Rhineura (Worm Lizards), Lizards, and Earthworms

       

            Rhineura (worm lizards) and common lizards share a similarly shaped skull. They also share a common lizard ancestor, explaining the similarity in their skull shape. Worm lizards, however, have evolved using their skull to burrow underground and to spend most of its time moving and living underground. This has caused its skull to change slightly in structure to be harder.  Its life underground also accounts for the fact that the worm lizard is limbless and nearly blind.  Spending most of its time burrowing through the ground caused it to lose its limbs because they hindered its ability to burrow and caused it to lose its eyesight because it is not necessary to see when burrowing through dirt constantly.  A common lizard may use its skull to help it burrow but will also use its limbs to dig out a burrow and use it as a home.  It doesn’t live underground or move about under the ground like its relative the worm lizard.      

                             

                                                   

            They are both squamates and descended from the reptile lineage of lepidosaurs.  DNA studies have confirmed that they share a common lizard ancestor, which would explain their similarly shaped skulls and why the worm lizard has vestigial leg bones, indicating it was once four legged. 

            Worm lizards and earthworms look a lot alike.  They share an analogous trait of ring like scales that move to help them burrow underground.

                             

            Both the worm lizard and the earthworm primarily live underground, which explains the separate, but similar evolution in their ring like scales to help move them through the dirt.  Their scales move closer together, and then expand again to propel them through the ground.

 

            I think if we were able to pinpoint a distant common ancestor of both the worm lizard and the earthworm, it probably would have a similar ring like scale structure to help it burrow.  All life is theorized to have descended from one common ancestor, and during the earliest stages of the earth it is hypothesized that the earliest life forms were worm like and would burrow into the ground deep in the ocean.  With this in mind, I think it is entirely likely that burrowing worms in our earliest stages of evolution would carry this trait. 

            We can be sure that the worm lizard and the earthworm don’t have recent genetic ancestry because the earthworm is an invertebrate and the worm lizard is a vertebrate.  Earthworms don’t have bones, and worm lizards do have a skeletal structure.  Also, the lizard ancestor that the worm lizard can be traced back to had limbs and didn’t exhibit a ring like scale structure to live life primarily underground.  It seems that the worm lizard developed this trait for specific, burrowing purposes.