426 



HISTORICAL GEOLOGY 



C 



complexity of the sutures 

 is concealed by the shell. 



such as is characteristic of the decline of many other animal 

 groups. Like their predecessors, they were ponderous and 

 clumsy in the extreme, and the small 

 size of the cavities in their skulls 

 shows how insignificant was the 

 capacity of their brains and how little 

 intelligence most of them possessed. 

 Externally they took on many pecu- 

 liar and apparently useless styles of 

 ornamentation, such as the great 

 bony plates and spines shown in 

 Figure 433. 



The coiled shells called ammonites 



FIG. 446. A Cretaceous , i , 



ammonite ornamented seem to have been ln the same sta S e 



with blunt spines. The of their career, and likewise exhibit 



many peculiar 



forms and or- 

 naments (Fig. 446). Some had spines, 

 others knobs or ridges, while some 

 showed a tendency to uncoil and re- 

 vert to the straight Orthoceras type, 

 although still keeping the highly 

 crumpled suture lines (Fig. 447). 



The birds in transition. The birds 

 in the Cretaceous period were far 

 more like our modern birds than was 

 the strange Archceopteryx of the Juras- 

 sic. In fact, the one characteristic 

 which linked them closely with that 

 ancestral form was the possession of 

 teeth resembling those of reptiles and 

 set in sockets or grooves in the jaws. 



That the birds had developed along Fm 447 . _ Fragment of 

 several widety divergent lines is shown a large partly uncoiled 



by the fact that Some which have ammonite, showing re- 



markable complexity of 



been, found in the Cretaceous rocks the suture lines. 



