Amphisbaenia 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. As many species have a pink body and scales arranged in rings, they have a superficial resemblance to earthworms. While the genus Bipes retains forelimbs, all other genera are limbless. Recent phylogenetic studies suggest that they are nested within Lacertoidea, closed related to the lizard family Lacertidae. Amphisbaenians are widely distributed, occurring in North America, Europe, Africa, South America, Western Asia and the Caribbean. Most species are less than 6 inches (15 cm) long.
The Lacertidae are the family of the wall lizards, true lizards, or sometimes simply lacertas, which are native to Afro-Eurasia. It is a diverse family with at about 360 species in 39 genera. They represent the dominant group of reptiles found in Europe.
Peltosaurus is an extinct genus of anguid lizard from North America that lived from the Eocene to the Oligocene. Peltosaurus belongs to the anguid subfamily Glyptosaurinae. The type species Peltosaurus granulosus was named in 1873 by American paleontologist Edward Drinker Cope. Many additional species have been named, but most have been reassigned to different genera. For example, Peltosaurus piger, named in 1928, was reclassified as Odaxosaurus piger, and P. jepseni, named in 1942 from the Paleocene of Wyoming, but was later reclassified as Proxestops jepseni. In 1955 a new species, Peltosaurus macrodon, was named from the Eocene of California. Lizard bones from the Late Miocene of Nebraska were attributed to a new species of Peltosaurus called P. minimus in 1976, extending the fossil range of Peltosaurus and Glyptosaurinae into the Neogene. However, these bones were later referred to a genus of skinks called Eumeces, meaning that the fossil range of Peltosaurus and Glyptosaurinae does not go beyond the Paleogene.
The John Day Formation is a series of rock strata exposed in the Picture Gorge district of the John Day River basin and elsewhere in north-central Oregon in the United States. The Picture Gorge exposure lies east of the Blue Mountain uplift, which cuts southwest–northeast through the Horse Heaven mining district northeast of Madras. Aside from the Picture Gorge district, which defines the type, the formation is visible on the surface in two other areas: another exposure is in the Warm Springs district west of the uplift, between it and the Cascade Range, and the third is along the south side of the Ochoco Mountains. All three exposures, consisting mainly of tuffaceous sediments and pyroclastic rock rich in silica, lie unconformably between the older rocks of the Clarno Formation below and Columbia River basalts above.
Rhineura is a genus of worm lizard endemic to North America. The genus has only one extant species but more are known from fossil record. They are also known as the North American worm lizards.
Lazarussuchus is an extinct genus of amphibious reptile, known from the Cenozoic of Europe. It is the youngest known member of Choristodera, an extinct order of aquatic reptiles that first appeared in the Middle Jurassic. Fossils have been found in Late Paleocene, Late Oligocene, Early Miocene and possibly Late Miocene deposits in France, Germany, and the Czech Republic. Two species have been named: the type species L. inexpectatus ("unexpected") from the late Oligocene of France. and L. dvoraki from the early Miocene of the Czech Republic. It was not a large animal; with the total preserved body and tail length of L. inexpectatus being just over 30 centimetres. A complete specimen of Lazarussuchus with preserved soft tissue was found from the Late Paleocene of France, but has not been assigned to a species.
Herpetotheriidae is an extinct family of metatherians, closely related to marsupials. Species of this family are generally reconstructed as terrestrial, and are considered morphologically similar to modern opossums. Fossils of herpetotheriids come from North America, Asia, Europe, Africa, and perhaps South America. The oldest representative is Maastrichtidelphys from the latest Cretaceous (Maastrichtian) of the Netherlands and the youngest member is Amphiperatherium from the Middle Miocene of Europe. The group has been suggested to be paraphyletic, with an analysis of petrosal anatomy finding that North American Herpetotherium was more closely related to marsupials than the European Peratherium and Amphiperatherium.
Archaeohippus is an extinct three toed member of the family Equidae known from fossils of early Oligocene to middle Miocene age. The genus is noted for several distinct skeletal features. The skull possesses deeply pocketed fossa in a notably long preorbital region. The genus is considered an example of phyletic dwarfism with adults estimated at being on average 20kg in weight. This is in contrast to the most common equid of the period, Miohippus. Characters of the teeth show a mix of both primitive and advanced traits. The advanced traits are very similar to those shown in the genus Parahippus. The noted similarities of Archaeohippus and Parahippus show them to be descended from a common ancestor and are considered sister species.
Orthogenysuchus is an extinct genus of caimanine alligatorids. Fossils have been found from the Wasatch Beds of the Willwood Formation of Wyoming, deposited during the early Eocene. The type species is O. olseni. The holotype, known as AMNH 5178, is the only known specimen belonging to the genus and consists of a skull lacking the lower jaws. The braincase is filled in by the matrix and most of the suture lines between bones are indiscernible, making comparisons with other eusuchian material difficult.
Thecachampsa is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from the eastern United States in deposits of Miocene age. Those named in the 19th century were distinguished primarily by the shape of their teeth, and have since been combined with T. antiquus. More recently erected species were reassigned from other genera, although their assignment to Thecachampsa has since been questioned.
