694 



COLLEGE ZOOLOGY 



MARSU 



\ 



U PIALIA | 



,'MODERN BIRDS N , 



MAMMALIA! / 



/- -i 



\ MONOTREMATA /SERPENTES , TOOTH 

 V ^ 5" \ 



ED BIRDS 



SALI ENTlV-TESTUDI N ATA 



SQXJAMATA 

 THEROMORPHA 



SMOHRANCHII 



FIG. 551. Phylogenetic tree of vertebrates. Double underscoring in- 

 dicates an extinct group; single underscoring, those that have but a few 

 living representatives. The boundaries of the classes are represented by 

 dotted lines. (Modified after Wilder.) 



