You can't. But its tooth is proof enough that it is an unknown species.
Yes, you can find proof of The Jersey Devil, Bigfoot, Nessie, and the Chupacabra. (see related question)
When you first start the island and you get the paper about Mews needing the evidence of ONE cryptid to get your reward, you end up needing to search for 4: Bigfoot, the Loch Ness Monster, the Chupacabra, and the Jersey Devil.
you find the chupacabra in puerto rico. you have too gather 3 spotted goats were the huge bones are then just wait and see
You need a photo of the actual Nessie, a tooth from the chupacabra, and egg shells from the Jersey Devil. (see the related questions below)
There are 3 you have to prove: Nessie (Loch Ness) Chupacabra (Puerto Rico) New Jersey Devil (New Jersey) You can't get what you need to prove the Yeti, so you are sent to find Bigfoot.
On your first visit to Puerto Rico, you find some fur that turns out to be a dog's fur. On your second trip, the farmer is out to capture the chupacabra. You will find him at Snaggletooth Rock in the center of the map. Use your jeep to herd 3 of the spotted goats into the area (as bait), then join the farmer at the rock. He has a crate set up to trap the creature, but it escapes, and fortunately loses a tooth for you to bring back to Mews.
To win the island, you must find the proof that confirms the existence of three legendary cryptids : Nessie of Loch Ness, the Chupacabra, and the Jersey Devil. Then you have to rescue the 4th creature, Bigfoot, from the evil plans of Gretchen Grimlock. (see related solution question)
You will search for evidence in four locations around the globe where cryptids have been observed. As you discover possible clues, you examine them to see if they are genuine. Nessie - at Loch Ness Yeti - in the Himalayas Chupacabra - in Puerto Rico Jersey Devil - in New Jersey (see solution at the related question)
Prove 4 cryptids to qualify for the Mews million-dollar reward. You find a footprint that may be from the Yeti, but you can only prove Nessie, the Chupacabra, and the New Jersey Devil. Then you have to track Bigfoot and save him from Gretchen Grimlock. (see the related solution question)
You don't. Gte the lantern from the monastery, and take a photo of the footprint in the snow. But Mews is not convinced so you don't go back. Instead, once you have proved the other three cryptids (Nessie, chupacabra, and Jersey Devil), he sends you to hunt Bigfoot, who is similar to the Yeti.
Since the monks won't let you test the Yeti scalp, you have no proof. Once you have the lantern and the footprint photo, you can find nothing at the Himalayas. However, once you prove the other three cryptids (Nessie, Chupacabra, and the Jersey Devil), Mews will send you in pursuit of the similar creature, Bigfoot.
In the monastery.