Question

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

Answer 1

Hint: Jaw suspension refers to the connection of upper and lower jaw. This relation is to be appropriate to allow the basic mastication function. This suspension varies in various life forms.

Complete answer:
Jaw suspension refers to the attachment of the lower jaw to the upper jaw or skull. This initiates biting and chewing. These attachments can be variable depending upon the modifications in the vertebral arches. It is seen in vertebrates.

Option A— Amphistylic—It is present in primitive elasmobranchs. The jaws are made up of cartilage. Modification is not seen in such organisms. In these organisms the upper jaw is made up of pterygoqodrate and the lower is made up of meckel's cartilage. There is no change in hyoid arch. The lower cartilage attaches to the upper pterygoqodrate and hyoid arch.

Option B— Craniostylic — This type is seen in mammals. In mammals the pterygoqodrate transforms into incus and alisphenoid. Meckle’s cartilage transforms into malleus. This is not available to act as jaw suspension hence it directly attaches to the skull i.e known as squamosal. This type can also be seen in monotremes.

Option C— Autostylic— In this modification the pterygoqodrate transforms into epipterygoid and quadrate. Quatrate is the one which connects with the lower jaw. The second arch i.e hyomandibular gets transformed into columella bone. This does not act as suspension.

Option D— Hyostylic— This is seen in modern sharks. The lower jaw attaches to pterygoqodrate. Pterygoqodrate attaches to the hyomandibular cartilage.

So, the correct answer is B.

Note: Jaw suspension can be — amphistylic, autodiastylic, hyostylic, autostylic, monostylic, streptostylic, craniostylic and holostylic. In the case of mammals it is craniostylic. This jaw suspension is essential for biting and chewing of the food.