 Most aquatic <unk> 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 <unk> <unk> is well known , and is one of the most highly adapted . <unk> is thought to have lifted its skull to around 50 ° above horizontal through the <unk> of the <unk> @-@ <unk> joint between the <unk> <unk> of the skull and the <unk> <unk> of the neck . As the skull is raised , the <unk> bone pushes forward and causes the lower jaw to <unk> outward . Other <unk> probably also lifted their skulls , but they are not as well adapted for such movement . <unk> Watson was the first to suggest skull lifting as a means of feeding in <unk> . He envisioned that <unk> , a much larger <unk> than <unk> , was able to make the same movement . <unk> <unk> <unk> also supported the idea in 1959 , suggesting that <unk> also fed in this way . At the time it was thought that these <unk> 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 <unk> . <unk> , a close relative of <unk> , also has a <unk> skeleton that muscles may have attached to . <unk> has very small teeth and a large area for muscle attachment behind the skull , suggesting that it could <unk> feed by rapidly opening its mouth . 
