lamniformes - rdsinc.com... in contrast to the single extant carcharodon car-charias. however, the...

Evolution and systematicsLiving lamniform sharks are mere remnants of a much

greater lamniform lineage that has, for the most part, becomeextinct. The 15 surviving species pale in comparison to thecountless hundreds that have been described from fossil re-mains; the genus Carcharodon alone is known from some 10fossil species, in contrast to the single extant Carcharodon car-charias. However, the overwhelming majority of these fossilsconsist of isolated teeth, first appearing in the fossil recordduring the early Cretaceous period some 120 million yearsago (mya). Fossil lamniform teeth are known from many wide-spread marine localities from all continents, and they resem-ble those of living mackerel sharks in usually being slender,with very sharp cusps and arched roots. Many living lamni-form species have closely related fossil relatives, again knownonly from teeth, going back at least to the Paleocene epoch(some 62 mya). Some of these fossil species are even placedin genera that are still extant (e.g., Carcharodon, Odontaspis),corroborating that lamniform sharks have a remarkably longevolutionary history, as do most living shark groups.

Fossil lamniforms known from more complete remains areextremely rare and include preserved partial skeletons of gob-lin sharks (Mitsukurinidae) from Lebanon (about 90 millionyears old), and vertebrae of various taxa, such as the megalodonshark from Europe (of Miocene to Pliocene age, some16 to 2.6mya). The late Cretaceous goblin shark (Scapanorhynchus lewisi)is similar to the living goblin species (Mitsukurina owstoni) inhaving a very elongated snout, but it differs in having a muchlonger anal fin and more angular dorsal fins. Moreover, somefeatures of its teeth and denticles differ as well. The megalodonshark (Carcharodon megalodon) is the most notorious fossil lam-niform. It is known from huge, triangular teeth (as large as 7.9in [20 cm] in height), that are very similar to teeth of the liv-ing white shark (Carcharodon carcharias). The megalodon shark,however, was much larger (estimated to reach up to 49 ft [15m] in length), some three times the size of the living white, and

was one of the greatest marine predators of all time (and thegreatest macropredatory shark). Reconstructions of its jaws, be-lieved to have been able to fit several people when agape, fea-ture in many museum exhibits. Megalodon fossils are knownfrom North and South America, the Caribbean, Europe, Aus-tralasia, Japan, and Africa.

Among living elasmobranchs (sharks and rays), lamniformsharks are more closely related to the ground sharks (Car-charhiniformes), bullhead sharks (Heterodontiformes), andcarpet sharks (Orectolobiformes). These four orders, unitedin the larger group Galeomorphii, share various evolutionaryinnovations, such as the unique placement of the hyoman-dibula (a cartilage supporting the jaws posteriorly) on theskull. Within this group, lamniforms are most closely relatedto the ground sharks, as both orders share a tripodal rostrumsupporting the snout internally.

Living lamniforms are among the most intensely studiedand best-known sharks. Four of the living species were de-scribed in the eighteenth century, five in the nineteenth, andsix in the twentieth century. (The last species described wasthe megamouth shark in 1983.) They are currently dividedinto seven families, 10 genera, and 15 species, and they werefirst recognized as a unique group by American ichthyologistDavid Starr Jordan (1851–1931) in 1923.

Phylogenetic (evolutionary) relationships among lamni-form genera also have received much recent attention. Thegoblin shark (Mitsukurina) is considered the most basal, orprimitive, living lamniform, followed by the sand tiger sharks(family Odontaspididae) and the crocodile shark (Pseudo-carcharias). The remaining mackerel sharks have plesodic pectoral fin skeletons, in which the internal supports extendto the distal fin margin. Recent phylogenetic theories alsosupport a common ancestry for a lamniform subgroup—comprising the basking shark and lamnids—with lunate cau-dal fins. Phylogenetic studies based exclusively on charactersfrom the teeth disagree to some extent with those based on

Grzimek’s Animal Life Encyclopedia 131

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Lamniformes(Mackerel sharks)

Class Chondrichthyes

Order Lamniformes

Number of families 7

Photo: A basking shark (Cetorhinus maximus)feeding on plankton in the Irish Sea. (Photo byJeff Rotman/Photo Researchers, Inc. Reproducedby permission.)

the skeleton, but teeth can often be misleading as indicatorsof evolutionary relationships in sharks and rays. Molecularphylogenies are also partly at odds with morphological ones,indicating that the evolutionary history of many lamniformgenera is still in dispute.

