Sharks The Animal Answer Guide

224 Sharks: The Animal Answer Guide

tions of dead sharks). So among the poorly known species are some lam-

noid sharks (White, Megamouth); most carcharhiniforms; the hundreds

of deep-sea sharks, including Frilled Sharks (Chlamydoselachus anguineus),

goblin sharks, and sleeper sharks; and most skates and rays (including the

highly endangered sawfishes and chimaeras). Rare, usually small elasmo-

branchs, too numerous to mention, would add greatly to the list.

How do scientists tell sharks apart?

Taxonomy is the science devoted to identifying, describing, and naming

organisms. Taxonomists develop the identification guides that other people

use to tell sharks apart.

If you look in such a guide to the species of sharks, you will often find at

the outset a “comparative key to species” of a particular region, nation, or

even the world, often including drawings of the parts of a shark or ray that

are most useful for determining identification. Most such keys focus on ex-

ternal anatomy and the relative dimensions of body parts. For sharks, tooth

characteristics are extremely useful, as are fin size, shape, and location

(which is why we seldom get good identifications of attacking sharks; see

“Are sharks dangerous to people?” in chapter 9). Body proportions (depth

The Frilled Shark. Sometimes referred to as living fossils, Frilled Sharks are rare inhabitants of moderate depths
( 1 , 000 – 1 , 500 m, or 3 , 300 – 4 , 900 ft) and are considered to be among the most primitive of modern elasmobranchs
because of their tooth type, jaw connection to braincase, and six gill slits (placing them with the hexanchiform
cow sharks). Not seen alive in their natural habitat until 2004 , only a few have been filmed in the wild. The videos
show that Frilled Sharks have a very eel-like swimming motion, a behavior we would expect, given their long body
and short dorsal, anal, and pelvic fins set back near the tail. Wikimedia Commons, photo by Citron; http://en.wikipedia.org/wiki/
File:Chlamydoselachus_anguineus_head.jpg

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