Reptiliomorpha
Encyclopedia
Reptiliomorpha refers to an order or subclass of reptile-like amphibians, which gave rise to the amniote
s in the Carboniferous
. Under phylogenetic nomenclature
, the Reptiliomorpha includes their amniote descendants though, even in phylogenetic nomenclature, the name is mostly used when referring to the non-amniote reptile
-like labyrinthodont
grade. An alternative name, Anthracosauria is commonly used for the group, but is confusingly also used for the "lower" grade
of reptiliomorphs by Benton
.
labyrinthodonts and the first reptiles
. University of Bristol paleontologist Professor Michael J. Benton
gives the following characteristics for the Reptiliomorpha:
and cheek. The deeper skull allowed for laterally placed eyers, contrary to dorsally placed eyers commonly found in amphibians. The skulls of the group are usually found with fine radiating grooves. The back of the skull held a deep otic notch in quadrate bone
, likely holding a spiracle
rather than a tympanum
.
descendants. They did however lack the reptilian type of ankle bone that would have allowed the use of the feet as levers for propulsion rather than as holdfasts.
ns and some seymouriamorpha
ns, like Discosauriscus
, dermal scales are found in post-metamorphic specimens, indicating they may have had a "knobbly" if not scaly appearance.
They reproduced in amphibian fashion with aquatic egg
s that hatched into larva
e (tadpoles) with external gills.
During the Carboniferous
and Permian
periods, tetrapod
s evolved along a number of parallel lines towards a reptilian
condition. Some of these tetrapods (e.g. Archeria, Eogyrinus
) were elongate, eel-like aquatic forms with diminutive limbs, while others (e.g. Seymouria
, Solenodonsaurus
, Diadectes
, Limnoscelis
) were so reptile-like that until quite recently they actually had been considered true reptiles, and it is likely that to a modern observer they would have appeared as large to medium-sized, heavy-set lizard
s. Several groups however remained aquatic or semiaquatic. The chroniosuchia
ns show the build and presumably habit similar to modern crocodiles as river-side predators, while the Chroniosuchia
was either crocodile like or with elongated newt
- or eel
-like proportions. The two most terrestrially adapted groups were the medium sized insectivorous or carnivorous Seymouriamorpha
and the mainly herbivorous Diadectomorpha
, with many large forms. The latter group is in most analysis the closest relatives of the Amniote
s.
With their terrestrial life style combined with the need to return to the water to lay egg
s hatching to larva
e (tadpoles) lead to a drive to abandon the larval stage and aquatic eggs. A possible reason may have been competition for breeding ponds, to exploit drier environments with less access to open water, or to avoid predation on tadpoles by fish, a problem still plaguing modern amphibians. Whatever the reason, the drive led to internal fertilization
and direct development (completing the tadpole stage within the egg). A striking parallel can be seen in the frog family Leptodactylidae
, which has a very diverse reproductive system, including foam nests, non-feeding terrestrial tadpoles and direct development. The Diadectomorphans generally being large animals would have had correspondingly large eggs, unable to survive on land.
Fully terrestrial life was achieved with the development of the amniote egg, where a number of membranous sacks protect the embryo
and facilitating gas exchange between the egg and the atmosphere. The first to evolve was probably the allantois
, a sack that develops from the gut/yolk-sack. This sack contains the embryo's nitrogenous waste (urea
) during development, stopping it from poisoning the embryo. A very small allantois is found in modern amphibians. Later came the amnion
surrounding the fetus proper, and the chorion
, encompassing the amnion, allantois, and yolk-sack.
