharks had bony skeletons and lost it, it could be an evolutionary adaptation," Brazeau explained in the press release. "Sharks don't have swim bladders, which evolved later in bony fish, but a lighter skeleton would have helped them be more mobile in the water and swim at different depths. This may be what helped sharks to be one of the first global fish species, spreading out into oceans around the world 400 million years ago."

The bony placoderm is not the only evidence for this theory, Newsweek pointed out. In 2015, scientists announced a 380-million-year-old shark that had a skeleton made of cartilage, but with the remnants of what appeared to be bone cells.

University of Cambridge paleontologist Dr. Daniel Field, who was not involved with the research, told The Guardian that it was an example of the complexities of evolution.

"Evolutionary biologists were long guided by the assumption that the simplest explanation – the one that minimised the number of inferred evolutionary changes – was most likely to be correct. With more information from the fossil record, we are frequently discovering that evolutionary change has proceeded in more complex directions than we had previously assumed," he said.

Matthew Micah Wright / The Image Bank / Getty Images

By Deborah Moore, Michael Simon and Darryl Knudsen

There's some good news amidst the grim global pandemic: At long last, the world's largest dam removal is finally happening.

Read More Show Less

EcoWatch Daily Newsletter

Scrap metal is loaded into a shredder at a metal recycling facility on July 17, 2008 in Chicago, Illinois. Scott Olson / Getty Images

Hunger strikers in Chicago are fighting the relocation of a metal shredding facility from a white North Side neighborhood to a predominantly Black and Latinx community on the Southeast Side already plagued by numerous polluting industries.

Read More Show Less

Trending

A new UK study links eating meat with increased risks for heart disease, diabetes and more. nata_zhekova / Getty Images

The World Health Organization has determined that red meat probably causes colorectal cancer in humans and that processed meat is carcinogenic to humans. But are there other health risks of meat consumption?

Read More Show Less
A common cuttlefish like this can pass the "marshmallow test." Hans Hillewaert / CC BY-SA 4.0

Cuttlefish, marine invertebrates related to squids and octopuses, can pass the so-called "marshmallow test," an experiment designed to test whether human children have the self-control to wait for a better reward.

Read More Show Less
Yogyakarta Bird Market, Central Java, Indonesia. Jorge Franganillo / CC BY 2.0

By John R. Platt

The straw-headed bulbul doesn't look like much.

It's less than a foot in length, with subdued brown-and-gold plumage, a black beak and beady red eyes. If you saw one sitting on a branch in front of you, you might not give it a second glance.

Read More Show Less