Fish Fossil Helps to Demonstrate How Fins Turned into Hands

A team of international scientists including researchers from Flinders University in Adelaide (South Australia) and the Université du Québec à Rimouski (Canada), have scanned the fossilised remains of an ancient fish with tetrapod tendencies to reveal evidence of how the limbs of fish evolved into the terrestrial appendages of land animals.  The fossilised remains date from the Late Devonian and are approximately 380 million years old.  The fossil is a specimen of Elpistostege (E. watsoni), the discovery of a much more complete skeleton of this strange animal gave the researchers the opportunity to analyse the body plan of this predator in much greater detail than previously.

A Near Complete Specimen of Elpistostege watsoni with Accompanying Line Drawing

Elpistostege watsoni fossil with interpretive drawing and life reconstruction.

The near complete Elpistostege specimen with line drawing showing the outline of the skeleton and a life reconstruction.  The research was conducted on a fossil specimen that had been discovered in 2010.

Picture Credit: South Australia Leads/Flinders University

Strategic Professor in Palaeontology (Finders University), Professor John Long, announced the discovery of the near complete fossil specimen in the journal “Nature”.  Commenting on the significance of the fossil find, he stated that the specimen “reveals extraordinary new information about the evolution of the vertebrate hand.”

High Energy X-Rays to Assess Fin Structure

The research team bombarded the fossil specimen with high energy X-rays to reveal the presence of limb and wrist bones hidden in the fins.  Evidence of finger-like bones could also be made out.

The Professor added:

“This is the first time that we have unequivocally discovered fingers locked in a fin with fin-rays in any known fish.  The articulating digits in the fin are like the finger bones found in the hands of most animals.  This finding pushes back the origin of digits in vertebrates to the fish level and tells us that the patterning for the vertebrate hand was first developed deep in evolution, just before fishes left the water.”

A Life Reconstruction of the Late Devonian Elpistostege

Elpistostege life reconstruction.

A life reconstruction of Elpistostege.

Picture Credit: Miguasha National Park/Johanne Kerr and François Miville-Deschênes

The high resolution scans revealed the presence of a humerus (upper arm bone), the radius and ulna (the two bones from the forearm), carpal bones from the wrist and the presence of bones that resembled digits.  The fossil specimen measures 1.57 metres in length.  It comes from exposures of the Escuminac Formation located in the Canadian province of Quebec.  The strata represent a brackish water, estuarine environment and palaeontologists have long speculated that such a habitat may have been one of the driving forces behind the evolution of limbs capable of terrestrial locomotion in certain types of ancient fish.  The teeth in the broad jaw suggest that Elpistostege was an apex hypercarnivore, but whether it fed on other fish or ventured out onto land to grab insects and arthropods on the shore (as indicated by the position of the eyes at the top of the head suggesting an ambush predator), remains unknown.

Co-author of the scientific paper Richard Cloutier (Université du Québec à Rimouski), commented that over the last ten years or so, fossils representing the fish-to-tetrapod transition had helped palaeontologists to gain a better understanding about this important stage in vertebrate evolution.

He added:

“The origin of digits relates to developing the capability for the fish to support its weight in shallow water and for short trips out on land.  The increased number of small bones in the fin allows more planes of flexibility to spread out the weight through the fin.”

In previous studies, Dr Cloutier had postulated that Elpistostege might represent the most primitive tetrapod known to science, an accolade currently held by the closely related Tiktaalik, fossils of which come from northern Canada (Ellesmere Island).

Australian Professor John Long has dedicated much of his academic career to studying Devonian fish and the early stages of the evolution of the modern tetrapod body plan.

Here are some blog articles that provide more details of his research: The Early Evolutionary History of Sharks.

A Placoderm “Platypus”: Ancient Placoderm from Australia.

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