It came at the cost of having no tail!
I’ve always wanted a prehensile tail. Maybe CRISPR can make that happen someday 😜
On a more serious note, it really bothers me when evolutionary biology articles say “this must have some advantage”, because that’s simply not how evolution works.
A trait can be absolute dogshit and still get passed around even with no advantage. It just depends how big the population is in the first place and how deadly the trait is. If it’s mostly benign, and the founding population isn’t huge, it’s going to persist regardless of usefulness. Especially if it’s a dominant expression.