Physical characteristicsMackerel sharks are moderate to very large, ranging from

about 3.3 ft (1 m) to 49 ft (15 m) in length. Some mackerelsharks, such as the great white and shortfin mako, are amongthe most popularly known and easily recognizable of allsharks. Other mackerel sharks are among the most bizarreand anatomically unique sharks, such as the megamouth, gob-lin, and thresher sharks. Lamniform sharks have unique teethand intestines with a ring valve (with numerous, closelystacked turns).

There is some variation among lamniform species in rela-tion to body and fin profiles, but all mackerel sharks have twodorsal fins (usually the first dorsal fin is very tall, while the

second is reduced in height), large pectoral fins (except in thegoblin and crocodile sharks, and to a lesser degree in the sandtiger sharks), and a small anal fin (except in the goblin andsand tiger sharks). The caudal fin is lunate or semilunate (i.e.,with a well developed lower lobe) and upright in some species(basking shark and lamnids). Thresher sharks have caudal finsabout equal to the length of the body, and goblin, sand tiger,megamouth, and crocodile sharks have caudal fins with rela-tively small lower lobes. The snout is conical in most species(except in the megamouth shark), and paddle shaped in thegoblin shark; internally the snout is supported by a tripodalrostrum, usually composed of three cartilaginous segments.The spiracles are extremely reduced. The eyes are black andround in most species and lack nictitating (protective) mem-branes. Five pairs of gill openings are present. Denticles alongthe body are very small and do not form larger spines.

Some lamniform species, particularly those of the familyLamnidae (white, porbeagle, salmon, and mako sharks) are ca-pable of maintaining slightly elevated body temperatures in re-lation to the surrounding water. This is accomplished in amanner similar to tunas and mackerels (bony fishes of the family Scombridae), through a counter-current, vascular heat-exchange system. The body musculature, viscera, brains, andeyes remain at temperatures from 5.4°F (3°C) to 25.2°F (14°C)warmer than ambient water. This physiological mechanism en-ables lamnid mackerel sharks to maintain higher metabolicrates; hence they are capable of great bursts of activity.

Lamniforms are usually blue or blue-gray on their dorsaland lateral sides, but white to off-white ventrally. Well-defined spots and blotches are mostly absent, but the whiteshark has black ventral pectoral fin extremities, and some speciesmay have whitish blotches on the tail; the salmon shark, Lamnaditropis, has brown blotches on its lateral and ventral aspects.

DistributionMackerel sharks are found worldwide in tropical and tem-

perate marine waters. Some species penetrate boreal and sub-antarctic seas (basking shark and species of the genus Lamna),and other species are extremely wide-ranging, such as theshortfin mako and white shark. All species are somewhat wide-spread.

HabitatMackerel sharks are present in shallow, coastal waters, as

well as epipelagically and mesopelagically in deeper oceanicwaters. Most species, such as the mako, white, and sand tigersharks, occur predominantly in shallow areas, while others aredemersal inhabitants of continental slope regions (e.g., thegoblin shark).

BehaviorThe behavior of sharks that inhabit oceanic realms is gen-

erally not well known. Lamniform sharks, however, displaydifferent behaviors in relation to feeding (from filter feedingto predation), as well as in relation to metabolism. The more

132 Grzimek’s Animal Life Encyclopedia

Vol. 4: Fishes IOrder: Lamniformes

A white shark (Carcharodon carcharias) approaches its prey from be-low where its gray topside camouflages its approach. (Photo by Cor-bis. Reproduced by permission.)

active species are laeterothermic (slightly warm-blooded); as aresult they can swim at astounding speeds and are capable ofgreat bursts of energy. The filter-feeding species, however, arerelatively sluggish. Many species of lamniforms are known toleap completely out of the water (breaching), and not only asa result of being hooked on a line. The reasons behind thisbehavior are largely unknown but may have to do with escap-ing predators, snatching prey (as in the white shark), or rid-ding themselves of parasites. A lunate caudal fin may facilitatethe strong upward swimming necessary to breach the watersurface. Segregation by sex and size has been recorded in lam-niform sharks, but much is yet to be learned about their pop-ulation dynamics. More specific behavioral patterns have beendescribed for particular species in the species accounts below.

Feeding ecology and dietAlmost all mackerel sharks are predaceous, extremely ac-

tive eaters, feeding mostly on fishes belonging to numerousfamilies (both bony fishes as well as sharks and rays), but alsoconsuming large amounts of invertebrates (e.g., squids, oc-topi, gastropods, crustaceans) as well as marine mammals (pin-nipeds, dolphins, and whales, as well as whale carcasses),marine turtles, and even oceanic birds. In contrast, twospecies, the megamouth and basking sharks, feed almost ex-clusively on zooplankton, and current evolutionary theoriesindicate that filter feeding evolved independently in bothspecies, which also differ in their mode of filter feeding. Lam-niform sharks are preyed upon by other shark species, in-cluding their own species.

