Old art reuploaded from DA, Apr 2020

A celebration of the convergent evolution of sail-like back structures in vertebrates, starring Dimetrodon, Arizonasaurus, and Spinosaurus. I believe this was right before the new Spinosaurus papers began to come out, so that's my excuse for the spino here.
I know I could have included Edaphosaurus, Platyhistrix, Ouranosaurus, and more. I didn't want to.