jaw evolution

Question 1

chondrichthyans jaw

Answer 1

Palatoquadrate = cartilaginous upper jaw, Meckel’s cartilage = cartilaginous lower jaw

Functional Elements: Meckel’s cartilage forms the main framework of the lower jaw, bearing teeth, while the upper jaw consists of the palatoquadrate, also bearing teeth.
Cranial Skeleton Division: These functional elements are derived from the chondrocranium, the cartilaginous part of the skull.

Question 2

Actinopterygians

Answer 2

Palatoquadrate bone = upper jaw, Dentary bone = lower jaw
Bony fishes partially or fully ossify these elements for enhanced structural support.

Question 3

Amniotes

Answer 3

Upper Jaw: Palatoquadrate bone (in reptiles and birds) or Incus bone (in mammals)
Lower Jaw: Articular and quadrate bones (in reptiles and birds) or Dentary bone (in mammals).

Question 4

Mammals

Answer 4

Maxilla and premaxilla bones = upper jaw, Dentary bone = lower jaw