Exactly where the border between reptile-like amphibians (non-amniote reptiliomorphs) and amniotes lies will probably never be known, as the reproductive structures involved fossil
ize poorly, but various small, advanced reptiliomorphs have been suggested as the first true amniotes, including Gephyrostegus, Casineria
and Westlothiana
. Such small animals lay small eggs, 1 cm in diameter or less. Such eggs will have a small enough volume to surface ratio to be able to develop on land without the amnion and chorin actively effecting gas exchange, setting the stage for the evolution of true amniotic eggs. Although the first amniote probably appeared as early as the latest Mississippian period (Middle Carboniferous), non-amniote (or amphibian) reptiliomorphs continued to flourish alongside their amniote descendants for many millions of years. By the middle Permian the non-amniote terrestrial
forms had died out, but several aquatic
non-amniote groups continued to the end of the Permain, and in the case of the Chroniosuchids
survived the end Permian mass extinction, only to die out at the end of the Early Triassic
. Meanwhile, the single most successful daughter-clade of the reptiliomorphs, the amniotes, continued to flourish and to inherit the Earth
.
in 1934 to designate various types of late Paleozoic reptile-like labyrinthodont "amphibian
s." However Alfred Sherwood Romer
used the name Anthracosauria
instead. In 1970, the German paleontologist Panchen reverted to Säve-Söderberghs definition, but Romer's terminology is still in use, e.g. Carroll 1988 and 2002, and Hildebrand & Goslow 2001. Some cladistic
also work prefer Anthracosauria.
In 1956 Friedrich von Huene
included both amphibians and anapsid reptile
s in the Reptiliomorpha. This included the following orders: 1. Anthracosauria
, 2. Seymouriamorpha
, 3. Microsauria
, 4. Diadectomorpha
, 5. Procolophonia
, 6. Pareiasaur
ia, 7. Captorhinidia
, 8. Testudinata.
In 1997 Michel Laurin
and Robert Reisz (1997) adapted the term in a cladistic sense. Michael Benton
(2000, 2004) made it the sister-clade to Batrachomorpha
. However, when considered a linnean ranking, Reptiliomorpha is given the rank of superorder and only includes reptile-like amphibians, not their amniote descendants. More recently Reptiliomorpha has been adopted as the term for the largest clade that includes – according to the technical definitions of the phylocode
which only refers to species
or genus
level organisms – Homo sapiens but not Ascaphus truei (a primitive frog
) (International Phylogenetic Nomenclature Meeting 2003); or is, as Toby White (Palaeos
website) puts it, more like dogs than frogs (i.e. mammal
s but not amphibian
s). However, given the lack of consensus of the phylogeny of the labyrinthodonts in general, and the origin of modern amphibians
in particular, the actual content of the Reptiliomorpha under the latter definition is uncertain.
Amniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
s in the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
. Under phylogenetic nomenclature
Phylogenetic nomenclature
Phylogenetic nomenclature or phylogenetic taxonomy is an alternative to rank-based nomenclature, applying definitions from cladistics . Its two defining features are the use of phylogenetic definitions of biological taxon names, and the lack of obligatory ranks...
, the Reptiliomorpha includes their amniote descendants though, even in phylogenetic nomenclature, the name is mostly used when referring to the non-amniote reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
-like labyrinthodont
Labyrinthodontia
Labyrinthodontia is an older term for any member of the extinct subclass of amphibians, which constituted some of the dominant animals of Late Paleozoic and Early Mesozoic times . The group is ancestral to all extant landliving vertebrates, and as such constitutes an evolutionary grade rather...
grade. An alternative name, Anthracosauria is commonly used for the group, but is confusingly also used for the "lower" grade
Evolutionary grade
In alpha taxonomy, a grade refers to a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.-Definition:...
of reptiliomorphs by Benton
Michael Benton
Michael J. Benton is a British paleontologist, a Fellow of the Royal Society of Edinburgh, and professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol....
.
Characteristics
Basal reptiliomorphs were land-based, reptile-like amphibians, in anatomy falling between the mainly aquatic DevonianDevonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
labyrinthodonts and the first reptiles
Captorhinidae
Captorhinidae is one of the earliest and most basal reptile families.-Description:...
