This order includes only the extinct bird, the Archaeopteryx macrura (fig. 351), a single specimen of which - and that but a fragmentary one - has been discovered in the Lithographic Slates of Solenhofen (Upper Oolites). This extraordinary bird appears to have been about as big as a Rook; but it differs from all known birds in having two free claws belonging to the wing, and in having a long lizard-like tail, longer than the body, and composed of separate vertebrae. The tail was destitute of any ploughshare-bone, and each vertebra carried a single pair of quills. The metacarpal bones, also, were not anchylosed together as they are in all other known birds, living or extinct, and two of the digits appear to have been unguiculate.

The sub-class Saurornithes includes only the single order Saururae, of which no other representative is known than the

Fig. 351.   Archaeopteryx macrura, showing tail and tail feathers, with detached bones.

Fig. 351. - Archaeopteryx macrura, showing tail and tail-feathers, with detached bones.

Jurassic Archaeopteryx. From the presence of feathers it may be inferred that Archaeopteryx was hot-blooded, and this character, taken along with the structure of the extremities, is sufficient to justify the reference of this unique fossil to the Birds. In the long lizard-like tail, composed of numerous free vertebrae, each of which bears a pair of tail-feathers, in the fact that the metacarpals were not anchylosed together, and in the possession of two free clawed digits to the manus, Archaeopteryx differs from all other known birds, living or extinct. There is also some reason to believe that the jaws were furnished with teeth sunk in distinct sockets.

Sub-class IV. Odontornithes.