Ball python skeleton by Jean-Christophe Theil
For example, I’ve been surprised to learn that many people don’t realize that snakes are vertebrates like us. They have a spine & skeleton just like us, dogs, cats, frogs, giraffes, etc. In fact, it might surprise you to learn that snakes are still classified as tetrapods… four-limbed animals!
Though snake skeletons have been radically adapted to their long, streamlined body form, they are still considered highly-specialized lizards in the order squamata. Instead of tens of vertebrae & ribs, they have hundreds, each set of ribs enveloped by a band of muscle which gives them incredible control over every inch of their body. Their bones are more flexible than ours, allowing them to squeeze into tight spaces, but their bones are also thinner and more fragile, so we take extra care while handling them.
Wilson the Ball Python
The fragility of snake skeletons has an unfortunate impact on their fossil-record. The only largely complete snake fossils that survive today are almost entirely marine deposits where the skeleton is preserved in the soft silt & mud of the sea floor. Most terrestrial fossils are isolated partial jaws or vertebrae, thus, the mystery surrounding the evolution of snakes is a matter still hotly debated to this day. While palaeontologists haven’t yet discovered a true 4-legged snake fossil, we do have fossils of snake ancestors with intact hind limbs & pelvises (eg: Pachyrhachis), and extant “primitive” species, like boas & pythons, still have the vestigial remains of a femur & pelvis including a tiny external “claw” or “pelvic spur” on either side of their cloaca.
