''Macrorhineura'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of rhineurid

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

n or worm lizard, including the

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

and only species ''Macrorhineura skinneri'', named in 1970 on the basis of the front half of a skull from the

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...

Sharps Formation in

Wounded Knee, South Dakota Wounded Knee () is a census-designated place (CDP) on the Pine Ridge Indian Reservation in Oglala Lakota County, South Dakota, United States. The population was 364 at the 2020 census. The town is named for the Wounded Knee Creek which runs t ...

. Although the skull is incomplete, features such as a pointed, shovel-shaped snout indicate that it belongs to the family Rhineuridae. Within Rhineuridae, ''Macrorhineura'' is most closely related to '' Ototriton'' and '' Hyporhina'', two genera from the

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

and

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

of Colorado and Wyoming, based on the shared feature of equally sized

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

teeth in the lower jaw. Together they form a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

or evolutionary grouping of mid-continental rhineurids, which became isolated from a more western clade of rhineurids that includes ''

Dyticonastis ''Dyticonastis'' is an extinct genus of amphisbaenians, or worm lizards, that includes a single species, ''Dyticonastis rensbergeri'', that lived during the late Oligocene and early Miocene in what is now Oregon. Fossils of the species come from ...

'' and ''

Spathorhynchus ''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 Middle ...

''. Rhineurids were relatively common across much of North America during the

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

, but their range contracted in the

Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...

as the climate became colder, leaving only one living species in Florida, ''

Rhineura floridana ''Rhineura floridana'', known commonly as the Florida worm lizard, graveyard snake, or thunderworm, is a species of amphisbaenian in the family Rhineuridae. The species is the only extant member of the genus ''Rhineura'', and is found primarily ...

''. The presence of ''Macrorhineura'' in the Miocene shows that mid-continental rhineurids persisted into the Neogene, although by this time their distribution range was already shrinking.

References

Amphisbaenia Miocene lepidosaurs Miocene reptiles of North America Prehistoric lizard genera Fossil taxa described in 1970 {{paleo-lizard-stub