Spectacular ‘missing link’ fossil fish found

A spectacular ‘missing link’ fossil has been unearthed in China, with palaeontologists declaring that the discovery of the 419 million-year-old armoured fish has solved an age-old debate in science.

The discovery of the fish fossil, called Entelognathus or ‘complete jaw’, was was big as finding the Higgs-Boson particle in physics because of its immense significance to the understanding of early vertebrate evolution, scientists said.

It was one of the most exciting fossil discoveries in the past century since Archaeopteryx, the first fossil to bridge the gap between dinosaurs and birds.

Zhu Min, lead author of the study and a scientist at the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, said: “It is beyond our wildest expectation if we stick to the available phylogenetic scenario. But the fossil provides evidence to force us to reconsider the existing hypothesis.”

Scientists have long debated which early backboned fishes were ancestral to modern fish. Living jawed fishes fall into two major groups: sharks, rays and chimaerids, and true bony fishes.

The Chinese scientists say the new discovery shows beyond doubt that an extinct group, called ‘placoderms’, were actually the ones that gave rise to all modern fishes.

One palaeontologist said that despite the fact that placoderms had dominated the "seas, lake and rivers of the world for more than 70 million years, almost no-one today would know the difference between a placoderm and a pachyderm” .

“Yet placoderms were truly pivotal to our distant deep evolution. They were innovators – the first creatures to evolve jaws, teeth and paired hind limbs or pelvic fins. They were also the first vertebrates to develop copulatory behaviour for mating.

“We must thank the placoderms for inventing the satisfying way we humans procreate.”

The Entelognathus fossil was discovered perfectly preserved in Yunnan in China and the results of the find were published on Thursday 26 September in the journal Nature. The report says the fossil shows an almost perfect intermediate condition between ancient placoderms and modern bony fishes.

At around 50 centimetres long, the fish had bony plates enclosing the head and front of its body, exactly like a placoderm. But its lower jaw is composed of a complex set of bones, unlike other placoderms, whose jaws were made of a single bone.

This pattern of bones in Entelognathus precisely matches those in the lower jaw of early fossil bony fishes, but Entelognathus also possessed special bones underneath its lower jaws called gulars, which are today only found in bony fishes.

The find is also the first appearance of a dentary bone, found in all bony fishes, amphibians, reptiles and mammals and is the same type of bone as found in the lower jaw of humans.

Scientists say the new discovery offers powerful new insights into the building of the human body plan, which began seriously with these ancient fossil fish.

An Australian coauthor on the paper, Brian Choo, has been working with Zhu in China for the past four years. He told a colleague: “This is a specimen that rips up the textbooks and says to you, ‘Look pal, this is how it really happened’.”