GRUBER and COMPAGNO: TAXONOMIC STATUS AND BI01,0(!Y OK BIGEYE THRESHER 



years (i.e., Bailey and Gosline 1955) but their 

 importance in shark systematics was recognized 

 only with the surveys by Springer (1964) and 

 Springer and Garrick (1964). We have compiled 

 available vertebral counts for A. superciliosus 

 (Table 2), which includes five of our specimens. 

 The counts indicate that bigeye threshers of the 

 eastern Pacific and Indian Ocean have slightly 

 higher caudal and probably higher total vertebral 

 counts than bigeye threshers from the western 

 North Atlantic. Considerable variation is found in 

 caudal counts in A. vulpinus from California 

 (230-254, n = 8; Compagno unpubl. data) so 

 that larger samples of vertebral counts of A. 

 superciliosus from different regions will be needed 

 to confirm possible population differences. 



Vertebrae from the monospondylous precaudal 

 region (centra 30-35) were radiographed in 



a bigeye thresher (LJVC-0355), in longitudinal 

 view to show the calcification pattern. As with 

 most other lamnoid sharks the dorsal, ventral, 

 and lateral spaces of the intermedialia, between 

 the diagonal uncalcified areas of the basalia, are 

 composed of longitudinal calcified plates or radii 

 that are distally bifurcated and interleaved with 

 cartilage (terminology follows Ridewood 1921). In 

 A. superciliosus these radii are fewer and 

 less branched than in either A. vulpinus or 

 A.pelagicus, and are not basally fused into a solid 

 mass as in A. pelagicus (Figure 6). 



DENTITION 



Another quantitative character often used in 

 shark systematics is the number of tooth rows in 

 each jaw. We give dental formulas for 22 bigeye 



Table 2. — Vertebral counts of Alopias superciliosus. 



'Abbreviations: NUMBER GH. Hubbell collection; LJVC. L. J. V Compagno collection: MCZ. Museum of Comparative Zoology. Harvard: SHG. 

 Gruber Collection. UMML, University of Miami Marine Laboratory. USNM, United States National Museum of Natural History. Smithsonian 

 Institution. LOCALITY ECP eastern-Central Pacific: ENP eastern Nortti Pacific: SWI, southiwestern Indian Ocean: WNA, western North 

 Atlantic. COUNTS: DC. displospondylous caudal centra. DP. diplospondylous precaudal centra; MP. monospondylous precaudal centra: PC. 

 precaudal (MP + DP) centra; TC. total (MP + DP + DC or PC + DC) centra, 



^Tail of SHG-A7 noticeably shorter: 49°o of the total length 



B 



^>- 



Figure 6. — Radiographs in transverse view of the monospondylous vertebral centra of all three Alopias species: A, A . superciliosus: B, 

 A. vulpinus; C, A.pelagicus. Note the more simple pattern in A. superciliosus. Photo: L. Compagno. 



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