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



SPHENOTIC 



INTERCALAR 



FRONTAL 



LATERAL ETHMOID 



VOMER 



FIRST VERTEBRA 



ETHMOID 



EXOCCIPITAL 



PINEAL FORAMEN 



SUPRAOCCIPITAL 



EPIOTIC 



PARIETAL 



Figure ll.-Dorsal view of skull of Allothunniis fallai, California, 680 mm FL. X's indicate the points of attachment of 



intermuscular bones. 



In lateral view (Figures 20-24), bonito skulls are 

 similar to more advanced scombrids, but are more 

 elongate and have the roof of the orbit less fully 

 arched. Allothunnus (Figure 24) is most distinct in 

 having a more pointed anterior end and a deeper 

 posterior portion. The pterosphenoids project 

 ventrally from the roof of the skull and form a 

 partial interorbital septum which never fuses with 

 the parasphenoid as in large Thunnus thynnus 

 (see Gibbs and CoUette 1967). In the posterior part 

 of the orbit, the basisphenoid bisects the orbital 

 capsule by connecting the pterosphenoids and 

 prootic bones to the parasphenoid. The orbit is 

 formed by the posterior edge of the lateral eth- 

 moid, the ventral surface of the frontal and 

 pterosphenoid, the parasphenoid, basisphenoid, 

 and the anterior edge of the prootic. As expressed 

 by the ratio of orbit height to length (see section 

 on orbital region), the orbit is low and elongate in 

 bonitos (Table 4); Cybiosarda, Orcynopsis, and 

 Sarda have the lowest orbits as in Scomberomorus 

 and Acanthocybium. Gymnosarda and Allothun- 

 nus each have a more highly arched orbit 

 resembling that in Scomber, Grammatorcynus, 



Table 4. -Ratio of orbit height to length in species of Sardini. 



Rastrelliger, Auxis, Euthynnus, Katsuwonus, and 

 Thunnus (AUis 1903; Kishinouye 1923; Mago Lec- 

 cia 1958; Gibbs and Collette 1967; Gnanamuttu 

 1971). 



The posterior part of the base of the cranium is 

 formed by the lateral flanges of the parasphenoid 

 (ventral profile) and basioccipital (posterior 

 profile). Along the dorsal profile, a crest formed 

 anteriorly by the joint between the frontals is 

 most distinctive in Sarda, as in Scomberomorus 



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