Proceedings United States National Museu m

A number of structures have been studied which have proved useful in determining the species of Sphyrna. Finally, different species differ in the presence or absence of a lower paracaudal fossa and the shape of the upper paracaudal fossa.

NO. 3539 HAMMERHEAD SHARKS GILBERT H

In contrast to the relative ease with which the relationships of the foregoing species are distinguished, those of Sphyrna zygaena, S. Despite the difficulties encountered in interpreting the relationships of the above species, appear to be more closely related to each other than to any another group of species of Sphyrna and are therefore included in the subgenus Sphyrna.

NO. 3539 HAMMERHEAD SHARKS — GILBERT 13 the differences in head width have had comparatively httle to do with

Sphyrna tucles, Sphyrna corona, and Sphyrna media, with numerous identical morphological characters, some of which are

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As mentioned earlier, the fins and fin lobes straighten as the shark approaches maturity. The number of young appears to be directly proportional to both the size of the individual and the maximum size of the species.

NO. 3539 HAMMERHEAD SHARKS — GILBERT 21

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3539 HAMMERHEAD SHARK - GILBERT 25 and north to southern China and the southern Philippines (Herre, and from the north to southern China and the southern Philippines (Herre, 1930, p. 142) Cestracion zygaena (misidentification) Radcliffe, p. with description of teeth in illustration as serrations; specimens 12 ft., 6 in. long; Beaufort, N.C.).

HAMMERHEAD SHARKS — GILBERT 27 For many years the species herein called Sphyrna mokarran was

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Sphyrna mokarranis present in the eastern Pacific from the Gulf of California south to Panama and possibly northwestern South America. It occurs in the Pacific from southern Japan south to Australia, although it appears to be absent from New Zealand and the easternmost parts of Oceania.

NO. 3539 HAMMERHEAD SHARKS GILBERT 33

NO. 3539 HAMMERHEAD SHARKS GILBERT 35

Anterior margin of rostral node of chondrocranium nearly straight, or with a broad, very shallow median indentation; accessory cartilage absent; anterior fontanel (viewed ventrally) rather deep and evenly rounded, with no discernible median notch; short, rounded wings present on sides of rostral node; front wing of olfactory cartilage absent, represented only by a small "bump"; anterior part of preorbital process long and slender, and without a sharp angle on the front; posterior part of the preorbital process ends in an evenly rounded knob.

HAMMERHEAD SHARKS GILBERT 37 knows of no authentic record for this species from the Gulf of Mexico

NO. 3639 HAMMERHEAD SHARKS GILBERT 39

The previous confusion resulted from only Griffith's name appearing on the first title page (titled "The Animal Kingdom") as the author of the additions, although the words "andothers" were written in small type below. It is clear from the above that Cuvier had no part in the preparation of these additions, thereby eliminating him as a code descriptor of the species mentioned therein; and therefore Griffith and Smith must be regarded as describers of Sphyrnalewini and other new forms appearing in this volume. Garman seems to have been the first to recognize the distinction between the two species, as in his monograph of the sharks (1913, pp) he described a new hammerhead, Cestracion oceanica, which he noted was "closely related to C .

The length of the inner nasal groove in oceanica, together with other features mentioned in the original description, would suggest that this species is identical to Sphyrna lewini, a suspicion confirmed by examination of the four syntypes (MCZ 460 [3 spec .]; USNM 153587 [1 spec.] ). Although Garman distinguished the young from the above species, there is no evidence that he recognized the adults, a situation that is difficult to understand given that the difference in length of the inner nasal groove that he recognized in the image was in all sizes remains constant.

NO. 3539 HAMMERHEAD SHARKS GILBERT 43 straight or slightly falcate; apex and inner corner of pectoral fin

With the possible exception of the teeth, Sphyrna lewini shows little discernible geographic variation in external morphological features. Those characters considered to be of basic taxonomic importance, such as the structure of the chondrocranium (Fig. 6b), the shape of the anterior-central pore patch on the underside of the head (Fig. 22d), the length and development of the intranarial groove, the position and length of the gill slots and fin shape and position remain fairly unchanged. The toothed condition was long thought to be characteristic only of the Pacific population (Sadowsky, 1965, p. 2) and was in fact one of the reasons Springer named the Atlantic poppidia as a new species, S.

It occurs in the Mediterranean (BigelowandSchroeder, 1948, p. 419) and along the African coast south at least to Liberia and Ghana (Bigelow and Schroeder, 1948, p. 419).

