The first four-legged fins turned into paws during the development of land

Changes in the shape of the humerus played an important role in the adaptation of the ancestors of tetrapods to life on

dry land. Accordingly, by studying the evolution of this part of the skeleton, we can predict when our ancestors left the ocean. It turned out that this happened simultaneously with the appearance of limbs.

Stephanie Pearce, professor at Hardward University in the USA

In order to track changes in the structureorganisms of extinct tetrapods, a group of researchers made 40 three-dimensional models of fossil humerus bones, their representatives were just participants in this turning point in development.

The first true amphibians, which could live on land almost permanently, appeared approximately 20-30 million years after these fish left the ocean.

The humerus bone attaches the front leg to the body,it also contains many muscles and must withstand a lot of stress during limb movements. Therefore, the bone contains a large amount of important functional information related to the movement of the animal.

Researchers have suggested that evolutionaryChanges in the shape of the humerus, from short and squat in fish to more elongated and characteristic of tetrapods, had important consequences associated with the transition to a terrestrial lifestyle.

As a result of the analysis, the researchers found thatthe humerus of the first amphibians, such as acanthostega or ichthyostega, were already adapted for life on land, despite the fact that many paleontologists believed that these animals differed little in their way of life from modern lobe-finned fish.

In the near future, Pierce and her colleagues wantcheck out these alternative theories. They plan to study how the shape of some other bones of the oldest amphibians and the last lobe-finned fish changed. For example, scientists want to check if the front and hind legs appeared at the same time.

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