. University of Bristol paleontologist Professor Michael J. Benton
Michael J. Benton
Michael J. Benton is a British paleontologist, a Fellow of the Royal Society of Edinburgh, and professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol....
gives the following characteristics for the Reptiliomorpha:
- narrow premaxillaPremaxillaThe incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
e (less than half the skull width) - vomers taper forward
- phalangeal formulae (number of joints in each toe) of foot 2.3.4.5.4–5
Cranium morphology
The group differ from the contemporary non-reptiliomorph labyrinthodonts by having a deeper and taller skull, but retained the primitive kinesis (loose attachment) between skull roofSkull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...
and cheek. The deeper skull allowed for laterally placed eyers, contrary to dorsally placed eyers commonly found in amphibians. The skulls of the group are usually found with fine radiating grooves. The back of the skull held a deep otic notch in quadrate bone
Quadrate bone
The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids , and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint .- Evolutionary variation :In snakes, the quadrate bone has become elongated...
, likely holding a spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
rather than a tympanum
Tympanum (zoology)
The tympanum is an external hearing structure in animals such as frogs, toads, insects, and mammals, to name a few.-Anurans:In frogs and toads, it is located just behind the eye. It does not actually process sound waves; it simply transmits them to the amphibian's inner ear, which is protected...
.
Postcranial skeleton
The vertebrae showed the typical multi-element construction as seen in labyrinthodonts, but with pleurocentrum being the dominant element. Unlike most labyrinthonts, the body was moderatly deep rather than flat, and the limbs was well-developed and ossified, indicating a predominately terrestrial lifestyle except in secondarily aquatic groups. Each foot held 5 digits, the pattern seen in their amnioteAmniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
descendants. They did however lack the reptilian type of ankle bone that would have allowed the use of the feet as levers for propulsion rather than as holdfasts.
Physiology
The general build was heavy in all forms, though otherwise very similar to that of early reptiles. The skin, at least in the more advanced forms probably had a water-tight epidermal horny overlay, like seen in today's reptiles, though they lacked horny claws. In chroniosuchiaChroniosuchia
The Chroniosuchia are a suborder or order of labyrinthodonts that lived in the middle Permian and the upper Triassic periods of Eastern Europe, Kyrgyzstan, China and Germany. They were all rather short limbed with a strong tail and elongated snout, somewhat resembling modern crocodiles...
ns and some seymouriamorpha
Seymouriamorpha
Seymouriamorpha were a small but widespread group of reptiliomorphs. Many seymouriamorphs were terrestrial or semi-aquatic. However, aquatic larvae bearing external gills and grooves from the lateral line system has been found, making them unquestionably amphibians. The adults were terrestrial...
ns, like Discosauriscus
Discosauriscus
Discosauriscus was a small reptiliomorph that lived in Central and Western Europe in the Lower Permian Period. Its best fossils have been found in Boskovice Furrow, in the Czech Republic.-Classification:thumb|180px|left|Discosauriscus...
, dermal scales are found in post-metamorphic specimens, indicating they may have had a "knobbly" if not scaly appearance.
They reproduced in amphibian fashion with aquatic egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s that hatched into larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e (tadpoles) with external gills.
Evolutionary history
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
periods, tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s evolved along a number of parallel lines towards a reptilian
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
condition. Some of these tetrapods (e.g. Archeria, Eogyrinus
Eogyrinus
Eogyrinus was one of the largest Carboniferous tetrapods, and perhaps one of the largest of its family, Eogyrinidae, at in length....
) were elongate, eel-like aquatic forms with diminutive limbs, while others (e.g. Seymouria
Seymouria
Seymouria was a reptile-like labyrinthodont from the early Permian of North America and Europe . It was small, only 2 ft long...
, Solenodonsaurus
Solenodonsaurus
Solenodonsaurus is an extinct genus of Reptiliomorpha, which lived about 320-305 million years ago. Classification is uncertain, but it was possibly an early reptile or an amphibian close to the diadectomorphs. Its remains were found in the Czech Republic...
, Diadectes
Diadectes
Diadectes was a genus of large, very reptile-like amphibians that lived during the early Permian period...
, Limnoscelis
Limnoscelis
Limnoscelis is a genus of large, very reptile-like diadectomorph from the Early Permian of North America. Contrary to other diadectomorphans, Limnoscelis appear to have been a carnivore...
