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Our ancestors' transition out of the water and onto the land was a pivotal moment in evolution. No longer buoyed by water, early tetrapods (animals with four limbs) had to overcome gravity in order to move their bodies. Exactly how those early pioneers first evolved the fundamental capacity to walk has fascinated scientists for many years.
Fossil discoveries can tell us how and when vertebrates evolved the physical features needed to move onto land. But new research published in the journal Cell suggests that the neural circuitry needed to walk probably existed long before actual legs evolved. Because land-based animals and fish share the same circuitry today, their last common ancestor—an ancient fish which existed 420m years ago—probably also had that circuitry and used it to move around beneath the water.
Idea - Tetrapods - Fossil - Record - Documents
We already have a reasonably good idea of when fish evolved into land-based tetrapods because the fossil record documents the sequence of changes to their bodies. One of the most iconic specimens is Tiktaalik, a "transitional" fossil dating to around 375m years ago.
Tiktaalik is special, because though it retains many fish-like characteristics, it also possesses wrist bones, suggesting that it could support itself on its front limbs. Fossils from rocks older than Tiktaalik lack these wrist bones, and are generally more fish-like. Fossils from younger rocks include more tetrapod-like species, with distinct digits and limbs.
Research - New - York - University - US
But the new research from New York University in the US suggests that fish needed more than just legs to learn how to walk, and in fact evolved the neural circuitry involved much earlier on. The researchers reached this conclusion by studying little skates, fish that move along the ocean floor by moving their hind fins in a left-right pattern, much as we would move our legs when walking.
The researchers found that the neural circuits little skates...
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