Amphibians first appeared on Earth during the Devonian period, which was more than 400 million years ago. While this period is most famous for producing an abundance of fish, it also gave rise to the transition between fish and amphibians. It was during the Carboniferous period that amphibians flourished.
A fossil found in the Canadian Arctic in 2004 revealed that there were creatures that had vertebrae, as well as fins, that allowed them to move through water. The fossil also included a snout for breathing using air, as well as ribs and a neck. During this time, amphibians spent most of their time in water, but featured simple lungs and skin that allowed them to breathe on land.
During the Carboniferous period of 299 to 360 million years ago, amphibians evolved significantly. As the land became more arid there was a need to use amniotic eggs for production, causing amphibians to evolve into a more land-suitable form. During this time, amphibians evolved to have stronger structures, large flat heads and short limbs. Their skulls became deeper and their bodies were sprawling, which allowed them to move around with ease. At this point there were early examples of crocodiles, lizards and snakes, as well as early signs of synapsids.