GREAT STEPS IN ORGANIC EVOLUTION 883 



cave or double-eggcup like, a form characteristic of fishes, rare above 

 that level among living animals, but by no means uncommon among 

 extinct reptiles. According to Marsh, "the brain of Ichthyornis was 

 extraordinarily small, and in its main features strongly reptihan", 

 e.g. in its elongated form and its prominent optic lobes. Its entire 

 bulk he estimated at less than a third of a tern's, while the largest 

 specimen that has been reconstructed must have stood about a foot 

 high. But the fact is that in spite of such well-marked reptilian 

 vestiges, even Ichthyornis does not help us far in our quest. For it 

 was already an indubitable Flying Bird or Carinate, i.e. in the same 

 sub-class as all Uving birds except the Flightless ostrich tribe 

 Ratitae. 



The oldest known fossil bird, Archseopteryx, is not only of the 

 highest interest in connection with our present problem, but affords 

 one of the clearest illustrations of what is meant by an "annectant 

 type" or "connecting link". So much so that some authorities 

 regard and class it, mistakenly we think, as a reptile, though most 

 others as a bird. The first specimen discovered in 1861 in the litho- 

 graphic stone quarries at Solenhofen in Bavaria was described by 

 Owen under the name Archceopteryx lithographica, and it is one of 

 the treasures of the British Museum. A better preserved specimen, 

 found in 1877 near Eichstatt in Bavaria, was described by Dames 

 and rests in the Berhn Museum. It is sometimes referred to a separate 

 genus, and called ArchcBornis siemensi. 



Archseopteryx was a bird about the bulk of a small hen, though of 

 very different build; yet we say "bird" emphatically, because it was 

 a "feathered biped". The marks of the feathers are clearly seen on 

 the fine-grained lithographic stone, and a notable peculiarity is the 

 arrangement of a single row on each side of the long and otherwise 

 lizard-like tail. 



Yet the creature swarmed with reptilian features. Thus the skuU 

 has more resemblance to that of some of the primitive reptiles called 

 Pseudosuchians than to that of modern birds. There are teeth in 

 both jaws, and there is no true "beak", that is to say, no great 

 elongation of the premaxillae, nor horny covering. 



The vertebrae were probably biconcave, as in various extinct 

 reptiles and in most fishes and a few reptiles to-day. There were at 

 least twenty vertebrae in the tail, in striking contrast to the very 

 short tail in all modern birds. For the long "tails" of pheasants and 

 the like are merely feather-tails, their true vertebral tail being 

 reduced and condensed as in ordinary birds. The ribs of Archae- 

 opteryx are not bird-like ; thus not showing the characteristic hooks 

 or "uncinate processes", which may, however, have been gristly 

 and therefore unpreserved in the fossil. But decidedly reptilian is 

 the presence of 9-12 pairs of ventral or abdominal ribs, interesting 

 structures not even hinted at in any living bird, but very well 