) were so reptile-like that until quite recently they actually had been considered true reptiles, and it is likely that to a modern observer they would have appeared as large to medium-sized, heavy-set lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s. Several groups however remained aquatic or semiaquatic. The chroniosuchia
Chroniosuchia
The Chroniosuchia are a suborder or order of labyrinthodonts that lived in the middle Permian and the upper Triassic periods of Eastern Europe, Kyrgyzstan, China and Germany. They were all rather short limbed with a strong tail and elongated snout, somewhat resembling modern crocodiles...
ns show the build and presumably habit similar to modern crocodiles as river-side predators, while the Chroniosuchia
Chroniosuchia
The Chroniosuchia are a suborder or order of labyrinthodonts that lived in the middle Permian and the upper Triassic periods of Eastern Europe, Kyrgyzstan, China and Germany. They were all rather short limbed with a strong tail and elongated snout, somewhat resembling modern crocodiles...
was either crocodile like or with elongated newt
Newt
A newt is an aquatic amphibian of the family Salamandridae, although not all aquatic salamanders are considered newts. Newts are classified in the subfamily Pleurodelinae of the family Salamandridae, and are found in North America, Europe and Asia...
- or eel
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
-like proportions. The two most terrestrially adapted groups were the medium sized insectivorous or carnivorous Seymouriamorpha
Seymouriamorpha
Seymouriamorpha were a small but widespread group of reptiliomorphs. Many seymouriamorphs were terrestrial or semi-aquatic. However, aquatic larvae bearing external gills and grooves from the lateral line system has been found, making them unquestionably amphibians. The adults were terrestrial...
and the mainly herbivorous Diadectomorpha
Diadectomorpha
Diadectomorpha are a clade of large reptile-like amphibians that lived in Euramerica during the Carboniferous and Early Permian periods, and are very close to the ancestry of the Amniota. They include both large carnivorous and even larger herbivorous forms, some semi-aquatic and others fully...
, with many large forms. The latter group is in most analysis the closest relatives of the Amniote
Amniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
s.
With their terrestrial life style combined with the need to return to the water to lay egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s hatching to larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e (tadpoles) lead to a drive to abandon the larval stage and aquatic eggs. A possible reason may have been competition for breeding ponds, to exploit drier environments with less access to open water, or to avoid predation on tadpoles by fish, a problem still plaguing modern amphibians. Whatever the reason, the drive led to internal fertilization
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...
and direct development (completing the tadpole stage within the egg). A striking parallel can be seen in the frog family Leptodactylidae
Leptodactylidae
Leptodactylidae is a diverse family of frogs that probably diverged from other hyloids during the Cenozoic era, or possibly at the end of the Mesozoic. There are roughly 50 genera, one of which is Eleutherodactylus, the largest vertebrate genus, with over 700 species...
, which has a very diverse reproductive system, including foam nests, non-feeding terrestrial tadpoles and direct development. The Diadectomorphans generally being large animals would have had correspondingly large eggs, unable to survive on land.
Fully terrestrial life was achieved with the development of the amniote egg, where a number of membranous sacks protect the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
and facilitating gas exchange between the egg and the atmosphere. The first to evolve was probably the allantois
Allantois
Allantois is a part of a developing animal conceptus . It helps the embryo exchange gases and handle liquid waste....
, a sack that develops from the gut/yolk-sack. This sack contains the embryo's nitrogenous waste (urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
) during development, stopping it from poisoning the embryo. A very small allantois is found in modern amphibians. Later came the amnion
Amnion
The amnion is a membrane building the amniotic sac that surrounds and protects an embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota”; but not in amphibians and fish , which are consequently termed “Anamniota”. The primary role of this is the protection of the...
surrounding the fetus proper, and the chorion
Chorion
The chorion is one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes...
, encompassing the amnion, allantois, and yolk-sack.
Exactly where the border between reptile-like amphibians (non-amniote reptiliomorphs) and amniotes lies will probably never be known, as the reproductive structures involved fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ize poorly, but various small, advanced reptiliomorphs have been suggested as the first true amniotes, including Gephyrostegus, Casineria
Casineria
Casineria was a tetrapod which lived 340 million years ago in the Mississippian epoch. Casineria was a small animal with a total length estimated to have been 15 centimeters. It lived in what was then a fairly dry environment in Scotland. It is noted for its mix of primitive and advanced ...
and Westlothiana
Westlothiana
Westlothiana lizziae was a reptile-like amphibian or possibly early reptile that bore a superficial resemblance to modern-day lizards. It lived during the Carboniferous period, about 350 million years ago. The type specimen was discovered in East Kirkton Quarry, Bathgate, Scotland, in 1984, and was...
