Origin and Evolution of Life — BIOLOGY STD 12 Science — Question

(1) Archaeopteryx shows reptilian as well as avian characters.

(2) Reptilian characters are as follows:

• Jaws with homodont (all similar) teeth. Bones are nonpneumatic i.e. solid.
• Ribs have a single head. Sternum without keel.
• Abdominal ribs present which are like the crocodilian ribs.
• Forearms have three digits ending in distinct claws while the hind limb has four digits ending in clawed digits.

(3) Avian characters shown by it are as follows:

• Forearms modified into wings.
• Feathery exoskeleton.
• Skull bones are completely fused.
• Cranium is rounded with large orbits and a single condyle.
• Jaws are modified into beak.
• Limb bones have first toe in opposable manner. Foot present with clawed digits. Since it showed characters of both the classes, it is considered as the connecting link between the two.