HAMMERHEAD SHARKS — GILBERT 45

The mucal pore lobes on the ventral surface of the head are basically similar in S. The chondrocrania of the two forms are also similar (pis.9a, b), the main difference being in the appearance of the preorbital process. The anterior-median pore lobe on the underside of the head is also unique, the lobe characterized by a sharper but smoothly rounded angle at the posterior corner and by a long, narrow median posterior extension.

Sphyrna tiburois is also distinguished in that the anterior margin of the head is more or less evenly rounded between the legs, with neither median-shaped depression being present; no inner groove; The fourth gill slit is located in front of, and the fifth gill slit is located slightly behind, the insertion of the pectoral fin; posterior lobe of the first dorsal fin ending just before the insertion of the pelvic fin (the dorsal and pelvic fins are closer together only in S. tudes, S. corona and S. media); first dorsal fin relatively slender, not perfectly erect, a line drawn perpendicularly from the tip of the fin barely intersecting the lobe of the fin; base of first dorsal fin about two-thirds of the length of the head and at least half the length of the pectoral fin base; anterior margin of the first dorsally finely evenly curved, the part nearest the apex being more strongly curved; distal edge of first dorsal fin moderately falcate; lobe of the first dorsal fin from four-ninths to almost half the length of the first dorsal fin; origin of the second dorsal fin is located approximately one-third of the way back above the base of the anal fin; the second dorsal fin is quite high, its greatest height being about two-thirds of the length of the base and approximately equal to the greatest height of the anal fin; second dorsal fin base about five-eighths of the anal fin base; lobe of the second dorsal fin rather long, its length about one-third, again the greatest height of the same fin, and extending about two-thirds of the distance from the posterior part of the second dorsal base to the upper precaudal pit; anterior margin of the pectoral fin from half to almost two-thirds of the head length (higher values usually apply to larger individuals); pectoral fin four-fifths as wide as long; pectoral fin base five-eighths to three-quarters length of the anal fin base; anterior margin of pectoralis moderately convex; distal margin of pectoral fins almost straight; tip and inner corner of pectoral muscle rounded; pelvic fin about three-quarters of the analfin; pelvic fin base about three-quarters of the anal fin base; anterior margin of pelvic fin weakly convex; distal edge of pelvic fin very shallow falcate; anal fin.

NO. 3539 HAMMERHEAD SHARKS — GILBERT 49 from the angle included by the upper and lower caudal lobes to

3539 HAMMER-HEAD SHARK - GILBERT 49 from the angle included by the upper and lower caudal lobes to. These counts, which range from 163 to 172 for the latter form and from 142 to 170 for the former, are interesting both because of the wide range of variation found in the typical subgroups and because of the close vertebral agreement. This suggests that those specimens of S. tiburo tiburo from the eastern Gulf of Mexico represent a sibling form that can be distinguished from other populations of the same subspecies only by the number of vertebrae.

Sphyrnatiburo tiburois common in shallow waters, on the western Atlantic coast, where it ranges from southern Brazil to the north. All but three records are from continental waters, and these exceptions are from Bimini, in the western Bahamas, and from Cuba, less than 100 miles from the mainland.

HAMMERHEAD SHARKS — GILBERT 53

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HAMMERHEAD SHARKS GILBERT 55

Panama Bay, offshore between Punta de Hicacal and Rio Pasiga; USNM 50376 (1), no further data

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If we divide the transverse distance between the corners of the mouth by the width of the head, the obtained values are slightly larger for S. The head is moderately expanded, the maximum width measuring from 22.3 to 27.3 percent of TL; character of anterior-median margin of head somewhat variable, evenly rounded in some individuals, without median depression and with wide, very shallow median depression in others; the outer posterior angle of the lateral expansion of the head, located in front of the angle of the mouth; nasal flap broad, bluntly pointed tip, with a broadly curved outer margin that curves strongly inwards; a. Origin of first dorsal fin slightly behind axis of pectoral fin, perpendicular line drawn upwards from origin, intersecting anterior third of pectoral fin; base of first dorsal fin one-third to one-half length of head and about twice length of base of pectoral fin; anterior margin of first dorsal fin broadly and uniformly curved, especially in larger individuals; distal margin of first dorsal fin rather deeply keeled, especially on lower two-thirds of fin; lobe of first dorsal fin two-fifths to one-half length of first dorsal base; the origin of the second dorsal fin is located about two-fifths posteriorly above the base of the anal fin; the second dorsal fin is high, its maximum height about three-quarters the length of the base and three-quarters to four-fifths the maximum height of the fan-fin; second dorsal fin base one-half to five-eighths of anal fin base; lobe of the second dorsal fin rather long, its length about one-third of the maximum height of the fin and extending from two-thirds to three-quarters of the distance from the posterior part of the second dorsal base to the upper part of the precaudal fossa; pectoral fin from two fifths to two thirds of head length (higher values usually apply to larger specimens).

