THE JURASSIC PERIOD 235 



its distinctive Bird-characters of feet, limb-bones, beak, and es- 

 pecially of feathered wings, it had the long tail and toothed jaws 

 (see Fig. 147) of a Reptile. The structure of the tail is especially 

 significant. In ordinary Birds the tail proper is shortened up to a 

 rudiment and ends in a large bone, from which radiate the feathers 

 of the tail-fan. In this earliest Bird, on the contrary, the tail proper 

 is as long as all the rest of the vertebral column put together, 

 consisting, as seen in the figure, of twenty-one joints from which the 

 fan feathers come off in pairs on each side. The tail-fan of this 

 Bird differs from that of typical Birds precisely as the tail-fin of 

 the earliest Fishes differs from that of typical Fishes. The tail-fan 

 of this earliest Bird, like the tail-fin of the earliest Fishes, was 

 vertebrated. This wonderful reptilian Bird was called Archeop- 

 teryx ('primordial winged creature'), and the species macrura 

 ('long-tailed'). ... So complete is the mixture of the two kinds 

 of characters that some zoologists believe that the reptilian char- 

 acters predominate, and that it should be called a Bird-like Reptile. 

 Most agree, however, that it is a reptilian Bird." * Thus, while 

 the evidence seems conclusive that Birds were evolved from Rep- 

 tiles, there is no conclusive evidence that they were derived from 

 the flying Reptiles (Pterosaurs). Rather there appears to have 

 been a development of these two remarkable groups of flying 

 creatures alongside each other. 



Mammals. — This important class, first known from the Tri- 

 assic, continued to be represented by only comparatively few 

 small, very primitive forms in the Jurassic. The scant records 

 show these creatures to have been no larger than Mice or Rats 

 and low in organization (i.e. Monotremes or Marsupials). As 

 already stated, Mammals remained very subordinate throughout 

 the Mesozoic era. 



1 J. LeConte: Elements of Geology, Ed., pp. 462-463. 



