Evolution and systematics

Most recent phylogenetic analyses have placed amphis-baenians as one of three suborders of Squamates (the clade that includes snakes, lizards, and amphisbaenians), but their exact placement within that clade is not well understood. The interrelationships among the four amphisbaenian families are also poorly understood. Past studies disagree on whether rhineurids are the most primitive amphisbaenians or are derived within the group. A recent phylogenetic analysis suggests that rhineurids are derived amphisbaenians.

The family Rhineuridae is the only amphisbaenian family with a significant fossil record. This fossil record is entirely from the western and central United States, indicating that rhineurids were once widely distributed across the United States, whereas today a single relict species occurs in Florida. Rhineurids are found in the fossil record extending as far back as the Paleocene (about 60 million years ago). These fossils are already quite derived, exhibiting a shovel-headed cranial shape similar to that occurring in the extant species from Florida, but they also exhibit some intriguing primitive cranial features that are absent in most amphisbaenian species living today. For example, some fossil rhineurids have a complete orbit, enclosed posteriorly by the jugal bone, an element of the skull that is absent in all extant forms. The presence or absence of limbs in these fossil forms is not definitively known due to vagaries of fossil preservation, but no limb elements have been found so far associated with these fossils. If rhineurid fossils are ever found with preserved limb elements, this would significantly change our understanding of relationships within Amphisbaenia.

Florida wormlizard (Rhineura floridana). (Illustration by John Megahan)
A Florida wormlizard (Rhineura floridana). (Photo by Dave Norris/Photo Researchers, Inc. Reproduced by permission.)

The taxonomy of this species is Rhineura floridana Baird, 1859, Micanopy, Florida.

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