An article published in the journal “Cell” describes a research on the origin of the types of neurons needed to coordinate walking on the mainland. A team of researchers from the New York University School of Medicine focused in particular on the species little skate (Leucoraja erinacea), part of the most primitive vertebrate group, studying its neuromuscular and genetic development. The conclusion is that some fish started walking on the sea floor about 420 million years ago, about 20 million years before the early tetrapods started colonizing the mainland.