The goblin shark is a rare species of deep-sea shark. Sometimes called a “living fossil”, it is the only extant representative of the family Mitsukurinidae, a lineage some 125 million years old.
This pink-skinned animal has a distinctive profile with an elongated, flat snout, and highly protrusible jaws containing prominent nail-like teeth. It is usually between 3 and 4 m (10 and 13 ft) long when mature, though it can grow considerably larger such as one captured in 2000 that is thought to have measured 6 m (20 ft). Goblin sharks are benthopelagic creatures that inhabit upper continental slopes, submarine canyons, and seamounts throughout the world at depths greater than 100 m (330 ft), with adults found deeper than juveniles.
Some researchers believe that these sharks could also dive to depths of up to 1,300 m (4,270 ft), for short periods of time.
They are old as dinosaurs
Around 125 million years ago, in the late Mesozoic epoch, the Mitsukurinidae family first emerged. This was around the time dinosaurs were on earth. The oldest Mitsukurina fossils date back 49–37 million years to the middle Eocene. The fossil species Mitsukurina lineata and Mitsukurina maslinensis have been identified so far.
The goblin shark has a distinctively long and flat snout, resembling a blade. The proportional length of the snout decreases with age. The eyes are small and lack protective nictitating membranes; behind the eyes are spiracles. The large mouth is parabolic in shape.
The jaws are very protrusible and can be extended almost to the end of the snout, though normally they are held flush against the underside of the head. It has 35–53 upper and 31–62 lower tooth rows. The teeth in the main part of the jaws are long and narrow, particularly those near the symphysis (jaw midpoint), and are finely grooved lengthwise. The rear teeth near the corners of the jaw are small and have a flattened shape for crushing.
Much individual variation of tooth length and width occurs, as for whether the teeth have a smaller cusplet on each side of the main cusp, and regarding the presence of toothless gaps at the symphysis or between the main and rear teeth. The five pairs of gill slits are short, with the gill filaments inside partly exposed; the fifth pair is above the origin of the pectoral fins
What do Goblin Sharks eat?
The goblin shark feeds mainly on teleost fishes such as rattails and dragonfishes. It also consumes cephalopods and crustaceans, including decapods and isopods. Garbage has been recorded from the stomachs of some specimens. Its known prey includes bottom-dwelling species such as the blackbelly rosefish (Helicolenus dactylopterus), and midwater species such as the squid Teuthowenia pellucida and the ostracod Macrocypridina castanea rotunda. Thus, the goblin shark appears to forage for food both near the sea floor and far above it.
Since it is not a fast swimmer, the goblin shark may be an ambush predator. Its low-density flesh and large oily liver make it neutrally buoyant, allowing it to drift towards its prey with minimal motions so as to avoid detection. Once prey comes into range, the shark’s specialized jaws can snap forward to capture it.
The protrusion of the jaw is assisted by two pairs of elastic ligaments associated with the mandibular joint, which are pulled taut when the jaws are in their normal retracted position; when the shark bites, the ligaments release their tension and essentially “catapult” the jaws forward. At the same time, the well-developed basihyal on the floor of the mouth drops, expanding the oral cavity and sucking in water and prey. Striking and prey capture events were videotaped and recorded for the first time during 2008 and 2011 and helped to confirm the use and systematics of the protrusible jaws of goblin sharks.
The video evidence suggests that while the jaws are definitely unique, goblin sharks use ram feeding, a type of prey capture that is typical of many mackerel sharks. What makes the goblin shark unique is the kinematics of their jaw when feeding. The lower jaw seems to undergo more complex movements and is important in capturing the prey. The measured protrusions of the upper and lower jaw combined put the goblin shark jaws at 2.1–9.5 times more protrusible than other sharks.
The lower jaw has a velocity about two times greater than the upper jaw because it not only protrudes forward, but also swings upward to capture the prey, and the maximum velocity of the jaws is 3.14 m/s. The goblin shark has a re-opening and re-closing pattern during the strike, a behavior that has never been seen in other sharks before and could be related to the extent with which the goblin shark protrudes its jaws. This “slingshot” style of feeding could be an adaptation to compensate for poor swimming ability by allowing the goblin shark to catch elusive, fast prey without having to chase the prey.
Little is known about goblin shark reproduction because a pregnant female has yet to be found and studied. It likely shares the reproductive characteristics of other mackerel sharks, which are viviparous with small litter sizes and embryos that grow during gestation by eating undeveloped eggs (oophagy).
The birth size is probably close to 82 cm, the length of the smallest known specimen. Males mature sexually at about 2.6 m (8.5 ft) long, while female maturation size is unknown. No data is available concerning growth and aging. Some researchers have estimated, based on their own research and prior findings, that male goblin sharks mature at approximately 16 years old and can live up to 60 years.