squamosoids 



nasal 



lermohyal 



maxilla 



retroarticular 



entosplenial 

 ostegal ray supramoxilla 



Bsupraongular' 



angula 

 retroarticular 

 quadratojugol 



ranchiostegal roy 

 interopercle 

 preopercle 



supratemporotobular 

 intertemporal 



position of pineal body 



supratemporotobular 

 intertemporal \ 



lacrimal series 

 lateral rostral 

 medial rostral 



medial rostral 



lateral rostral 

 extroscapulor series lacrimal 



postparietol 

 extroscapulor series 



premaxillo 



vo^ier palatine 



pterygoid ectopterygoid 



ectopterygoid 



metapterygoid 



Figure 5-14. Semidiagrammatic sketches comparing the head skeletons of Upisosteus, to the left, 

 and Amio, on right. A and B, lateral views of heads,- C and D, dorsal views of heads; E and F, palatal 



that group; not including it fails to recognize the great 

 variation known to occur in that group. 



Relationship with the choanafes A relationship between the 

 actinopterygians and the choanates can be based on the 

 similarities of the head skeletons. Until quite recently, such 

 comparisons were used to demonstrate the common pattern 

 of bones in the Osteichthyes. Goodrich remarked that the 

 similarity of roof patterns was one of the strongest pieces of 

 evidence of common ancestry. Westoll pointed out that the 



parietal fenestra, and several other landmarks of the cra- 

 nium, had fixed relationships and that what had been called 

 the frontal in the crossoptcrygian fish was the homolog of the 

 amphibian parietal. Westoll rearranged the names of the 

 bones of the crossoptcrygian to agree with those of the am- 

 phibian but assumed that the bones of the actinopterygian, 

 which had been homologized with those of the crossopte- 

 rygian, were so different as not to be comparable. 



The problem of the origin of the roof pattern is one on 

 which there has been much discussion but little agreement. 



GNATHOSTOME FISHES • 117 



