Question

Why is hyostylic jaw suspension NOT adaptive for tetrapods living on land?

Answer 1

Hyostylic jaw suspension involves the connection of both the jaws with skull through hyomandibular. The jaws are loosely bound and are connected to each other through hyoid arch. This type of jaw suspension is advantageous in providing a wide opening mouth for these organisms and hence makes it easier for them to capture and then take in a large sized prey. This also sometimes results in protrusing mouth and hence a wider gap is possible at time of predation.

In case of land dwelling tetrapods, the type of jaw suspension is autostylic which differs from hyostylic in having a modified hyomandibular cartilage which is involved in formation of columella or articular articulates or stapes and forms the part of middle ear in these organisms and plays a part in sound reception by them. This kind of feature were useless for water dwelling animals and so they preferred the hyostylic suspension which aided them in feeding. For land dwelling tetrapods, presence hyostylic jaw suspension would have left them without the development of middle ear because hyomandibular cartilage would have had its function in jaw articulation to the skull. In land dwellers the jaws are attached to the skull directly. This attachement prevents wide opening of the mouth and the movement of jaws is restricted in comparison to those with hyostylic suspension which is very flexible. This adaptation benefits the land dwellers by providing the sense of hearing in their ears along with being an organ for maintaining equilibrium in comparison to that of water dwelling bony fishes with the hyostylic jaw suspension.