Reproductive biologyAs far as is known, all species of mackerel sharks are yolk-

sac viviparous (ovoviviparous, aplacentally viviparous); i.e.,they give birth to live young that develop in utero and thatfeed on the yolk contents of their yolk sacs. But in many lam-niform species, intrauterine cannibalism has been confirmedor is suspected. This occurs when embryos prey on each other(adelphophagy) or on other eggs (oophagy) inside the uterusafter their yolk reserves are depleted. This group is the onlyelasmobranch taxon in which this occurs. Adelphophagy is

known for certain in only one species, Carcharias taurus, butis suspected in others. Gestation periods vary among speciesand are comparatively poorly known. In some species, femalesare gravid from eight months to one year, while other specieshave longer gestations (up to 18 months). A period of repro-ductive inactivity may follow a gestation. Courtship patternsare presumably similar to those in many other sharks, withmales biting females to subdue them prior to copulation andalso during copulation.

Conservation statusThe following species are listed by the IUCN: Alopias

vulpinus, Lamna ditropis, Megachasma pelagios, and Odontaspisnoronhai (as Data Deficient); Carcharodon carcharias, Carchariastaurus, and Cetorhinus maximus (as Vulnerable); Lamna nasus,Isurus oxyrinchus, and Pseudocarcharias kamoharai (as LowerRisk/Near Threatened).

Significance to humansMany lamniform species are captured on longlines or

trawls, either as bycatch or as specific targets, by the com-mercial fishing industry. The flesh is consumed fresh, frozen,smoked, or dried-salted, and their fins are procured by thedestructive shark fin soup industry. Sport fishing for makosand other lamniforms is also common. This order containswhat has been considered to be the most dangerous sharkspecies, the white shark. But the misguided, anthropocentricperception that the white shark and other lamniform speciesare potential “man-eaters” has faded in the past decade; thisnegative image was given to this species mostly by sensation-alistic media. Ironically, the roles are presently reversed, as itis now well understood that it is the sharks that are the vic-tims of humankind, mostly through overfishing and the ruth-less, cruel, shark fin soup fad, and not the other way around.In fact, many species of lamniforms and other sharks are quitevaluable alive. The sand tiger shark is important as an exhi-bition fish in public aquaria, where it is relatively easily keptfor long periods. Many lamniforms, such as the sand tiger,white, thresher, basking, and mako sharks, are even commonecotourist attractions in many places around the world.


Order: LamniformesVol. 4: Fishes I


2

3

4

1

5

6

7

8 9

1. Shortfin mako (Isurus oxyrinchus); 2.White shark (Carcharodon carcharias); 3. Sand tiger shark (Carcharias taurus); 4. Crocodile shark (Pseudo-carcharias kamoharai); 5. Porbeagle (Lamna nasus); 6. Megamouth shark (Megachasma pelagios); 7. Thresher shark (Alopias vulpinus); 8. Gob-lin shark (Mitsukurina owstoni); 9. Basking shark (Cetorhinus maximus). (Illustration by Brian Cressman)

Thresher sharkAlopias vulpinus

FAMILYAlopiidae

TAXONOMYSqualus vulpinus Bonnaterre, 1788, Mediterranean Sea.

OTHER COMMON NAMESFrench: Renard; Spanish: Zorro.

PHYSICAL CHARACTERISTICSA very characteristic, large shark that may reach over 19.7 ft (6m) in length, with an extremely elongated caudal fin (as long asthe body), prominent first dorsal fin, minute second dorsal andanal fins, long pectoral fins, and small, conical snout. Col-oration blue-gray to dark gray dorsally and laterally, with awhite abdominal region, and white blotches laterally anteriorto tail.

DISTRIBUTIONCircumglobal in both coastal and oceanic, tropical to temper-ate, waters.

HABITATUsually occurs over the continental shelf region, close to thesurface, but also occupying oceanic waters down to a depth of

1,200 ft (366 m). Younger specimens are more commonlyfound inshore.

BEHAVIORThresher sharks are swift, vigorous swimmers, capable ofbreaching. They segregate by sex and migrate seasonally offthe western coast of North America.

FEEDING ECOLOGY AND DIETPreys mostly on a wide variety of epipelagic, midwater, and de-mersal fishes, but known to feed also on squid, octopi, pelagiccrustaceans, and even seabirds. Uses its long tail to stun prey,entrapping them by swimming in increasingly smaller circlesaround schools of fishes, sometimes even in tandem with an-other thresher shark.

