Researchers have revealed new insights into how the human hand evolved from fish fins based on their analysis of an ancient fossil found in Miguasha, Canada.
Palaeontologists, including those from Flinders University in Australia, said the fish specimen has yielded the missing evolutionary link in the transition from fish to four legged animals.
They said this happened during the Late Devonian period, millions of years ago, as fish began to foray in habitats such as shallow water and land.
The study, published in the journal Nature, noted that the 1.57 metre long fossil shows the complete arm -- pectoral fin -- skeleton for the first time in any elpistostegalian fish.
Using high energy X-Ray CT-scans, the scientists assessed the skeleton of the pectoral fin, revealing the presence of a humerus (arm), radius and ulna (forearm), rows of carpus (wrist) and phalanges organized in digits (fingers).
"This is the first time that we have unequivocally discovered fingers locked in a fin with fin-rays in any known fish," said John Long, study co-author from Flinders University Professor.
"The articulating digits in the fin are like the finger bones found in the hands of most animals," Long said.
The finding, according to the researchers, pushes back the origin of fingers in vertebrates to the fish level.
They said it also reveals that the patterning for the vertebrate hand was first developed deep in evolution, just before fishes left the water.
The evolution of fishes into four-legged vertebrates was one of the most significant events in the history of life, the study noted.
With this adaptation, the scientists said, vertebrates, or back-boned animals, were then able to leave the water and conquer land.
To complete this transition, they said, one of the most significant changes was the evolution of hands and feet.
"The origin of digits relates to developing the capability for the fish to support its weight in shallow water or for short trips out on land. The increased number of small bones in the fin allows more planes of flexibility to spread out its weight through the fin," said study co-author Richard Cloutier from the Universite du Quebec in Canada.
"The other features the study revealed concerning the structure of the upper arm bone or humerus, which also shows features present that are shared with early amphibians," Cloutier said.
He said elpistostege is the closest scientists can get to a true 'transitional fossil' -- an intermediate between fishes and tetrapods.
According to the scientists, these animals were the largest predators living in a shallow marine to estuarine habitat of Quebec about 380 million years ago.
They had powerful sharp fangs in their mouth and may have fed upon several of the larger extinct lobe-finned fishes found fossilised in the same deposits, the researchers noted.
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