Question

Jaw suspension of mammals is
A. Amphistylic
B. Autodiastylic
C. Hyostylic
D. Craniostylic

Answer 1

Hint: Jaw suspension implies attachment of the lower jaw to the upper jaw or to the skull for productive biting and chewing. There are various ways in which these attachments are achieved, based on the variations in the visceral arches in the vertebrates.

Complete Answer:
For successful chewing, jaw suspension means the merger of the upper jaw and lower jaw or skull. Humans and all other animals that are warm-blooded vertebrates with hair include mammals. They feed their young with milk and have a brain that's more well-developed than most animal forms.
- Amphistylic: It is a form of jaw suspension seen in some sharks. Their upper jaw is positioned against the cranium and the hyomandibular is also supported. There is no modification of visceral arches in primitive elasmobranchs and they are made of cartilage.
- Autodiastylic: The skull is attached to the upper jaw and the lower jaw is attached directly to the upper jaw. The branchial arch is the second arch which does not engage in jaw suspension.
- Hyostylic: A type of jaw suspension seen in most fishes that do not clearly attach the upper jaw to the cranium. A ligament at the front end and the hyomandibular at the rear end form the attachment between the cranium and upper jaw.
- Craniostylic: Mammals have only a single paired dental bone in their lower jaw. In most vertebrates, the articular and quadrate bones are jaw joints but are relocated in mammals to the ear. In the braincase, the entire upper jaw is incorporated and the suspension of the jaw is Craniostylic.

So, the correct answer is Option D, Craniostylic.

Note: Craniostylic jaw suspension is a variation of the autostylic suspension. The lower jaw is closely attached to the so-called squamosal skull bone. Meckel's cartilage is turned into malleus, so suspension of the jaw is not usable.