The evolution of limbs with functional toes from fish fins took place about 400 million years ago in the Devonian. This morphological transition allowed vertebrates to leave the water to conquer the land and gave rise to all four-legged animals – an evolutionary lineage that includes all amphibians, reptiles, birds, and mammals (including humans). Scientists decided to find out at what stage in the development of fish this happened. The team’s research is published in the latest issue of Science Advances.
Since the 19th century, several theories have been put forward, based on both fossils and embryos, in an attempt to explain how this transformation took place. However, how exactly the hands and fingers evolved from the fins of the fish remained unknown.
An international team of biologists has identified how limbs evolved from fins using the embryos of an Australian lungfish (Neoceratodus forsteri) to study them. The Australian lungfish is the closest living relative of quadrupeds and is often considered a “living fossil” because it still resembles fish that lived when the first tetrapod vertebrates began to walk on land. For these reasons, the fins of lungfish provide a better guideline for studying the evolutionary transition of fins to limbs than any other species of fish in existence.
Research by a team of biologists shows that a primitive hand is present in the fins of lungfish, but at the same time suggests that the unique anatomy of the limbs with fingers evolved only during the emergence of tetrapods through changes in the embryonic state.
In the future, in order to fully understand what makes our limbs so different from fish fins, the researchers plan to conduct further analysis of fin and limb development using lung-breathing, as well as more modern fish species such as cichlids whose embryos are easier to examine with CRISPR.