LIFE IN SECONDARY TIMES 277 



or by some scourge operating in the regions in which they live. 

 Thus we must seek to discover what agency was capable of 

 destroying the most gigantic animals that ever dwelt on this 

 earth. 



From the beginning of the Secondary era two types of 

 Vertebrates had slowly and sparsely multiplied — Birds and 

 Mammals — which we have hardly had occasion to mention. 

 The oldest of the Birds, Archceopteryx lithographica, is known 

 by two forms only, discovered in the lithographic limestone of 

 Solenhofen of the Oolitic Period. Birds do not reappear 

 till four genera are found in the Chalk — Enaliornis of England, 

 Hesperornis, Ichthyomis, and Apatomis of Kansas, in North 

 America. All these Birds are still very strange. Archceop- 

 teryx had short jaws rounded at the end instead of being 

 pointed and elongated like those of the majority of present 

 Birds, and furnished with teeth. The anterior limbs had 

 wing-feathers, but the four toes terminating them were free 

 and provided with almost normal claws ; the tail was long and 

 reptilian and composed of twenty-two vertebra?, each bearing 

 a pair of long tail feathers — a most encumbering appendage 

 for flight, and had it not been for its feathers Archceopteryx 

 would undoubtedly have been classed among the Reptiles. 

 Thus is the reptilian origin of Birds clearty indicated. 



The Cretaceous forms had more distinct birdlike characters. 

 The beak was clearly characterized and the body ended in a 

 rump of normal form instead of in a long tail. Enaliornis and 

 Hesperornis had rudimentary wings, or none at all, and no keel 

 on the breast-bone. The vertebrae of Enaliornis were mostly 

 biconcave like those of the primitive Reptiles ; while those of 

 Hesperornis were concave on the terminal aspect, convex on the 

 other. In both these genera the teeth were situated in a simple 

 groove and not enclosed in alveoli, a fact that has led to their 

 classification together under the name Odontolcae. In Ichthyomis 

 and Apatomis the teeth were implanted in alveoli and accom- 

 panied by replacing teeth (Odontormae). The wings and the 

 keel on the breast-bone were well developed. It is evident that 

 these Birds, despite their alveolar teeth, were more primitive 

 than Hesperornis, whose wings had disappeared and whose 

 teeth, placed in a simple maxillary groove, were on the road to 

 disappearance. This fact alone would indicate that rumped 

 Birds were already old in the Cretaceous Period, seeing that 



