OSTRACODERMS 



CHONDRICHTHYES 



PRIMITIVE 

 CHORDATE 

 Gills for 

 filter- 

 feeding 



Restriction of 

 ■gill slits : 

 mouth 



supported by 

 2nd. visceral 

 arch 



ACTINOPTERYGII 

 development 

 of operculum 



CHOANICHTHYES 

 internal nostrils 



CROSSOPTERYGII 



ANCESTRAL 

 TETRAPODS 



DIAPSIDS 

 conus split into 3] 

 carotids off 

 right systemic 



STEM 

 REPTILES 

 costal pump 



-5YNAPSIDS- 

 Ca rot ids off 

 left systemic 



Phylogenetic tree showing the major respiratory 

 and the relationships of the groups that 



