One area of active research in paleontology is the study of the evolution of fish to tetrapods. To this end, paleontologists are looking for ever more complete fish fossils in order to better understand the transition that took place between the fins and the members of the first terrestrial vertebrates. A few years ago, researchers found the fossil of a complete skeleton of Elpistostege, a member fish that lived during the Devonian. And his analysis allowed us to better understand the origin of the bone structure of vertebrate fingers.
A fish fossil Elpistostege found in Miguasha, Canada, revealed new clues to the evolution of the human hand from fish fins. An international team of paleontologists from Flinders University in Australia and the University of Quebec has revealed that the fish specimen, described in the journal Nature, established the missing evolutionary link in the fish-tetrapod transition, as fish began to evolve in habitats such as shallow water and land at the end of the Devonian millions of years ago.
A specimen to better understand the evolution of the hands of vertebrates
This 1.57 meter long complete fish shows the entire skeleton of the pectoral fin for the first time in an Elpistostegalian fish. Using a high-energy CT scan, the pectoral fin skeleton revealed the presence of a humerus (arm), radius and ulna (forearm), rows of carp (wrist) and phalanxes organized in extensions (fingers).
” We are announcing our discovery of a complete specimen of a tetrapod fish, called Elpistostege, which reveals extraordinary new information about the evolution of the hand of vertebrates. This is the first time that we have unequivocally discovered fingers locked in a fin with fin rays in all known fish. The articulated extensions in the fin are like the finger bones found in the hands of most animals “Explains paleontologist John Long.
Animation showing the complete fossilized skeleton found by the researchers, as well as a reconstruction of Elpistostege in natural habitat:
” This discovery pushes the origin of vertebrate fingers to the level of fish and tells us that the structure of the vertebrate hand was first developed deeply in evolution, just before the fish left the water. “
Elpistostegaliens: the links ensuring the transition fish-tetrapods
The evolution of fish into tetrapods – four-membered vertebrates to which humans belong – was one of the most important events in the history of life. The vertebrates were then able to leave the water and conquer the earth. One of the most important changes to complete this transition was the evolution of the hands and feet.
In order to understand the evolution of a fish fin into a tetrapod member, paleontologists study the fossils of lobed fin fish and tetrapods from the middle and upper Devonian (393-359 million years ago), called elpistostegaliens. These include the Canadian Arctic Tiktaalik, known only from incomplete specimens.
Comparison of the anatomy of the endoskeleton of the pectoral limbs (a) and the humerus (b) of tetrapod fish (Panderichthys, Tiktaalik and Elpistostege) and an early tetrapod (Tulerpeton). The red arrows indicate the ectepicondyle. Credits: Richard Cloutier et al. 2020
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According to Richard Cloutier of the University of Quebec, over the past decade, the fossils that have documented the fish-tetrapod transition have helped to better understand the anatomical transformations associated with breathing, hearing and food, as the habitat moved from water to land.
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” The origin of the fingers is linked to the development of the fish’s ability to support its weight in shallow waters or for short trips ashore. The increase in the number of small bones in the fin allows more flexibility to distribute its weight through the fin “
Elpistostege, the largest predator of Canadian surface water in the Devonian
The other characteristics that the study revealed relate to the structure of the bone of the upper arm or the humerus, which also shows characteristics that are shared with the first intermediate amphibians, between fish and tetrapods. Elpistostege was the largest predator living in shallow marine habitat in Quebec, about 380 million years ago.
It had powerful sharp fangs and could therefore have eaten several large lobed fin fish, found fossilized in the same deposits. Elpistostege was originally named after a small part of the skull structure, found in the fossil cliffs of Miguasha National Park, Quebec, and described in 1938 as belonging to one of the earliest tetrapods. Another part of the skull was found and described in 1985, demonstrating that it was really an advanced lobed fin fish. This complete copy of Elpistostege was discovered in 2010.
Sources: Nature
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