Animal Extinction• Andrés Intriago• Mishell Ruiz• Rafael Chacán
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.
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. On the other hand, the average survival time for mammalian species over the past 20my has been 2.33my.
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...
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.
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 worlds 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.