Many temnospondyls are much larger than living amphibians , and superficially resemble crocodiles . Others are smaller and resemble salamanders . Most have broad , flat heads that are either blunt ( brevirostrine ) or elongated ( longirostrine ) . The skulls are rounded or triangular in shape when viewed from above , and are usually covered in pits and ridges . The rugged surfaces of bones may have supported blood vessels , which could transfer carbon dioxide to the bones to neutralize acidic build up in the blood ( early semiaquatic tetrapods would have had difficulty expelling carbon dioxide from their bodies while on land , and these dermal bones may have been an early solution to the problem ) . Many temnospondyls also have canal @-@ like grooves in their skulls called sensory sulci . The sulci , which usually run around the nostrils and eye sockets , are part of a lateral line system used to detect vibrations in water . As semiaquatic animals , most temnospondyls have small limbs with four toes on each front foot and five on each hind foot . Terrestrial temnospondyls have larger , thicker limbs , and some even have claws . One unusual terrestrial temnospondyl , Fayella , has relatively long limbs for its body , and probably lived as an active runner able to chase prey .