2. Extinction is one of the major features of
evolution. A species is extinct when no members
of the species are still alive.
All species become extinct sooner or later. The
end of a species may happen for many reasons.
It may be caused by habitat loss or by being
overhunted, or by a major extinction event. An
example of an animal that is now extinct is the
Dodo, from over-hunting.
A species that is endangered has a good chance
of becoming extinct. Fossil species sometimes
reappear millions of years after they were thought
to be extinct. These cases are called Lazarus
taxa.
3. Duration of species
The average duration of species varies according
to the groups studied. A study of benthic (deep
water) foraminifera showed an average of 16
million years if they lived above 200 metres, but
25my if they lived below 200 metres.[2] On the
other hand, the average survival time for
mammalian species over the past 20my has been
2.33my.
4. Duration of higher groups
Naturally, higher categories such as genera,
families, orders, classes and phyla last longer,
because they are composed of more species. As
far as we know, no phylum has gone completely
extinct since the Cambrian, but quite a few
classes went extinct in one or other of the 'big
five' extinction events. Examples of higher
categories of animal now extinct are: placoderm
fish, trilobites, ammonites, pelycosaurs,
dinosaurs, pterosaurs, ichthyosaurs,
plesiosaurs...
5. Reasons
Darwin thought that most extinctions occurred
because some organisms became more effective,
and replaced their less advanced competitors. No
doubt that does occur. But now we put more
emphasis on environmental changes. Organisms
become adapted to the environments they live it.
The environment certainly does change, and
sometimes quite dramatically. When it does,
some organisms can adapt to the changes, and
some cannot. The ones that cannot become
extinct. That is all there is to it.
6. Galapagos Animals
The Galapagos animals are perhaps the most
famous attractions of this archipelago. The
animals of the Galapagos Island are most notable
for their uniqueness and their proximity to visitors.
Visitors can literally swim and hike right alongside
some of the world's most unique species, as they
exist in their natural habitat. Some of the most
popular endemic Galapagos animals are close to
extinction, and their protection is of high priority.
As such, it is best to observe the rules
surrounding a visit to the Galapagos Islands to
ensure the safety of Galapagos animals for years
to come.
