How the Snake Lost Its Legs

How the Snake Lost Its Legs

In the article "How the Snake Lost Its Legs," Carl Zimmer wrote about the common theory of snake evolution is about to be questioned. All vertebrates that live on land whether mammalian or reptilian are known as tetrapods. In most animals these feet evolved into other limbs, like arms for humans and into wings for birds; however, the snake lost its four feet altogether. The only sign that snakes ever had four feet is a remaining hip located within the rib cage. Paleontologists and herpetologists alike find it difficult to retrace the ancestry of snakes. Because of their scales, eggs, and subtle features of the skull, some scientists believe that snakes are descendants of lizards. However, this still does not explain how snakes lost their legs.

In 1970, a three-foot-long creature, Pachyrachis Problematicus, was discovered near Jerusalem. A Hebrew University herpetologist studied the fossil and suggested that even though the animal looked serpentine there was not enough evidence supporting the theory that it was related to snakes. In 1996, Michael Lee and Michael Caldwell studied the fossil more thoroughly. Lee stated that "The first thing that you've got to do is look at every possible animal it could be related to", he and Caldwell concluded that the Pachyrachis had many snake like characteristics.(Zimmer p.32) For example, "the body is long and sinuous: it has 140 vertebrae in its trunk; most lizards have just 25."(Zimmer p.32) Lizards have open brain cavities while snakes are completely sealed. The jaws of Pachyrachis are very flexible and the lower jaw does not fuse to the chin. The fossil has two hind legs about an inch long each; they are not attached to feet. While the feet could have washed away Lee and Caldwell believe that the feet were vestigial if anything. The hips unlike modern snakes were on the outside of the ribcage. A holistic view of Pachyrachis' traits show the modern snake to be related to a large marine lizard called a Mosasaur. "Mosasaurs began as four-legged lizards on land."(Zimmer p.32) As the mosasaur took to water their