Giant amphibious Mastodonsaurus lived on Earth in the middle Triassic about 230 million years ago. These distant relatives of frogs lived in large ponds with fresh water and were passive predators. They mostly waited for their prey hiding near the bottom and becoming a sort of a live trap. In Russia their fossil remains were discovered in Southern Ural. The species was described in 1955 by paleontologist E.D. Konzhukova.

Modern amphibians as a rule are not so large; however there are exceptions, for example the Chinese and Japanese giant salamanders with a length of up to almost 1.5 m. The giant goliath frog can weigh almost 3 kilos.

Ancient amphibians could reach enormous proportions, up to 9 meters in length, so our five-meter long Paleopark inhabitant would not be the largest specimen. However large sizes did not much help ancient amphibians to win the competition with the first reptiles.