Evolution: Upper arm may hold the key to how vertebrates rose from the seas 390 million years ago - Daily Mail

The key to how vertebrates first rose up out of the ocean and began to conquer the land some 390 million years ago may lie in the upper arm bone, a study has found. .

US and UK experts found that the development of the humerus — the bone that runs from the shoulder to the elbow — made the animals better walkers than swimmers.

This developed led to the emergence of the tetrapods — four-legged animals that, unlike their aquatic forebears — mostly lived on the land.

It triggered the emergence of tetrapods — four-legged animals that mostly live on land.

This developed led to the emergence of the tetrapods (pictured) — four-legged animals that, unlike their aquatic forebears — mostly lived on the land.

The humerus is invaluable for movement because it hosts key muscles that absorb much of the stress generated by quadrupedal — that is, 'four-legged' — locomotion.

The analysis covered the transition from aquatic fishes to terrestrial tetrapods — including an intermediate type with previously unknown locomotor capabilities.

The researchers found that the emergence of limbs in this latter group coincided with the transition onto land — but that these pioneers were not great at walking.

The analysis covered the transition from aquatic fishes (left) to terrestrial tetrapods (right) — including an intermediate type (middle) with previously unknown locomotor capabilities

The researchers found that the emergence of limbs in this latter group coincided with the transition onto land — but that these pioneers were not great at walking