The phrase "have been extinct" is grammatically correct and can be used in written English.
Example: Many scientists believe that dinosaurs have been extinct for millions of years.
Mountain lions have been extinct in New England for decades".
Everyone knows that ordinary wolves have been extinct in Ireland for centuries.
The animals have also recolonised parts of Scandinavia and the UK where they have been extinct for centuries.
Before Ms. Courtenay-Latimer's discovery, the coelacanth was thought to have been extinct for at least 70 million years.
But humans, chimps, mice, and rats are all living organisms, while Neanderthals have been extinct for thirty thousand years.
A water vole prior to release on the Holnicote Estate, Somerset, where the mammals have been extinct for 30 years.
They've been extinct for millions of years!
Both were part of a project to reintroduce bears to areas of Europe where they had been extinct.
A six-ton carnivore with teeth the size of bananas is bound to make the news even if that animal has been extinct for 65 million years.
Using such techniques, researchers have now resurrected the DNA of the Tasmanian tiger, the world's largest carnivorous marsupial, which has been extinct for more than seventy years.
