A zygosphene is a median process on the front part of the neural arch of the vertebrae of most snakes and some lizards.

A zygantrum is a cavity on the vertebrae of snakes and some lizards which helps fit a pivot joint called a zygosphene inside each vertebra.

Yes, reptile have vertebrae. Snakes have especially distinctive vertebrae as they are the only animal to have a zygosphene and zygantrum, to keep the adjacent vertebrae from twisting. Turtles are also distinctive as most are fused to the carapace.

There are many differences but the most easily distinguished bones are the vertebra. In reptiles, the concave part of the centrum faces the anterior, while in mammals and other animals it always faces posterior. Snake vertebra are also easy to distinguish from other reptiles and mammals because of the presence of the zygosphene and zygantrum. These are articular processes on either side of the snake vert that keep the vertebral column from twisting side-to-side. These processes are not present in any other animal's vertebrae. There are also obvious differences, such as the bony elements of the turtle shell that can differentiate mammal from reptile.