Jaw suspension of mammals

A. Amphistylic

B. Craniostylic

C. Autostylic

D. Hyostylic

Jaw suspension refers to the way the lower jaw is attached to the upper jaw or skull, enabling biting and chewing. The type of attachment varies among vertebrates due to modifications in the vertebral arches.

Option A – Amphistylic

• Found in primitive elasmobranchs (early sharks).
• The jaws are cartilaginous, with the upper jaw formed by the pterygoquadrate and the lower by Meckel’s cartilage.
• The hyoid arch remains unchanged.
• The lower cartilage attaches both to the pterygoquadrate (upper jaw) and the hyoid arch.

Option B – Craniostylic

• Seen in mammals.
• The pterygoquadrate evolves into the incus and alisphenoid, while Meckel’s cartilage becomes the malleus.
• Since these structures no longer function in jaw suspension, the lower jaw attaches directly to the skull via the squamosal bone.
• This type is also found in monotremes.

Option C – Autostylic

• The pterygoquadrate transforms into the epipterygoid and quadrate, with the quadrate articulating with the lower jaw.
• The second arch, the hyomandibular, evolves into the columella bone, which does not aid in suspension.

Option D – Hyostylic

• Characteristic of modern sharks.
• The lower jaw attaches to the pterygoquadrate, which in turn is supported by the hyomandibular cartilage.

So, the correct answer is B.