[3] Many of these species were also the first to develop adaptations suited to terrestrial over aquatic life, such as neck mobility, more robust lungs and hindlimb locomotion.
The late Devonian vertebrate transition was preceded by terrestrial invasion by fungi, land plants and invertebrates such as arthropods.
[5] Lungfish appeared approximately 400 million years ago, enduring rapid evolution during the Devonian era, which became known as the dipnoan renaissance.
The Acanthostega species, known as the fish with legs, is considered a tetrapod by structural findings but is postulated to have perhaps never left the aquatic environment.
Pederpes, Westlothiana, Protogyrinus, and Crassigyrinus descended from these species into the Early Carboniferous period and were the first land vertebrates, indicating the crown group originated and split in that time, around 350 Ma.
[5] A theory put forth by Joseph Barrell possibly helps explain what may have initiated these push factors to become relevant in the late Devonian.
The extensive oxidized sediments that were present in Europe and North America (since they lived in Euramerica) during the late Devonian are evidence of severe droughts during this time.
These droughts would cause small ponds and lakes to dry out, forcing certain aquatic organisms to move on land to find other bodies of water.
These were largely the niches and opportunities that were available for exploitation in the terrestrial environment, and include higher environmental oxygen partial pressures, favourable temperatures, and the lack of competitors and predators on land.
These challenges allowed for rapid natural selection and niche domination, resulting in an adaptive radiation that produced many different vertebrate land species in a relatively short period of time.
The stressors of the musculoskeletal system are different in air than they are in water, and the muscles and bones must be strong enough to withstand the increased effects of gravity on land.
[4] The ancestral species of tetrapods that lived entirely in water had tall and narrow skulls with eyes facing sideways and forwards to maximize visibility for predators and prey in the aquatic environment.
As the ancestors of early tetrapods started inhabiting shallower waters, these species had flatter skulls with eyes at the tops of their heads, which made it possible to spot food above them.
As lineages moved from completely aquatic environments to shallower waters and land, they gradually evolved vertebral columns that increased neck mobility.
They lost the lateral line system, a network of canals along the skull and jaw that are sensitive to vibration, which does not work outside of an aquatic environment.
These pre-adaptations have allowed vertebrates to venture onto land hundreds of times, but were not able to accomplish the same degree of prolific radiation into diverse terrestrial species.