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cluding fish, arose. Today there are
over 24 000 different types of fish
(some of the latest estimates place
this figure close to 30 000) all descended from the ancient fishlike
creatures of the middle Ordovician
period about 480 million years ago.
Over time some have evolved into
weird and wonderful shapes and
colours to the extent that they now
hardly look like fish at all. Others,
however, have remained virtually
unchanged. They are the so-called
“living fossils” the most famous of
which are undoubtedly the coelacanths, whose present-day representatives are almost identical to the
last fossils known from deposits da-
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ting back some 70 million years.
Fish are remarkable creatures. During
the course of evolution they have
developed physical and behavioural
characteristics that have allowed
them to inhabit most of the world’s
bodies of water, except for a few
places where no life can possibly exist. They have spread to such diverse
habitats as coral reefs, dark abysses,
deep caves, thermal springs, arctic
waters, seasonal pools, raging torrents, mid-ocean expanses, and numerous other watery worlds. As a
result, the forces of evolution have
moulded fish into myriad configurations that make it possible for them
not just to tolerate such conditions
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but to thrive and breed in them, often in spectacular ways.
Fish Evolution:
It is generally accepted that life began in water some 3 billion years
ago. For many millions of years after
that there appears to have been no
major development leading to the
emergence of complex organisms.
Indeed, it took around 2.4 billion
years before the first animals that
could be regarded as invertebrates
began to evolve. From then on the
pace accelerated, and it only took a
relatively short time of about 120
million years before the first vertebrates evolved. These aquatic creatures, known from fossils dating
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