The Tlieory of Evolution 41 



the anatomical evidence alone, that the progression had been 

 in some such order as the geological record shows. The 

 limitation referred to above is this : that while the mammals 

 arose later than the birds, we need not suppose that the 

 mammals arose from the birds, and not even perhaps from 

 the reptiles, or at least not from reptiles like those living 

 at the present day. The mammals may in fact, as some 

 anatomists believe, have come direct from amphibian-like 

 forms. If this is the case, we find the amphibians giving rise 

 on one hand to reptiles and these to birds, and on the other 

 hand to mammals. 



This case illustrates how careful we should be in interpret- 

 ing the record, since two or more separate branches or orders 

 may arise independently from the same lower group. If the 

 mammals arose from the amphibians later than did the rep- 

 tiles, it would be easy to make the mistake, if the record was 

 incomplete at this stage, of supposing that the mammals had 

 come directly from the reptiles. 



That the birds arose as an offshoot from reptile-like forms 

 is not only probable on anatomical grounds, but the geo- 

 logical record has furnished us with forms like archasop- 

 teryx, which in many ways appears to stand midway between 

 the reptiles and birds. This fossil, archseopteryx, has a bird- 

 like form with feathered wings, and at the same time has a 

 beak with reptilian teeth, and a long, feathered tail with a 

 core of vertebrae. 



From another point of view we see how difficult may be 

 the interpretation of the geological record, when we recall 

 that throughout the entire period of evolution of the verte- 

 brates the fishes, amphibians, reptiles, and birds remained still 

 in existence, although they, or some of them, may have at 

 one time given origin to new forms. In fact, all these groups 

 are alive and in a flourishing condition at the present time. 

 The fact illustrates another point of importance, namely, that 

 we must not infer that because a group gives rise to a higher 



