Where do you find a Ptera fossil on Fossil Fighters

You can get Ptera fossils only with Donation Points (DP). Each part will cost you 100 DP, but they'll always be rare fossils (red bones, they give you a 25 point bonus when you clean them). You get DP by cleaning a fossil rock you've cleaned before, and if it has a lower score than the one currently integrated/in storage, it gets donated. If you clean a fossil that's in storage (hasn't been revived yet), the fossil with the lower score will be donated. If you clean a fossil rock and get the same score as the fossil that's currently integrated/in storage, it gets donated.