Most aquatic stereospondyls have flattened heads . When feeding , they probably opened their mouths by lifting their skulls instead of lowering their lower jaws . The jaw mechanics of the plagiosaurid Gerrothorax is well known , and is one of the most highly adapted . Gerrothorax is thought to have lifted its skull to around 50 ° above horizontal through the flexing of the atlanto @-@ occipital joint between the occipital condyles of the skull and the atlas vertebra of the neck . As the skull is raised , the quadrate bone pushes forward and causes the lower jaw to protrude outward . Other stereospondyls probably also lifted their skulls , but they are not as well adapted for such movement . D.M.S. Watson was the first to suggest skull lifting as a means of feeding in temnospondyls . He envisioned that Mastodonsaurus , a much larger temnospondyl than Gerrothorax , was able to make the same movement . Paleontologist A.L. Panchen also supported the idea in 1959 , suggesting that Batrachosuchus also fed in this way . At the time it was thought that these temnospondyls lifted their heads with strong jaw muscles , but it is now thought that they used larger muscles in the neck that were attached to the large pectoral girdle . Plagiosuchus , a close relative of Gerrothorax , also has a hyobranchial skeleton that muscles may have attached to . Plagiosuchus has very small teeth and a large area for muscle attachment behind the skull , suggesting that it could suction feed by rapidly opening its mouth .