Life on Earth - Episode 06 - The Swarming Hordes

"The sixth episode describes the move from water to land. The fish that did so may have been forced to because of drought, or chose to in search of food. Either way, they eventually evolved into amphibians. Such creatures needed two things: limbs for mobility and lungs to breathe. The coelacanth is shown as a fish with bony fins that could have developed into legs, and the lungfish is able to absorb gaseous oxygen. However, evidence of an animal that possessed both is presented in the 450 million-year-old fossilised remains of a fish called a eusthenoptron. Three groups of amphibians are explored. The sicilians have abandoned legs altogether to aid burrowing, newts and salamanders need to return to the water to allow their skins to breathe, but it is frogs and toads that have been the most successful. Attenborough handles a goliath frog, the largest of the species, to demonstrate its characteristics. Their webbed feet form parachutes that turn them into "dazzling athletes", and some can leap over 15 metres — 100 times their body length. In addition, their vocal sacs ensure that mating calls can be heard from up to a mile away. Poison dart frogs deter predators by means of venom, and one such example could kill a human. Various methods of breeding are examined, including laying eggs in rivers, depositing them in other damp habitats for safety or, as with the Brazilian pipa, embedding them within the skin of the parent itself."