NO. 3539 HAMMERHEAD SHARKS GILBERT H 



patterns resulting from tliese analyses may be valuable indicators of 

 higher relationships in the various groups of vertebrate animals. In 

 the paper by Starr and Fosberg, analyses Avere made of the serum 

 proteins from one specimen of Sphyrna levnni, two specimens of 

 Sphyrna tihuro, two of Rhizoprionodon terraenovae, and two of Aprion- 

 odon isodon. The patterns of the latter two species, both of which 

 are members of the family Carcharhinidae, differed notably from each 

 other and from the patterns in the two species of Sphyrna. On the 

 other hand, the patterns in Sphyrna levnni and S. tihuro showed a 

 marked similarity, thus suggesting a close phylogenetic relationship. 

 It woidd be desirable to rim similar tests on Sphyrna blochii, which is 

 the most divergent species of hammerhead and the one most likely 

 to have evolved independently. Applegate (in litt.), however, informs 

 me that the teeth in S. blochii are similar to those of other hammer- 

 heads, although he has not yet studied the vertebrae of this species. 

 In aU likelihood, the family Sphyrnidae has had a monophyletic origin. 



Sphyrna tudes, Sphyrna corona, and Sphyrna media show a closer 

 phylogenetic relationship than any other species of hammerheads 

 (fig. 4). AU possess a number of common morphological features, 

 some of which are not found in other members of the genus (table 1, 

 figs. 14-22, and pis. 7 c, d and 8). In addition, the three species 

 share several other characters which, although not confined to them 

 alone, fiu-ther demonstrate a close relationship. The form in which 

 the various characters most closely approach those found in the 

 abcrve species is S. tihuro (table 1, figs, 4, 11,21, and 22, and pis. 7 a, b) ; 

 as a result, these four apparently closely related species are grouped 

 together in the subgenus Platysqualus. The respective lengths of 

 the anal fin and anal fin base, the relative lengths of the gill slits, 

 the diameter of the orbit in relation to the distance from the anterior 

 edge of the orbit to the outer margin of the narial opening, the relative 

 positions of the orbits and anterior part of the mouth, the presence 

 of a lower precaudal pit, the appearance of the upper precaudal pit, 

 and several chondrocranial characters all are similar in these fom* 

 species. Finally, the species are comparable in size, all apparently 

 reaching a maximum size of about 5 feet. 



Within the subgenus Platysqnalus, Sphyrna media seems to show 

 a slightly closer relationship to S. tihuro than does S. corona. This 

 assumption is based, first, on the greater overall similarity of the 

 chondrocrania (pis, 7 a-d), as well as similarities in appearance of the 

 anterior-median pore patch (figs. 22e-h). 



The fifth species, Sphyrna blochii, is strikingly different from all 

 other species of Sphyrna in several characters. The extreme expansion 

 of the head, the presence of an outer narial groove, the greatly decreased 

 total number of vertebrae, and the marked enlargement of the verte- 



