Animal-lovers are shocked after a type of dolphin from China was declared extinct.
Human activities like too much fishing and pollution - are being blamed.
Dr Sam Turvey from the Zoological Society of London is an expert on animal extinctions past and present, as well as the creatures which are severely under threat.
He answered a selection of your questions:
Is it possible for an animal that is extinct to come back to life? - Hayleigh, 9, Edinburgh, Scotland
If an animal is extinct there aren't any left - they have all died.
It's very hard to tell if something is extinct because before an animal dies out it becomes very rare, so is difficult to find.
There is a chance there could be a few of the Yangtze River dolphins left, but it's very unlikely.
Some TV shows and films have featured dinosaurs coming back to life, but sadly scientists say it's impossible. Once they have died out, they are gone forever, which is a real tragedy.
What other animals are on the critically endangered list? - Amy, 12, Dublin, Ireland
Critically endangered animals are ones that are very, very close to dying out very soon. Animals are critically endangered all over the world because their forests are being destroyed or they are being hunted too much.
Also in the Yangtze River, other endangered animals include the Siberian Crane, the Chinese Alligator, the Chinese Paddle Fish and the Giant Salamander.
Are any other types of dolphins at risk? - Amy, 12, Bouillac, France
Sadly several other dolphins are in danger of dying out. The most highly threatened today is called the Vaquita. It's found in a very small part of Mexico and is threatened by being caught accidentally in fishing nets.
There may only be a handful left and we have to act now to help.
If China historically thinks this dolphin is a goddess, why did they not think to help it? - Erin, 11, London
For several years conservationists in China and around the world had hoped to try and catch some dolphins from the Yangtze and get them to breed in a large lake to save the species.
Sadly this plan was not carried out in time and we'll never know if it could of worked.
Can people do more to help endangered animals? - Shae, 7, Burnham-on-Sea, England
When you grow up you could try to become a conservationist to try and stop animals disappearing.
It's also important to talk about the animals with your friends and and family to try and raise awareness of them.