Lethiscus is the earliest known representative of the Aistopoda, a group of very specialised snake-like tetrapodomorphs known from the early Carboniferous (Mississippian).
Tetrapodomorpha is a clade of vertebrates consisting of tetrapods and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced forms transitional between fish and the early labyrinthodonts, such as Tiktaalik, have been referred to as "fishapods" by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains the crown group tetrapods and several groups of early stem tetrapods, which includes several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodomorpha minus the crown group Tetrapoda are the stem Tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition.
Phlegethontia is an extinct genus of aïstopod tetrapodomorphs from the Carboniferous and Permian periods of Europe and North America.
Tristichopterids (Tristichopteridae) were a diverse and successful group of fish-like tetrapodomorphs living throughout the Middle and Late Devonian. They first appeared in the Eifelian stage of the Middle Devonian. Within the group sizes ranged from a few tens of centimeters (Tristichopterus) to several meters.
Rhizodontida is an extinct group of predatory tetrapodomorphs known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 million years ago (Mya), the latest around 310 Mya. Rhizodonts lived in tropical rivers and freshwater lakes and were the dominant predators of their age. They reached huge sizes - the largest known species, Rhizodus hibberti from Europe and North America, was an estimated 7 m in length, making it the largest freshwater fish known.
Rhizodus is an extinct genus of basal, finned tetrapodomorphs. It belonged to Rhizodontida, one of the earliest-diverging tetrapodomorph clades. Two valid species have been described, both of which lived during the Early Carboniferous epoch. The type species R. hibberti is known from the Viséan stage of the United Kingdom, whereas the species R. serpukhovensis is from the Serpukhovian of Russia. Some fossils referred to the genus Rhizodus have also been found in North America.
Adelospondylus is an extinct adelospondyl tetrapodomorph from the Carboniferous of what is now Scotland.
Megalichthyidae is an extinct family of tetrapodomorphs which lived from the Middle–Late Devonian to the Early Permian. They are known primarily from freshwater deposits, mostly in the Northern Hemisphere, but one genus (Cladarosymblema) is known from Australia, and the possible megalichthyid Mahalalepis is from Antarctica.
Osteolepididae is a family of primitive, fish-like tetrapodomorphs that lived during the Devonian period. The family is generally thought to be paraphyletic, with the traits that characterise the family being widely distributed among basal tetrapodomorphs and other osteichthyans. Some of the genera historically placed in Osteolepididae have more recently been assigned to the family Megalichthyidae, which appears to be a monophyletic group.
Mahalalepis is an extinct genus of megalichthyid tetrapodomorphs which lived during the Devonian period.
Coloraderpeton is an extinct tetrapodomorph in the genus aïstopod 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.
Dolichopareias is an extinct genus of adelospondyl tetrapodomorph.
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.
Montcellia is an extinct genus of nectridean tetrapodomorphs within the family Urocordylidae that lived in the late Carboniferous period in the modern France.
Palaeomolgophis is an extinct genus of eel-like adelospondyl tetrapodomorphs containing a single species—Palaeomolgophis scoticus. Their limbs are much reduced, and they were probably fully aquatic.
Cryptolepis is an extinct genus of prehistoric marine lobe-finned fish known from the Late Devonian of what is now eastern Europe. It contains a single species, C. grossi from the middle to late Famennian of Oryol, Russia and Latvia. Scales of this species are particularly common in Devonian localities of Latvia. It was named after paleontologist Walter R. Gross.
Oestocephalidae is an extinct family of Late Carboniferous aistopod tetrapodomorphs. Fossils have been found from Ohio, Illinois, and Colorado in the United States; England; and the Czech Republic. It includes the genera Coloraderpeton and Oestocephalus. Oestocephalids have robust skulls and narrow, rounded snouts. They possess heavily ossified gastralia and dorsal osteoderms. Like other aïstopods, oestocephalids were elongate, having approximately 110 vertebrae. Oestocephalidae was named in 2003, with the type species being Oestocephalus amphiuminus.
Kyrinion is an extinct genus of baphetid tetrapodomorph from the Late Carboniferous of England. It is known from a skull that was found in Tyne and Wear county dating back to the Westphalian stage. Along with the skull is part of the lower jaw, an arch of the atlas bone and a rib possibly belonging to a cervical (neck) vertebra. The type species K. martilli was named from this material in 2003.
Eotetrapodiformes is a clade of tetrapodomorphs including the four-limbed vertebrates and their closest finned relatives, two groups of stem tetrapods called tristichopterids and elpistostegalids.
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.
Clement AM, Cloutier R, Lu J, Perilli E, Maksimenko A, Long J. 2021. A fresh look at Cladarosymblema narrienense, a tetrapodomorph fish (Sarcopterygii: Megalichthyidae) from the Carboniferous of Australia, illuminated via X-ray tomography. PeerJ 9:e12597 https://doi.org/10.7717/peerj.12597
