There are several different reasons why species become extinct. Sometimes extinctions are related to catastrophic global events such as the impact of a large comet or meteor, causing firestorms, great clouds of debris blotting out the sun, and so forth. Sometimes it is just a matter of natural selection as described by Darwin; species compete with other species, and some species lose the competition.
The dodo became an extinct species.
It means that there is no more left of that particular species. Like the dinosaurs became extinct, and stuff.
If an animal becomes extinct, there will be no more of that species left like the Dodo. No more are left as they are extinct.
None
The Quagga became extinct because they were easy to find and kill. They were over hunted and the species was not preserved.
Passenger pigeon, Carolina paraquet.
Florida manatees almost became extinct or died out completely
fossil record
Species die everyday , but new ones are discovered as well.
Quaggas were a species of zebra that lived in the plains of Africa. They became extinct partly because of being over hunted by Dutch settlers.
when there are no living members of a species the species is said to be "extinct".
If an animal in a ecosystem chain became extinct - the WHOLE ecosystem would collapse because, believe it or not, every single species counts. For example, if a bird species in a forest became extinct - everything that ate the bird would die without their "food" and everything that ate them would die and so on and so forth.