In 2012, Jennifer Clack, one of the most famous vertebrate paleontologists of the modern era, concluded, “The question of where tetrapods evolved is even more difficult to answer than that of when.”
Echoing this frustration, a 2018 research paper stated, “The fish-to-tetrapod transition is one of the fundamental problems in evolutionary biology.”
The alleged fins-to-feet evolutionary transformation is thought to have brewed during the deposition of Devonian strata, ....the geological period known as the Age of the Fishes—a point in the rock record when numerous types of unique fish show up suddenly with no evolutionary precursors.
The supposed transition from water to land would have required the
Anatomically speaking, specialized appendages and skeletons along with associated musculatures would need to have formed to support a creature’s body weight against gravitational forces to allow it to move on land. In contrast, fish are highly specialized to live buoyantly in the water, largely avoiding the effects of gravity on movement.
---Furthermore, to facilitate respiration, gill breathing would have needed to transform into lung breathing—a radical physiological change in itself—through other highly specialized innovations.
After Ichthyostega, any other transitional form candidates simply disappear in the rock record, as noted by Clack: “The fossil record of post-Devonian tetrapods is notoriously sparse for about 30 million years after the Devonian/Carboniferous (Mississippian system) boundary.” Clack also states, “The origin of limbed tetrapods did not coincide with the acquisition of full terrestriality, an outcome that probably arose in the Early Carboniferous. This latter part of the story is documented by few fossils.”
In other words, the huge evolutionary gap between water and land still exists with no fossil solution in sight."