COLLETTE and CHAO: SYSTEMATICS AND MORPHOLOGY OF THE BONITOS (SARDINI) 



SPHENOTIC 



PTEROSPHENOID 

 FRONTAL 

 LATERAL ETHMOID 



PTEROTIC 



VOMER 



ETHMOID 



INTERCALAR 

 EXOCCIPITAL 

 BASIOCCIPITAL 



FIRST VERTEBRA 



FRONTAL 



PARASPHENOID 



BASISPHENOID 



PROOTIC 



Figure 17.-Ventral view of skull of Gymnosarda unicolor, Truk Islands, 6% mm FL. 



where the upper shelf meets the pterotic and the 

 lower shelf meets the sphenotic. The frontal crest 

 is absent in Allothunnus (Figure 24), indistinct in 

 Cybiosarda, Orcynopsis, and Gymnosarda 

 (Figures 20-22), and is most prominent in the 

 species of Sarda (Figure 23). 



Basisphenoid.-The basisphenoid is a Y-shaped 

 bone, connected dorsally to the prootics and the 

 pterosphenoids. In anterior view, the basisphenoid 

 bisects the entrance of the myodome, with an 

 anteriorly and a posteriorly directed process in its 

 upper half (Figures 20-24), except in Allothunnus 

 (Figure 25). Ventrally, the basisphenoid extends 

 toward the parasphenoid to which it is connected 

 in all the bonitos except Allothunnus. 



Godsil (1954) studied possible differences 

 between the basisphenoids of eastern Pacific Sar- 

 da chiliensis and S. orientalis. He concluded that 

 the lower portion of the basisphenoid in S. 

 chiliensis is generally a narrow bone, only slightly 



expanded, and firmly ankylosed to the 

 parasphenoid. In S. orientalis, the lower extremity 

 of the basisphenoid is greatly expanded and it is 

 apparently only loosely attached to the 

 parasphenoid. We agree with his statements in 

 part. In S. orientalis from the eastern Pacific and 

 the Indo-West Pacific, the lower extremities of the 

 basisphenoid are expanded and firmly attached to 

 the parasphenoid. In northeast and southeast 

 populations of 5. chiliensis, the lower portions of 

 the basisphenoid are narrow or slightly expanded 

 and are either firmly or loosely ankylosed to the 

 parasphenoid. In general, the lower extremities of 

 the basisphenoid in S. chiliensis are less expanded 

 and less firmly attached to the parasphenoid than 

 in S. orientalis. 



The angle of the long axis of the basisphenoid 

 relative to the parasphenoid in bonitos is less 

 variable than in Thunnus (Gibbs and Collette 

 1967), but no specific differences were found 

 among the bonitos, except in Allothunnus. The 



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