268 . ORDEES OF BIRDS. 



The sub-class Saurornithes includes only the single order 

 Saururm, of which no other representative is known than the 

 Jurassic Arcliccopteryx. From the presence of feathers it 

 may be inferred that Archmopteryx 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 numer- 

 ous 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, 

 Archceopteryx 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. Odontoenithes, 



Ordee I. Odontolc^e. — This order has been founded by 

 Marsh for the reception of the extraordinary Hcspcrornis 

 regalis, from the Cretaceous rocks of North America. In 

 this wonderful fossil we have a gigantic diving-bird some- 

 what resembling the true " Divers " or " Loons " {Colymhus), 

 but having the jaws furnished with numerous conical re- 

 curved teeth, sunk in a deep continuous groove (fig. 592, & 

 and (7). 



The front of the upper jaw does not carry teeth, and was 

 probably encased in a horny beak. The breast -bone is 

 entirely destitute of a central ridge or keel, and the wings 

 are minute and quite rudimentary ; so that Hesperornis, 

 unlike Ichthyornis, must have been wholly deprived of the 

 power of flight, in this respect approaching the existing 

 Penguins. The tail consists of about twelve vertebrae, of 

 which the last three or four are amalgamated to form a flat 

 terminal mass, there beino- at the same time clear indications 

 that the tail was capable of up and down movement in a 

 vertical plane, this probably fitting it to serve as a swimming- 

 paddle or rudder. The vertebra of the cervical and dorsal 

 regions are of the ordinary ornithic type. The legs were 

 powerfully constructed, and the feet were adapted to assist 

 the bird in rapid motion through the water. The known 



