Collette and Gillis Osteological differences between two species of Orammatorcynus 



Figure 19 



Quadrate and symplectic in Grammatorcynus. (a) G. biliine- 

 atus, Western Australia, 460 mm FL; (b) G. bicarinatus, 

 Queensland, 563 mm FL. 



hypohyals, ceratohyal, and epihyal are closely associ- 

 ated and form a functional unit. 



Hypohyals The hypohyals comprise separate 

 dorsal and ventral elements joined longitudinally. In 

 lateral view, the ventral hypohyal is clearly larger than 

 the dorsal hypohyal in Grammatorcynus, but in Scom- 

 beromorus not quite as large relative to Grammatorcy- 

 nus. In Acanthocybium the ventral hypohyal is three 

 times larger than the dorsal hypohyal. Laterally, the 

 suture that runs between the dorsal and ventral hypo- 

 hyals curves ventrally at various angles in Gramma- 

 torcynus and Scomberomorus, but runs almost hori- 

 zontally in Acanthocybium. Mesially, a pointed lateral 

 process at the anterodorsal end of the dorsal hypohyal 

 forms a symphysis with the glossohyal, urohyal, basi- 

 branchial, and the process of the hypohyal from the 

 opposite side in Grammatorcynus and Scomberomorus. 

 Acanthocybium also has a pointed lateral process, but 

 it appears to be further posterior due to also having 

 an anterior pointed end to the hypohyals at the junc- 

 tion of the dorsal and ventral hypohyals. In addition, 

 Acanthocybium has a prominent anterolateral process 

 on the ventral hypohyal. The groove for the hyoidean 

 artery runs along the outer surface of the epihyal, 

 ceratohyal, and ventral portion of the dorsal hypo- 

 hyal. In Grammatorcynus the groove in the dorsal 

 hypohyal is relatively short, extending anteriorly 

 11-39% of the length of the dorsal hypohyal before 

 becoming a covered tunnel leading to the inner side of 

 the dorsal hypohyal. In Scomberomorus the groove 

 extends 32-53% before becoming a tunnel to the inner 

 side, and in Acanthocybium the groove extends 29-47% 

 before becoming a foramen leading to the inner side. 

 The opening on the inner side appears as a small to 

 moderate pit, usually located in the ventral portion of 



the dorsal hypohyal in Grammatorcynus and Scom- 

 beromorus. 



Ceratohyal The ceratohyal is a long flat bone, 

 broadest at the posterior end, and with an anteroven- 

 tral projection that articulates with the posteroventral 

 notch of the ventral hypohyal. It is the largest bone 

 of the hyoid complex. Posteriorly, the middle part of 

 the ceratohyal interlocks with the epihyal by means of 

 odontoid processes issuing from both elements 

 (ceratohyal-epihyal suture of McAllister 1968), while 

 the upper and lower portions are joined by cartilage. 

 Four acinaciform branchiostegal rays are attached to 

 the respective articular surfaces along the concave 

 middle portion of the ventral margin in Gramma- 

 torcynus and Acanthocybium.. In Scomberomorus the 

 fifth branchiostegal ray is also usually attached to the 

 ceratohyal (most posterior part) or on the space be- 

 tween the ceratohyal and epihyal, not on the anterior 

 part of the epihyal. In Grammatorcynus and Acantho- 

 cybium the fifth branchiostegal ray is on the anterior 

 part of the epihyal. The hyoidean groove runs the 

 length of the ceratohyal on its lateral surface. The 

 groove is so deep in 10 species of Scomberomorus 

 (brasiliensis, commerson, concolor, multiradiatus, 

 munroi, niphonius, queenslandicus, semifasciatus, 

 sierra, and tritor) that it forms a thin slit through the 

 bone, the ceratohyal window or "beryciform" foramen. 

 This slit is rare in Grammatorcynus and Acantho- 

 cybium, and is either rare or occasional in the other 

 eight species oi Scomberomorus . The dorsal margin of 

 the ceratohyal is usually concave, but sometimes flat 

 in Grammatorcynus. It is deeply concave in Acan- 

 thocybium, and varies from concave to convex in 

 Scomberomorus. 



Epihyal The epihyal is a triangular bone that 

 interlocks anteriorly with the ceratohyal and has a 

 posterior process that articulates with the interhyal. 

 Three branchiostegal rays articulate wdth the epihyal 

 in Gramm.atorcyyius and Acanthocybium. Only two 

 branchiostegal rays are found on the ventral portion 

 of the epihyal in Scomberomorus. In Grammatorcynus 

 the depth of the epihyal is 66-80% of the length from 

 the smooth anterior margin of the bone to the tip of 

 the posterior process. Epihyal depth is narrowest in 

 Acanthocybium (58-62%), and in Scomberomorus it 

 varies from 68% in S. commersoyi and S. cavalla to 98% 

 in S. koreanus, vnth intermediate values for the other 

 species. 



Interhyal The interhyal is a small flattened 

 bone that is attached to the epihyal dorsal to the 

 posterior process. It is directed obliquely upward and 

 links the hyoid complex to the hyomandibula and 

 symplectic. No differences in interhyals were noted. 



Glossohyal The glossohyal (basihyal) is a 

 median bone that supports the tongue and overlies the 



