Extinctions have been a natural part of the planet’s evolutionary history. 99% of the four billion species that have evolved on Earth are now gone. Most species have gone extinct.
Extinction may be defined as the termination of a lineage without issue or abrupt disappearance of specific groups of organisms without leaving descendents.Extinctions are of two types namely extinctions and pseudo extinction.In true extinctions a particular lineage totally disappears without any progeny or evolutionary descendents.
Pseudo extinction may also be called as phyletic extinction or phyletic transformation.In this type a group may disappear leaving descendents with evolutionary modifications.In horse evolution while the earliest ancestor Eohippus became extinct its descendent survived to produce the modern ‘Equus’.Extinctions can happen for the taxonomic groups such as a family or genus.Thus the extinction of dinosaurs as a group is a case of true extinction.Similar extinctions happened to tribolites.
The process of extinction is not always predetermined.It happens due to abrupt changes in environmental conditions or other biological factors.Through the use of computer models evolutionist can now examine the probability of extinction for large as well as small groups of organisms.From the fossil record it becomes that extinctions have occurred at regular intervals of time.
Pattern of extinction
Fossil record reveals a few patterns for extinction.Major groups of herbivorous vertebrates are more susceptible than the carnivorous vertebrates for extinction.Larger organisms easily became extinct.
Causes of extinction
Even though extinctions are regular events in the history of earth they are caused due to specific reasons
⭐A mass extinction may be due to drastic changes in the environmental conditions.
⭐Any adaptive advance in one species decreases the fitness of all other species.
⭐Over specialisation to a specific situation may cause extinction
⭐The spread of an epidemic disease without any control can cause extinction.
⭐An increase in the population strength of herbivorous animals can cause rapid food shortage and cause extinction for several inter related groups.
⭐A sudden cosmic radiation can cause the death of large organisms.
⭐A dust storm formed due to falling of a meteorite is commonly mentioned as a cause for the disappearance of dinosaurs.