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 the John Day Formation. It belongs to Rhineuridae, a family that includes many other extinct North American amphisbaenians but only one living species, Rhineura floridana, from Florida. Dyticonastis rensbergeri occurs the farthest west of all rhineurid species. Like all rhineurids, Dyticonastis has a shovel-like snout adapted for burrowing underground, but it differs from most other members of the group in having a relatively shallow angle to its snout wedge and in having a widened snout tip. The only other rhineurids that share these features are species of the genus Spathorhynchus, which lived from the Middle Eocene to the Early Oligocene in what is now Wyoming. A 2007, phylogenetic analysis of amphisbaenians found that Dyticonastis and Spathorhynchus are each other's closest relatives, suggesting that both taxa may have evolved through vicariant speciation; the growth of the Rocky Mountains during the earliest stages of the Laramide orogeny in the early Paleogene would have separated North American rhineurids into eastern and western populations, with the western population producing Dyticonastis 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 Eocene Bridger and Wind River Formations, and the species S. natronicus, named in 1977 from the Lower Oligocene White River Formation. Spathorhynchus belongs to the family Rhineuridae, which includes many other extinct species that ranged across North America at various times in the Cenozoic but only has one surviving member, Rhineura floridana, from Florida. Spathorhynchus differs from all other rhineurids except Dyticonastis from the Late Oligocene-Early Miocene of Oregon in having a slightly widened, spatula-shaped snout tip with a low angle of about 30 degrees. The two taxa may be closely related, having evolved in isolation in western North America after the formation of the Rocky Mountains separated them from rhineurids further east.
Ototriton is an extinct genus of rhineurid amphisbaenian or worm lizard from the Early Eocene of the western United States, including the type and only species Ototriton solidus. Paleontologist F. B. Loomis named Ototriton in 1919 on the basis of a single skull from the Wind River Formation in Wyoming, misinterpreting it as the skull of a salamander. Unlike salamanders and like other rhineurids, Ototriton has a shovel-shaped snout that it presumably used for burrowing underground. Ototriton is one of the earliest known rhineurids and also one of the largest.
Macrorhineura is an extinct genus of rhineurid amphisbaenian or worm lizard, including the type and only species Macrorhineura skinneri, named in 1970 on the basis of the front half of a skull from the Early Miocene Sharps Formation in Wounded Knee, South Dakota. 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 and Oligocene of Colorado and Wyoming, based on the shared feature of equally sized dentary teeth in the lower jaw. Together they form a clade or evolutionary grouping of mid-continental rhineurids, which became isolated from a more western clade of rhineurids that includes Dyticonastis and Spathorhynchus. Rhineurids were relatively common across much of North America during the Paleogene, but their range contracted in the Neogene as the climate became colder, leaving only one living species in Florida, Rhineura floridana. 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.
Hyporhina is an extinct genus of amphisbaenians or worm lizards that lived from the Late Eocene to the Middle Oligocene in what is now the western United States.
The Sharps Formation is a geologic formation in South Dakota. It preserves fossils dating back to the Paleogene.
The Wind River Formation is a geologic formation in Wyoming in the Wind River Basin. It preserves fossils dating back to the Paleogene period. A recent study by Stanford suggests that fracking has contaminated the entire ground water resource in the basin.
Archaerhineura was a genus of amphisbaenian lizards in the family Rhineuridae that is now extinct. The only species is Archaerhineura mephitis, named in 2015 on the basis of a single fragment of the lower jaw from the Polecat Bench Formation in Park County, Wyoming, which dates to the late Paleocene. Archaerhineura is one of the oldest amphisbaenians and was part of an evolutionary radiation of Rhineuridae in the Paleocene several million years after the Cretaceous–Paleogene extinction event. This rhineurid radiation coincided with the radiation of another group of amphisbaenians, Amphisbaeniformes, which includes the still-extant families Blanidae and Amphisbaenidae. The presence of Archaerhineura and other Paleocene rhineurids in the western United States indicates that amphisbaenians, which would later have a nearly global distribution, originated in North America.
Chthonophis is an extinct genus of amphisbaenian lizard with only one known species, Chthonophis subterraneus, from the earliest Paleocene of northeastern Montana. Chthonophis was named in 2015 on the basis of a partial lower jaw from an outcrop of the Fort Union Formation in the Bug Creek Anthills. The surfaces of the bone are well-rounded, suggesting that the remains had been partially digested by another animal before the jaw had been buried and fossilized. Chthonophis is the oldest known amphisbaenian, yet phylogenetic analysis shows that it was not the most basal. Longrich et al. (2015) classified Chthonophis in its own family, Chthonophidae, finding it to be more derived than Rhineuridae but more basal than other clades such as Blanidae and Amphisbaenidae. The existence of a derived amphisbaenian soon after the Cretaceous-Paleogene extinction event suggests that Amphisbaenia has its origins in the Cretaceous, although no Cretaceous amphisbaenians are currently known. Below is a cladogram from Longrich et al. (2015) showing the phylogenetic relationships of Chthonophis:
Anniealexandria is an extinct genus of amphisbaenian lizard known by the type species Anniealexandria gansi from the earliest Eocene of Wyoming. Anniealexandria is the only known member of the family Bipedidae in the fossil record, which otherwise only includes the extant genus Bipes from Mexico. It was named in 2009 in honor of Annie Montague Alexander, founder of the University of California Museum of Paleontology. Remains of Anniealexandria are known only from a single fossil locality in the Bighorn Basin called Castle Gardens, but within the locality its fossils are common in the Willwood Formation, usually consisting of isolated jaw bones and vertebrae. Anniealexandria seems to have been a common component of a paleofauna that included fifteen other lizard species and existed in western North America during a period of global warming in the latest Paleocene and earliest Eocene.
