Trafalgar Square Mammoth

If you bump into a woolly mammoth in Trafalgar Square today, it's in a good cause. London's Natural History Museum is displaying the replica as a warning about climate change, which made woolly mammoths extinct thousands of years ago. Can't say I'm dismayed that these giants aren't trampling around the UK nowadays. Imagine the mess they would make in my garden! The Yankee grey squirrel is bad enough. Question: If a species evolves into something new, can we truly say it has become extinct? If the woolly mammoth moved to Africa and shed it's fur to keep cool, the line didn't die out; it progressed. How can it be considered extinct if it's still going strong in a new, better adapted form?