Lysorophia is an order of fossorial Carboniferous and Permian tetrapods within the Recumbirostra. Lysorophians resembled small snakes, as their bodies are extremely elongate. There is a single family, the Molgophidae. Currently there are around five genera included within Lysorophia, although many may not be valid.
Adelospondyli is an order of elongated, presumably aquatic, Carboniferous amphibians. They have a robust skull roofed with solid bone, and orbits located towards the front of the skull. The limbs were almost certainly absent, although some historical sources reported them to be present. Despite the likely absence of limbs, adelospondyls retained a large part of the bony shoulder girdle. Adelospondyls have been assigned to a variety of groups in the past. They have traditionally been seen as members of the subclass Lepospondyli, related to other unusual early tetrapods such as "microsaurs", "nectrideans", and aïstopods. Analyses such as Ruta & Coates (2007) have offered an alternate classification scheme, arguing that adelospondyls were actually far removed from other lepospondyls, instead being stem-tetrapod stegocephalians closely related to the family Colosteidae.
Aistopoda is an order of highly specialised snake-like stegocephalians known from the Carboniferous and Early Permian of Europe and North America, ranging from tiny forms only 5 centimetres (2 in), to nearly 1 metre (3.3 ft) in length. They first appear in the fossil record in the Mississippian period and continue through to the Early Permian.
Lethiscus is the earliest known representative of the Aistopoda, a group of very specialised snake-like tetrapodomorphs known from the early Carboniferous (Mississippian).
Hanssuesia is a genus of pachycephalosaurid dinosaurs from the late Cretaceous period. It lived in what is now Alberta and Montana, and contains the single species Hanssuesia sternbergi.
Pachyrhachis is an extinct genus of snake with well developed hind legs known from fossils discovered in Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively small snake, measuring more than 1.5 metres (4.9 ft) long at maximum. Pachyrhachis appears to have been an ancient marine snake; the fossils occur in a marine limestone deposit, and the thickened bone of the ribs and vertebrae would have functioned as ballast to decrease the buoyancy of the animal, allowing it to dive beneath the ancient Cretaceous seas that it once inhabited.
Ophiderpeton is an extinct genus of aistopod tetrapodomorphs from the early Carboniferous to the early Permian. Remains of this genus are widespread and were found in Ohio, United States, Ireland, and the Czech Republic.
Phlegethontia is an extinct genus of aïstopod tetrapodomorphs from the Carboniferous and Permian periods of Europe and North America.
Nectridea is the name of an extinct order of lepospondyl tetrapods from the Carboniferous and Permian periods, including animals such as Diplocaulus. In appearance, they would have resembled modern newts or aquatic salamanders, although they are not close relatives of modern amphibians. They were characterized by long, flattened tails to aid in swimming, as well as numerous features of the vertebrae.
Coloraderpeton is an extinct genus of aïstopod tetrapodomorphs within the family Oestocephalidae. Coloraderpeton is known from the Carboniferous Sangre de Cristo Formation of Colorado, and was initially known from vertebrae, ribs, and scales recovered from a UCLA field expedition in 1966. Peter Paul Vaughn described these remains in 1969. A skull was later reported in an unpublished 1983 thesis and formally described by Jason S. Anderson in 2003.
Limnerpeton is an extinct genus of dissorophoidean euskelian temnospondyl within the family Amphibamidae.
Oestocephalus is an extinct genus of aïstopod tetrapodomorphs that lived during the Carboniferous period. Fossils have been found in the Czech Republic, and in Ohio and Illinois in the United States. It is the type genus of the family Oestocephalidae, although it used to be assigned to the family Ophiderpetontidae, which is now considered paraphyletic. It was named by Edward Drinker Cope in 1868 and now contains two species, O. amphiuminus and O. nanum.
Rhynchonkos is an extinct genus of rhynchonkid microsaur. Originally known as Goniorhynchus, it was renamed in 1981 because the name had already been given to another genus; the family, likewise, was originally named Goniorhynchidae but renamed in 1988. The type and only known species is R. stovalli, found from the Early Permian Fairmont Shale in Cleveland County, Oklahoma. Rhynchonkos shares many similarities with Eocaecilia, an early caecilian from the Early Jurassic of Arizona. Similarities between Rhynchonkos and Eocaecilia have been taken as evidence that caecilians are descendants of microsaurs. However, such a relationship is no longer widely accepted.
Pseudophlegethontia is an extinct genus of aïstopod tetrapodomorphs. It is the only member of the family Pseudophlegethontiidae. The only species is the type species P. turnbullorum, named in 2003. Fossils of Pseudophlegethontia have been found from the Mazon Creek fossil beds in Grundy County, Illinois, a conservation lagerstätte well known for the exceptional preservation of middle Pennsylvanian taxa.
Utaherpeton is an extinct genus of lepospondyl amphibian from the Carboniferous of Utah. It is one of the oldest and possibly one of the most basal ("primitive") known lepospondyls. The genus is monotypic, including only the type species Utaherpeton franklini. Utaherpeton was named in 1991 from the Manning Canyon Shale Formation, which dates to the Mississippian-Pennsylvanian boundary. It was originally classified within Microsauria, a group of superficially lizard- and salamander-like lepospondyls that is now no longer considered to be a valid clade or evolutionary grouping, but rather an evolutionary grade consisting of the most basal lepospondyls. Utaherpeton has been proposed as both the most basal lepospondyl and the oldest "microsaur", although more derived lepospondyls are known from earlier in the Carboniferous. However, its position within Lepospondyli remains uncertain due to the incomplete preservation of the only known specimen. The inclusion of Utaherpeton in various phylogenetic analyses has resulted in multiple phylogenies that are very different from one another, making it a significant taxon in terms of understanding the interrelationships of lepospondyls.
Sillerpeton is an extinct genus of aïstopod tetrapodomorphs within the family Phlegethontiidae. It contains a single species, Sillerpeton permianum, which is based on braincases and vertebrae from the Early Permian Richards Spur locality of Oklahoma.
Holospondyli is a proposed clade of lepospondyls from the Early Carboniferous to the Late Permian that includes the aistopods, the paraphyletic nectrideans, and possibly also Adelospondyli. However, aistopods have since been recovered as stem-tetrapods more primitive than temnospondyls or other groups of lepospondyls.
Phlegethontioidea is a clade of aistopod tetrapodomorphss including the families Phlegethontiidae and Pseudophlegethontiidae. It is a stem-based taxon defined in phylogenetic terms as all aistopods sharing a more recent common ancestor with Phlegethontia than Oestocephalus.
Andersonerpeton is an extinct genus of aïstopod from the Bashkirian of Nova Scotia, Canada. It is known from a single jaw, which shares an unusual combination of features from both other aistopods and from stem-tetrapod tetrapodomorph fish. As a result, Andersonerpeton is significant for supporting a new classification scheme which states that aistopods evolved much earlier than previously expected. The genus contains a single species, A. longidentatum, which was previously believed to have been a species of the microsaur Hylerpeton.
