SHARKS - THE ADAPTABLE OLD-TIMERS
By Peter T. Pugliese and John Heinerman
Sharks are cartilaginous fish (i.e., having a skeleton wholly or largely composed of cartilage). They vary greatly ∈ size, behavior, and ∈ the way they reproduce. They are found at all depths ∈ all the oceans of the world except the Antarctic. However, they are most abundant ∈ tropical and subtropical waters. A few species of shark inhabit freshwater lakes and rivers, and some migrate regularly from salt to freshwater.
Sharks are remarkably successful animals, with few parasites or diseases and almost no enemies except other sharks. As predators and scavengers, sharks play a major role ∈ the ecosystems of the world‟s oceans.
Paleontologists believe that sharks evolved from some primitive, heavily armored, sluggish placoderm that became extinct about 350 million years ago, at the end of the Devonian era. This is approximately when the first shark-like creatures appeared. Sharks almost identical to those living today evolved about 160 million years ago, during the Jurassic period (same time period as represented ∈ the movie Jurassic Park). His species has survived unchanged for 160 million years. In contrast, we poor Homo Sapiens have been around for less than one million years.
Well-attuned to most of the waters of the world, sharks appear to dominate the depths. Swimmers, water skiers, snorkelers, scuba divers, and sea fishermen are invading their habitats ∈ ever-increasing numbers. Sharks have responded with predictable reflex reactions: they have attacked. The resulting notoriety has given sharks a bad reputation. The mass media have embellished the image, and now most people react with alarm to the word “shark”. However, the facts don‟t support this dread of sharks. Of the 100 or so unprovoked attacks that occur worldwide every year, fewer than 35 are fatal.
Internally, sharks are different than bony fish. Sharks have cartilaginous skeletons, skulls without sutures, no air ladder, and reserve rows of teeth attached to the skin of the jaws. Sharks‟ teeth are often found ∈ the wounds of those attacked. An abundance of fossil teeth does not necessarily indicate the presence of multitudes of sharks. Instead, it may indicate multitudes of teeth that were frequently lost and replaced.
From Devour Disease with shark liver oil. Green Bay: IMAKT, 1999.
According to the text, all the following are characteristics of sharks, EXCEPT
