Sauropsid
Between the lobe-finned fish tetrapods and the first amphibia and amniotes in the Middle Carboniferous lies a gap of 30 million years, with few satisfactory tetrapod fossils. This is "Romer's gap". Some new fossils were found in the 1990s, such as Pederpes, right in the middle of the Romer Gap. The gap still obscures the details of the tetrapod transition.