Rhineuridae is a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

amphisbaenia Amphisbaenia (called amphisbaenians or worm lizards) is a group of usually legless squamates, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. As ...

ns (commonly called worm lizards) that includes one living

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

and

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

, ''

Rhineura floridana ''Rhineura floridana'', known commonly as the Florida worm lizard, graveyard snake, Goin CJ, Goin OB, Zug GR (1978). ''Introduction to Herpetology, Third Edition''. San Francisco: W.H. Freeman and Company. xi + 378 pp. . (''Rhineura floridana ...

'', as well as many extinct species belonging to both ''Rhineura'' and several extinct genera. The living ''R. floridana'' is found only in

Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...

and

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...

, but extinct species ranged across North America, some occurring as far west as Oregon. The family has a fossil record stretching back 60 million years to the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pala ...

and was most diverse in the continental interior during the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

and

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...

Fossil record

The fossil record of the Rhineuridae extends back almost to the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

, with the oldest rhineurid, '' Plesiorhineura tsentasai'', occurring in the Early Paleocene. ''Plesiorhineura'' is only known from a partial jaw, but it shares many features with modern rhineurids. Eocene rhineurids, such as ''

Spathorhynchus fossorium ''Spathorhynchus'' is an extinct genus of amphisbaenians or worm lizards that existed from the Middle Eocene to the Early Oligocene in what is now Wyoming. It includes two species, the type species ''S. fossorium'', named in 1973 from the Midd ...

'', are remarkably similar to the modern ''Rhineura'', suggesting very conservative evolution within the family. Unlike the

Amphisbaenidae The Amphisbaenidae (common name: worm lizards) are a family of amphisbaenians, a group of limbless vertebrates. Geographic range Amphisbaenids occur in South America, some Caribbean islands, Europe, and sub-Saharan Africa. Taxonomy One deep- ...

, which include round-headed, keeled, and shovel-snouted forms, the fossil rhineurids are exclusively of the shovel-snouted variety. The fossil rhineurids are known exclusively from North America, but show that the group once had a much wider distribution than the current range of ''R. floridana'', with species known from Colorado, Wyoming, South Dakota, Montana, and as far west as Oregon.Berman, David S. "A new amphisbaenian (Reptilia: Amphisbaenia) from the Oligocene-Miocene John Day formation, Oregon." Journal of Paleontology (1976): 165-174. The wide distribution probably reflects the fact that the climate was much warmer in the past. The initial rhineurid radiation in North America occurred when most of the continent was humid and subtropical. Rhineurids persisted through a significant climatic transition around the time of the Eocene-Oligocene boundary in which most of North America became semi-arid and covered by

savanna A savanna or savannah is a mixed woodland- grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground ...

s. The decline of rhineurids began with an abrupt period of cooling called Middle Miocene disruption. The distribution range of rhineurids shrank southward as global temperatures continued to fall, leaving ''R. floridana'' isolated in Florida as the only living representative of the group. In 2007, paleontologist Daniel Hembree reviewed all North American fossil amphisbaenians and found every species to belong to Rhineuridae. He also showed that many extinct rhineurids cannot be justified as their own species and are instead

synonyms A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are ...

of earlier named species, reducing the number of valid species from twenty-two to nine. For example, ''Jepsibaena minor'', ''Rhineura amblyceps'', ''R. attenuatus'' ''R. minutus'', and ''R. wilsoni'' are sometimes considered synonyms of '' Protorhineura hatchetri''. Since the late nineteenth century, paleontologists had been naming new species of extinct North American amphisbaenians on the basis of single fragmentary specimens that often preserved too few anatomical features to support their status as distinct species. By synonymizing many of these species, Hembree showed that rhineurid diversity in North America was lower than once thought.

Relationships

Hebree's 2007 review of North American amphisbaenians also included a

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

of rhineurids and other amphisbaenian lizards. The analysis found that ''Rhineura floridana'' is the most basal species within the family, meaning its lineage was the first to diverge from the group. However, the species itself is quite young, with the oldest fossils coming from the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

of Florida. The ancestor of ''R. floridana'' likely migrated into what is now Florida from the continental interior, while the remaining rhineurids remained there to radiate and diversify.

References

{{Taxonbar, from=Q13416851 Amphisbaenians Reptiles of the United States Natural history of Florida Lizard families Taxa named by Paulo Vanzolini Extant Paleocene first appearances