| A newly discovered primordial fish with small skull and jaw bones and a bony skeleton is the prototype species for all vertebrates, say researchers. |
The ancestor of all creatures with jaws and a backbone was not a sleek, shark-like beast but a toothless, armoured fish, say researchers, in a finding that rewrites all of evolutionary history.
Dr Brian Choo, from the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, and colleagues report their findings today in the journal Nature.
The researchers report their discovery of a 419-million-year-old fish fossil in China, which they say disproves the long-held theory that modern animals with bony skeletons (osteichthyans) evolved from a shark-like creature with a frame made of cartilage.
The osteichthyan group includes most living fish, humans and other land animals with limbs.
| Related articles |
This meant that we osteichthyans would have evolved our bony frames from scratch while the group that includes sharks, rays and ratfish retained their ancestral cartilage skeletons.
But the new find of a primordial fish with a complex arrangement of small skull and jaw bones revealed a missing branch on the evolutionary tree and showed that a bony skeleton was in fact the prototype for all vertebrates, say Choo and colleagues.
"This astounding discovery does throw a spanner in the works of some long-held ideas about vertebrate evolution," says Choo.
"The implications are clear: ostheichthyans did not independently acquire their bony skeletons, they simply inherited them" from their ancestors -- heavily-armoured fish known as placoderms that are accepted to be the most primitive members of the jawed vertebrate family.
This meant that sharks and rays, instead of being the archetypal vertebrates, shed the common ancestor's bony plates as they evolved, say the researchers.
The newly discovered creature, dubbed Entelognathus primordialis (meaning primordial complete jaw) was a type of placoderm that lived in the seas of China in the Late Silurian period from about 423 million to 416 million years ago.
The weird-looking animal, whose near-complete fossil was dug up near the southern Chinese town of Qujing, was about 20 centimetres long, had a heavily armoured head and trunk and a scaly tail.
It had jaws but no teeth and tiny eyes set in large, bony goggles. It was not a direct ancestor of today's jawed vertebrates, but an extinct "close nephew" of our common forefather that shared many of its characteristics, according to Choo.
"I was completely blown away upon seeing this fossil for the first time, even more so as the full implications started to sink in," he says.
"Every now and then you are confronted with jaw-dropping specimens like Lucy the Australopithecus (an extinct, upright-walking hominid) or the first batch of Chinese feathered dinosaur, unleashing a flood of new information that greatly clarifies our view of the distant past and often forces us to rethink what we thought we knew about evolution.
"A little fish called Entelognathus now joins the ranks of these exceptional fossil discoveries."
"This is the most exciting news in palaeontology since Archaeopteryx or Lucy. A true 'missing link' fossil fish has been found in China, dated at 425 million years old, which finally solves an age old problem about the origin of modern fishes," says palaeontologists Matt Friedman from the University of Oxford and Martin Brazeau from Imperial College London and Naturalis Biodiversity Center in the Netherlands.
"We now know that ancient armoured placoderms gave rise to the modern fish fauna as we know it."
However, the rearranged family tree is not yet quite conclusive, write the authors of a related News & Views article. There remains a chance that E. primordialis evolved its jaw independently from the bony fish, so that we did not inherit it, and the resemblance is an illusion.
SOURCE ABC Science
| By 33rd Square | Subscribe to 33rd Square |
0 comments:
Post a Comment