Very little is known of the soft tissue of temnospondyls . A block of sandstone , described in 2007 from the Early Carboniferous Mauch Chunk Formation of Pennsylvania , included impressions of the bodies of three temnospondyls . These impressions show , when alive , they had smooth skin , robust limbs with webbed feet , and a ridge of skin on their undersides . Trackways referable to small temnospondyls have also been found in Carboniferous and Permian rocks . The trackways , called batrachichni , are usually found in strata deposited around freshwater environments , suggesting the animals had some ties to the water .