HAMMERHEAD SHARKS — GILBERT 59 perpendicular to the body axis* anterior margin of lower caudal lobe

60 PROCEEDINGS OF THE NATIONAL MUSEUM vol. the first two counts given by Springer, [1940a, p. 163]); upper teeth oblique, becoming more towards the corners of the mouth in the upper jaw; teeth 6 to 9 or 10 longest, outer teeth very low but with a definite point; in the lower jaw, the longest teeth are from 2 to 8 (tooth 1 is not significantly smaller), and the outermost two or three teeth are very short, round and without a definite tip; one or two sets of teeth act in alternating rows on the sides of the upper jaw and two to three rows on the sides of the lower jaw.

NO- 3539 HAMMERHEAD SHARKS — GILBERT 61 allometric change with an increase in length (head width, distance

HAMMERHEAD SHARKS GILBERT 63 53-275 (9), Panama Bay, between Panama City and Punta Gorda;

Sphyrnacorona has one of the most restricted ranges of any hammerhead shark species, occurring only in the eastern Pacific Ocean, from southern Mexico to at least the coast of Colombia (Map 5).

NO. 3539 HAMMERHEAD SHARKS — GILBERT 65

Characters mentioned in the diagnoses of the subgenus Platysqualus and of S. Head moderately expanded, the greatest width measuring from 27.5 to 31.5 percent of TL; inner narialg also extends 3.5 to 4.0 percent of distance from narial openings to median notch; outer posterior corner of lateral extension of head located posterior to. Origin of first dorsal fin slightly posterior to axilla of pectoral fin, perpendicular drawn ventral from origin intersecting anteriorly.

HAMMERHEAD SHARKS — GILBERT 67 third of pectoral fin; base of first dorsal fin three-eighths to four-ninths

NO.3539 HAMMER-HEAD SHARK — GILBERT 69caudal appearing relatively narrow and long, distance from tail appearing relatively narrow and long, distance from included angle of upper and lower tail to last tip, going about IK times in anteriormarginulja long above singleloudalolobar; al lobe rather elevated, sloping posteriorly at an angle of 25 to 30° from a perpendicular to the body axis; anterior margin of lower caudalobe slightly convex; posterior marginolule lobe straight. for lectotype); upper teeth oblique, becoming more and more towards the corners of the mouth in the upper jaw; teeth 4 or 5 to 11 longest, outer teeth very low but with defined edges; lower teeth 2 to 7 or 8 longest, outermost shortest, rounded, without distinct cusp; one or two series of functional teeth in alternating rows along the jaw on the sides of the flower and two to three rows on the sides of the lower jaw. Cutaneous teeth (examined from upper back below first dorsalfin) equal and narrow, overlapping but little, blades rather thick and strongly arched; small specimens with three, larger specimens usually up to five, sharp-pointed ridges, and very sharp-pointed marginal teeth (especially deeply pointed and pointed in small individuals) on denticles; Median tooth on denticle slightly longer than distal one; legs and feet and thinner.

Examination of the lectotype (listed elsewhere in this paper) of Zygaenatudes, a 346 mm. female from Nice, France, shows that Mediterranean and West Atlantic populations of Sphyrna tudes are morphologically indistinguishable.

NO. 3539 HAMMERHEAD SHARKS — GILBERT 73

NO. 3539 HAMMERHEAD SHARKS — GILBERT 75

Occurrence of the hammerhead shark at Provincetown and at Chatham, Mass.] Proc.BostonSoc.Nat.Hist., vol.3, pp.70-71.

HAMMERHEAD SHARKS — GILBERT 79 Table 2

HAMMERHEAD SHARKS — GILBERT 81

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Radiographs of chondrocrania of Sphyrnatudes: A, a specimen 390 mm.TL (holotype of S. bigelowi) from Uruguay (USNM87682); B, one specimen 346 mm.TL (lectotype of S.tudes) from France (MNHN 1049).