Ask the Experts: How do you know the animals are extinct?

This is a very interesting question - how can we be sure that an animal is really extinct? How do we know there aren't still some lost mammoths - or even dinosaurs - hidden in a Lost World in some remote corner of the globe? Well, the most honest answer is we really can't ever be totally sure - but we can say that the chances of a species surviving are so amazingly slim that it would be virtually impossible to find one remaining.

That's not to say it still can't happen, though - and in fact it has, several times! Famously, in 1938, fishermen off the east coast of Africa caught a kind of fish, called a coelacanth, that scientists had thought went extinct with the dinosaurs. Other animals, like a certain type of ant and a certain type of shellfish, as well as several types of plants, have also been rediscovered by science after they were presumed long extinct. When a species or group reappears after disappearing from the fossil record for a long period, scientists call it a Lazarus taxon.

Still, its one thing to rediscover a type of ant, and another to rediscover a 12,000 pound mammoth. It might be possible to hide from scientists and explorers in the far recesses of inaccessible rainforest, or down in the deepest depths of the ocean, but mastodons and giant sloths roamed the same hills and plains and woodlands that humans visit and inhabit.

If they still exist somewhere, where is the evidence of them? Why do we suddenly stop finding bones and other evidence of Ice Age mammals at the end of the Pleistocene? Where could they have been hiding for the last 12,000 years? Even the very last mammoth bones we see anywhere on Earth, from remote and sheltered Wrangel Island in Siberia, are still at least 4000 years old - and those mammoths only managed to survive that long by changing dramatically.

In short, it always may be possible to discover a member of some Lost World in the remote Arctic or at the bottom of the sea. But the larger the animal, the less remote its natural habitat, and the longer its been since we stop finding evidence of it, the more certain we can be that it really has gone extinct.

DJ