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paleopedia:

The goblin Shark, Mitsukurina owstoni (1898)

Phylum : Chordata
Class : Chondrichthyes
Subclass : Elasmobranchii
Order : Lamniformes
Family : Mitsukurinidae
Genus : M. owstoni

• Middle Eocene/Recent (37 - 0 Ma) Least concern
• 3 m long and 210 kg (size)
• Oceans worldwide (map)

Phylogenetic studies based on morphology have generally placed the goblin shark as the most basal member of the order Lamniformes, known as mackerel sharks. Studies using genetic data have also supported a basal position for this species. The family Mitsukurinidae, represented by Mitsukurina, Scapanorhynchus, and Anomotodon, dates back to the Aptian age of the Cretaceous period. Mitsukurina itself first appears in the fossil record during the Middle Eocene extinct species include M. lineata and M. maslinensis.Striatolamia macrota, which lived in warm shallow waters during the Paleogene, may also be a Mitsukurina species. As the last member of an ancient lineage, and one that retains several “primitive” traits, the goblin shark has been described as a “living fossil”.

The goblin shark has a distinctively long and flattened snout, resembling a sword blade. The proportional length of the snout decreases with age. The eyes are small and do not have protective nictitating membranes; behind the eyes are spiracles. The large mouth is parabolic in shape. The jaws are highly protrusible and can be extended almost to the end of the snout, though normally they are held flush against the underside of the head. There are 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. There is much among-individual variation in tooth length and width, in whether the teeth have a smaller cusplet on each side of the main cusp, and in 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.

The body is fairly slender and flabby. The two dorsal fins are similar in size and shape, both being small and rounded. The pectoral fins are also rather small and rounded. The pelvic and anal fins have long bases and are larger than the dorsal fins. The caudal peduncle is flattened from side-to-side and lacks keels or notches. The asymmetric caudal fin has a long upper lobe with a shallow ventral notch near the tip, and an indistinct lower lobe. The soft, semi-translucent skin has a rough texture from a covering of dermal denticles, each shaped like a short upright spine with lengthwise ridges. In life, this species is pink or tan due to visible blood vessels beneath the skin; the color deepens with age, and young sharks may be almost white. The fins’ margins are translucent gray or blue, and the eyes are black with bluish streaks in the iris. After death, the coloration quickly fades to dull gray or brown.