REPRODUCTIVE BIOLOGYYolk-sac viviparous, embryos apparently are uterine cannibals(oophagy). Litter numbers range from two to six, most com-monly four; three to seven have been recorded in the easternAtlantic. Young remain for a short period in shallow waternursing grounds. A gestation period of nine months has beenreported for California populations, where mating occurs inthe summer. Individuals are sexually mature between three andeight years old. Individuals may live for 50 years.

CONSERVATION STATUSListed as Data Deficient by the IUCN.


Species accounts


Alopias vulpinus

Carcharodon carcharias

Isurus oxyrinchus

SIGNIFICANCE TO HUMANSCaught by both commercial (mostly with longlines) and recre-ational fisheries, and consumed (or have been) in somewhatregular quantities in many locations, from almost all majoroceans. Heavily fished off the West Coast of the United Statesin the late 1970s, but because overfishing led to a significantdecline in stocks, the targeted fishery was terminated in 1990,though they were still captured as bycatch. Not considereddangerous, but they command respect because of their largesize and possible aggressiveness. ◆

Basking sharkCetorhinus maximus

FAMILYCetorhinidae

TAXONOMYSqualus maximus Gunnerus, 1765, Norway.

OTHER COMMON NAMESFrench: Pélerin; Spanish and Portuguese: Peregrino.

PHYSICAL CHARACTERISTICSAn unmistakable, huge shark, with extremely elongated gillslits (reaching from the dorsal to the ventral side), a very widegill region when gills are expanded during feeding, a large, ca-pacious mouth, well-developed gillrakers on the inside of thegills to capture small food particles, very small teeth, elongatedpectoral fins, and a large lunate caudal fin. Grayish in color allaround. Reported to reach 40–50 ft (12.2–15.2 m) in length,but large specimens are more common at about 33 ft (10 m).

DISTRIBUTIONWorldwide in mainly coastal, cold, temperate waters, mostabundant off both sides of the northern Atlantic, but also inwarmer, subtemperate regions such as the MediterraneanSea.

HABITATUsually found over relatively shallow, coastal, pelagic watersbut can be caught in open seas over deeper waters. Baskingsharks appear in regular periods in certain areas (probably tofeed) but also disappear in what appears to be regular cycles.Where they “disappear” to is a mystery, and perhaps they “hi-bernate” or spend periods of relative inactivity on or close tothe bottom of the ocean.

BEHAVIORBasking sharks have been seen to leap clear out of the water (ashave other mackerel sharks). Usually they are observed cruisingat about 2.3 mph (2 knots) near or at the surface, with theirmouths open during feeding. They are highly migratory, andseveral individuals may swim in tandem.

FEEDING ECOLOGY AND DIETA filter-feeding shark, capable of taking in massive amounts ofzooplankton. It swims with its mouth open very wide, retainingfood items on its gillrakers, which are covered by denticles,giving them a rough texture. The gillrakers are shed periodi-cally, usually in the early winter. Basking sharks feed mostly inthe summer months near the surface. They either feed by al-ternative means when the gillrakers are shed, or remain with-out feeding, inactive, until they are regenerated. Food isretained in the gillrakers, aided by secretions of mucus in thepharynx, and subsequently swallowed when the mouth isclosed.


Vol. 4: Fishes IOrder: Lamniformes

Carcharias taurus

Cetorhinus maximus

Megachasma pelagios

REPRODUCTIVE BIOLOGYBasking sharks employ yolk-sac viviparity, giving birth to twoto six pups per gestation. The pups are the largest of all sharkspecies, ranging 59–67 in (150–170 cm) in total length. Gesta-tion periods are mostly unknown but are estimated to be verylong (more than 1 year). The ovaries produce huge quantitiesof eggs.

CONSERVATION STATUSListed as Vulnerable by the IUCN and protected in theUnited Kingdom, Malta, United States (East Coast), and NewZealand. Protection is pending in other areas (MediterraneanSea, South Africa).

SIGNIFICANCE TO HUMANSThe basking shark has been captured in much of its range sincethe nineteenth century for its oily liver, which may contain upto 500 gal (1,893 l), meat (fresh and dried-salted), and skin, andalso for its fins for the abhorrent shark fin–soup industry. Popu-lations of the basking shark have declined significantly in manyregions. The basking shark has some importance for thetourism trade, as it can be seen in many places, especially in thenorthern Atlantic (e.g., Bay of Fundy, Cape Cod, Isle of Man).Harmless, this shark poses no direct danger to people, but de-serves respect because of its large size. ◆

White sharkCarcharodon carcharias

FAMILYLamnidae

TAXONOMYSqualus carcharias Linnaeus, 1758, Europa.

