The Rise of the Mammals 



out by one of the many volcanoes characteristic 

 of the period. These shales contain vast num- 

 bers of insects, and have yielded many thou- 

 sand specimens and many hundred species, 

 this being one of the most famous localities in 

 the world for fossil insects. 



Very little can be said of the birds of this 

 period, for while fragments of several waders 

 have been found, but two birds are at all well 

 known. One of these, Palceospiza helli^ was 

 described as a sparrow ; the other was not at all 

 unlike the small curassow living in Texas, 

 known as the chachalaca.* A bird as heavy 

 as an ostrich is indicated by some fragments of 

 a leg-bone from New Mexico, but there is rea- 

 son to suppose that in spite of its size it was 

 not a relative of that bird. Its real affinities 

 are very likely with a group of huge birds 

 whose remains are found in Miocene strata of 

 Patagonia. It is to be noted that birds have 

 made rapid progress since the Cretaceous, for 



* This is one of the instances where the scientific name is cer- 

 tainly no harder than the common name. Ortalis vetula is easier 

 to pronounce than chachalaca, and conveys just as good an idea 

 of the bird to the average person. 



16 233 



