Possibly Shapeshifters??

I am desperately trying to find a book that meant a great deal to me when I was young, I forgot most of the details thinking I will always have the book but it got thrown away by a family member recently! I think it was called shapeshifters, was a child’s/young adults book, possibly written in the 70/80s. The front cover had a green border with foliage and possibly people on the front and/or a beach, possibly in the dark with black scales on it. It was about young adults that could shape shift. Not much to go on I know, but it would mean a lot to me if I could find it!

Could it have been a book from the animorphs series?