Extinct animals-mass extinction
herbivorous vertebrates are more susceptible than the carnivorous vertebrates for extinction. Larger organisms easily became extinct. VanValen(1973) recorded a constancy in the rate of extinction in a number of groups. He explained this using ‘Mac Arthor’s law’. According to this law as every new adaptation encourages the survival of a possessor it also decreases a fitness of other related species of that area.
Causes of extinction :- Even though extinctions are regular events in the history of earth they
are caused due to specific reasons (1) A mass extinction may be due to drastic changes in the environmental conditions. (2) Any adaptive advance in one species decreases the fitness of all other species. Thus according to Red Queen’s hypothesis you have to keep running pretty fast, just in order to stay in the same place. (3) Over specialistion to a specific situation may cause extinction.(ex. Antlers.) (4) The spread of an epidemic disease without any control can cause extinction. (5) An increase in the popuextinction for several inter-related groups. (6) A sudden cosmic radiation can
cause the death of large organisms. (7) A dust storm formed due to falling of a meteorite is commonly mentioned as a cause for the disappearance of dinosaurs. In the recorded history of earth, extinctions of major groups of organisms were due to natural causes. By the end of permian period of the Paleozoic Era, nearly 60% of the varieties then existed, became extinct. Similar large scale extinctions have been observed by the end of Mesozoic era and during Cenozoic time.
However the extintion of animals and plants during our time is mostly due to human interference. Thus the cause for the modern extinctions is invariably human acitivities. The realisation of a such a cause lead to starting of several international voluntary agencies to monitor and control extinctions. “The red-data book brought out regularly by W. W. F (World Wide Fund for nature, Formerly IUCN - International union for the conservation of nature and natural resources) provides a list of animals and plants that are endangered or have become extinct.