Date:

Ancient Bony Fish Forces Rethink of How Sharks Evolved

Sharks’ non-bony skeletons were thought to be the template before bony internal skeletons evolved, but a new fossil discovery suggests otherwise.

The discovery of a 410-million-year-old fish fossil with a bony skull suggests the lighter skeletons of sharks may have evolved from bony ancestors, rather than the other way around.

- Advertisement -

Sharks have skeletons made cartilage, which is around half the density of bone. Cartilaginous skeletons are known to evolve before bony ones, but it was thought that sharks split from other animals on the evolutionary tree before this happened; keeping their cartilaginous skeletons while other fish, and eventually us, went on to evolve bone.

Now, an international team led by Imperial College London, the Natural History Museum and researchers in Mongolia have discovered a fish fossil with a bony skull that is an ancient cousin of both sharks and animals with bony skeletons. This could suggest the ancestors of sharks first evolved bone and then lost it again, rather than keeping their initial cartilaginous state for more than 400 million years.

Lead researcher Dr Martin Brazeau, from the Department of Life Sciences at Imperial, said: “It was a very unexpected discovery. Conventional wisdom says that a bony inner skeleton was a unique innovation of the lineage that split from the ancestor of sharks more than 400 million years ago, but here is clear evidence of bony inner skeleton in a cousin of both sharks and, ultimately, us.”

Most of the early fossils of fish have been uncovered in Europe, Australia and the USA, but in recent years new finds have been made in China and South America. The team decided to dig in Mongolia, where there are rocks of the right age that have not been searched before.

- Advertisement -
Virtual three-dimensional model of the braincase of Minjinia turgenensis generated from CT scan. Inset shows raw scan data showing the spongy endochondral bone inside. – Image Credit : Imperial College London/Natural History Museum

They uncovered the partial skull, including the brain case, of a 410-million-year-old fish. It is a new species, which they named Minjinia turgenensis, and belongs to a broad group of fish called ‘placoderms’, out of which sharks and all other ‘jawed vertebrates’ – animals with backbones and mobile jaws – evolved.

When we are developing as foetuses, humans and bony vertebrates have skeletons made of cartilage, like sharks, but a key stage in our development is when this is replaced by ‘endochondral’ bone – the hard bone that makes up our skeleton after birth.

Previously, no placoderm had been found with endochondral bone, but the skull fragments of M. turgenensis were “wall-to-wall endochondral”. While the team are cautious not to over-interpret from a single sample, they do have plenty of other material collected from Mongolia to sort through and perhaps find similar early bony fish.

And if further evidence supports an early evolution of endochondral bone, it could point to a more interesting history for the evolution of sharks.

Dr Brazeau said: “If sharks had bony skeletons and lost it, it could be an evolutionary adaptation. 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.”

IMPERIAL COLLEGE LONDON

Header Image Credit : Public Domain

- Advertisement -

Stay Updated: Follow us on iOS, Android, Google News, Facebook, Instagram, Twitter, Threads, TikTok, LinkedIn, and our newsletter

spot_img
Mark Milligan
Mark Milligan
Mark Milligan is multi-award-winning journalist and the Managing Editor at HeritageDaily. His background is in archaeology and computer science, having written over 8,000 articles across several online publications. Mark is a member of the Association of British Science Writers (ABSW), the World Federation of Science Journalists, and in 2023 was the recipient of the British Citizen Award for Education, the BCA Medal of Honour, and the UK Prime Minister's Points of Light Award.
spot_img
spot_img
spot_img

Mobile Application

spot_img

Related Articles

Ornately decorated sarcophagus unearthed in “City of Gladiators”

Excavations in Stratonikeia, located in the Yatağan district of Muğla in southwestern Türkiye, have unearthed a 2,000-year-old sarcophagus from the Roman Imperial Age.

The mystery of a 1940’s Ford Woody discovered on USS Yorktown shipwreck

During a recent expedition aboard NOAA Ship Okeanos Explorer for the Papahānaumokuākea ROV and Mapping project, NOAA Ocean Exploration and its partners discovered a 1940s Ford Woody on the wreck of the USS Yorktown.

Roman phallus found at frontier fortress

Excavations at Vindolanda near Hadrian’s Wall have unearthed a miniature phallus pendant.

Ancient underground chamber discovery in Cnoc Ard

A construction project in Cnoc Ard (Knockaird) on the Isle of Lewis has revealed a stone-built underground chamber, later identified by archaeologists as a Late Iron Age souterrain.

Caral burial unearthed at Áspero: Elite woman found remarkably preserved

Archaeologists from the Caral Archaeological Zone (ZAC), led by Dr. Ruth Shady Solís from the Ministry of Culture, have discovered a well-preserved burial at the Áspero archaeological site in Barranca Province, Peru.

Mesolithic figurine found in Damjili Cave offers new clues to Neolithic transition

A stone figurine discovered in Damjili Cave, western Azerbaijan, is providing archaeologists with new insights into the cultural and symbolic transition from the Mesolithic to Neolithic in the South Caucasus.

Bite marks confirm gladiators fought lions at York

A recent study published in PLOS One has identified bite marks on human remains excavated from Driffield Terrace, a Roman cemetery on the outskirts of York, England.

Treasures of the Alanian culture found in Alkhan-Kala necropolis

Archaeologists have discovered an intact burial mound containing the tomb of an Alanian elite during excavations at Alkhan-Kala west of Grozny, Chechnya.