OTHER COMMON NAMESEnglish: Great white shark; French: Grand requin blanc; Span-ish: Jaquetón blanco.

PHYSICAL CHARACTERISTICSVery large, reaching to 21.3 ft (6.5 m), more commonly to 18ft (5.5 m), with a distinctive dentition comprised of large, tri-angular teeth with serrations on both edges, and with lateralcusps in embryos. They have a conspicuous white ventral col-oration and a gray-to-bluish dorsal and lateral shade (the ven-tral and dorsal colorations are clearly separated on the sides),large gill slits, well-developed precaudal keels, a large first dor-sal fin (much larger than the second), large and lunate caudalfin, pectoral fins with black tips ventrally, a conical snout, anda large, black eye.

DISTRIBUTIONWorldwide in coastal marine waters, and also around oceanictropical islands, but more common in cold and warm temper-ate regions, and apparently rare or absent from most of thewestern Indian Ocean, Indonesia, and tropical Central Amer-ica. Most common off California, Australia, and South Africa.Compared to other shark species, the white shark is relativelyuncommon where it occurs.

HABITATThe white shark is primarily a continental shelf inhabitant,cruising through relatively shallow waters either near the sur-face or close to the bottom. It also is found off oceanic islandsand inshore bays and has even been captured on a bottom

longline as far down as 4,199 ft (1,280 m). Capable of wide ex-cursions in the pelagic realm.

BEHAVIORWhites are solitary and nomadic, and may occur in pairs, butfeeding aggregations of some ten individuals also have beenobserved. It is known that they will leap completely out of thewater (breaching) when capturing surface prey (or perhaps forother reasons). They are even capable of breaching vertically ina manner similar to dolphins. “Spy hopping” (when the sharkwill maintain its head out of the water as if to search the sur-roundings) and “repeated aerial gaping” (RAG; when the shark“bites” the air with its head clear out of the water) also havebeen observed. The white shark is known to satisfy its curiosityby circling intended prey items, or even boats and divers. It iscapable of great bursts of speed. While feeding, their eyes rollback in their sockets. There may be segregation of individualsaccording to size.

FEEDING ECOLOGY AND DIETThe white shark is a formidable predator, feeding mainly onnumerous families of bony fishes (as well as a large variety ofsharks, even the basking shark), sea turtles, marine mammals(pinnipeds and whale carcasses), and even sea birds resting onthe surface. Invertebrates also may be eaten (such as crabs), butmost of its food comes from fishes and marine mammals takenfrom the surface or in the water column. White sharks are oneof the top predators in the ocean; however, they sometimes fallprey to orcas (killer whales).

REPRODUCTIVE BIOLOGYEmbryos develop inside the uteri (yolk-sac viviparous), and in-trauterine cannibalism (oophagy) is confirmed, as embryos havebeen found to have great amounts of yolk and egg membranesin their stomachs. Teeth also have been found in the stomachsof embryos, but embryos are believed to swallow their ownteeth during development, as they undergo tooth replacementseveral times before birth. Gestation periods are mostly un-known. A litter of nine pups was reported for one pregnant fe-male from the Mediterranean, and up to 10 embryos mayreach term (data from gravid Japanese whites). The lack ofknowledge concerning their reproduction is due to the scarcityof gravid females, perhaps an indication of pronounced segre-gation during gestation, or even of low fecundity. Size at matu-rity for females is between 13.1 ft (4 m) and 16.4 ft (5 m) long,and between 11.5 ft (3.5 m) and 13.1 ft (4 m) for males. Age atmaturity ranges from 12 to 14 years for females and nine to 10for males. Embryos measure 4 ft (1.2 m) to 5 ft (1.5 m) atbirth, and can weigh up to 55 lb (25 kg). Courtship has beenobserved in one instance; the male bit the female into submis-sion preceding a 40-minute-long copulatory embrace.

CONSERVATION STATUSPresently threatened in many locations (e.g., Australia, SouthAfrica) and heavily protected in Australia, South Africa,Namibia, Israel, Malta, and the United States. Australia is ap-parently the only country in which there is a detailed recoveryplan for this species. Whites are listed as Vulnerable by theIUCN.

SIGNIFICANCE TO HUMANSThe white shark is perhaps the most notorious of all sharks,with an undeserved reputation as a “man-eater” and threat tohumans. There are attacks on humans attributed to this speciesevery year, but they average only about three per year from1952 to 1992 (increasing slightly towards 1999). Attacks by thewhite are rare, however, when the whole phenomenon of



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