Though whether dignathans actually belong inside the acripod group is a lengthy semantic debate in and of itself, practically everyone agrees that the extant acripods are their closest relatives. Dignathans probably descended from a particular aquatic clade adapted to eating brachiopods and eurypterids. They might have found their forelimbs, practically useless in swimming, to be very helpful in crushing shells. Slowly, they moved closer and closer to their mouths, before they were fused as a second pair of jaws. Steering was now religated to the claspers entirely. Eodignathus is a wonderful example of an early fossil dignathan, being the oldest specimen found with arm-jaws. As these creatures grew larger, some crocodile-like forms began feeding on larger prey, such as latapods, whose bony shells were no match for their pair of destructive jaws. Eodignathus, however, was just a small benthic durophage, feeding on mostly brachiopods and bivalves.
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