Archaeopteryx is a connecting link (missing link) between reptiles and birds. The following are the reptilian and avian characters of Archaeopteryx.
Reptilian characters:
1. Jaws are provided with homodont teeth.
2. Long, lizard like tail with 20 free caudal vertebrae.
3. Bones are not pneumatic.
4. Cervical vertebrae are fewer, 9 to 19.
5. Amphicoelus vertebrae as in Sphenodon.
6. Cervical and abdominal ribs are present, in addition to thoracic ribs; Ribs are single-headed and without uncinate process
7. Sternum is weak or absent.
8.Eyes are provided with sclerotic ossicles.
9. Scales are present.
10. Forelimbs are provided with threw free fingers tipped with claws. The phalangial formula is 2, 3, and 4 in the I, II, and III fingers.
11. Carpals and metacarpals are free; there is no carpometacarpus.
12.Pelvic girdle has an elongated ilium and a backwardly directed pubis.
Avian Characters:
1. Presence of feathers. If the feathers of Archaeopteryx were not preserved in the fossil. It would have been taken for some bipedal diapsid reptile.
2. Forelimbs are modified as wings.
3.Tail bears modified as wings.
4.Tail bears two rows of feathers.
5. Rounded braincase
6. Beaks are present.
7. Bones in the skull are intimately fused.
8. Bones of limbs and girdles are bird-like.
9. A keel is present in the sternum.
10.Tibia and fibula are separate.
11. V-shaped furcula is present.