. Such small animals lay small eggs, 1 cm in diameter or less. Such eggs will have a small enough volume to surface ratio to be able to develop on land without the amnion and chorin actively effecting gas exchange, setting the stage for the evolution of true amniotic eggs. Although the first amniote probably appeared as early as the latest Mississippian period (Middle Carboniferous), non-amniote (or amphibian) reptiliomorphs continued to flourish alongside their amniote descendants for many millions of years. By the middle Permian the non-amniote terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
forms had died out, but several aquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...
non-amniote groups continued to the end of the Permain, and in the case of the Chroniosuchids
Chroniosuchidae
The Chroniosuchidae are a family of semi-aquatic reptiliomorp amphibians found in sediments from the upper Permian and the upper Triassic periods, most in Russia. They were generally rather large animals, with long jaws similar to those found in modern crocodiles, and probably lived a similar life...
survived the end Permian mass extinction, only to die out at the end of the Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
. Meanwhile, the single most successful daughter-clade of the reptiliomorphs, the amniotes, continued to flourish and to inherit the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
.
Changing Definitions
The name Reptiliomorpha was coined by Professor Gunnar Säve-SöderberghGunnar Säve-Söderbergh
Gunnar Säve-Söderbergh was a Swedish palaeontologist and geologist. Säve-Söderbergh was born at Falun, the son of the neurologist Gotthard Söderbergh and Inga Säve. He passed his G.C.E. at Gothenburg in 1928 and took bachelor's and licentiate's degrees at Uppsala University in 1931 and 1933,...
in 1934 to designate various types of late Paleozoic reptile-like labyrinthodont "amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s." However Alfred Sherwood Romer
Alfred Romer
Alfred Sherwood Romer was an American paleontologist and comparative anatomist and a specialist in vertebrate evolution.-Biography:...
used the name Anthracosauria
Anthracosauria
Anthracosauria is an order of extinct reptile-like amphibians that flourished during the Carboniferous and early Permian periods, although precisely which species are included depends on one's definition of the taxon.-Various definitions:...
instead. In 1970, the German paleontologist Panchen reverted to Säve-Söderberghs definition, but Romer's terminology is still in use, e.g. Carroll 1988 and 2002, and Hildebrand & Goslow 2001. Some cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
also work prefer Anthracosauria.
In 1956 Friedrich von Huene
Friedrich von Huene
Friedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
included both amphibians and anapsid reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s in the Reptiliomorpha. This included the following orders: 1. Anthracosauria
Anthracosauria
Anthracosauria is an order of extinct reptile-like amphibians that flourished during the Carboniferous and early Permian periods, although precisely which species are included depends on one's definition of the taxon.-Various definitions:...
, 2. Seymouriamorpha
Seymouriamorpha
Seymouriamorpha were a small but widespread group of reptiliomorphs. Many seymouriamorphs were terrestrial or semi-aquatic. However, aquatic larvae bearing external gills and grooves from the lateral line system has been found, making them unquestionably amphibians. The adults were terrestrial...
, 3. Microsauria
Microsauria
Microsauria is an extinct order of lepospondyl amphibians from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considered paraphyletic, as several other non-microsaur lepospondyl groups such as...
, 4. Diadectomorpha
Diadectomorpha
Diadectomorpha are a clade of large reptile-like amphibians that lived in Euramerica during the Carboniferous and Early Permian periods, and are very close to the ancestry of the Amniota. They include both large carnivorous and even larger herbivorous forms, some semi-aquatic and others fully...
, 5. Procolophonia
Procolophonia
The Procolophonia are a suborder of herbivorous reptiles that lived from the Middle Permian till the end of the Triassic period. They were originally included as a suborder of the Cotylosauria but are now considered a clade of Parareptilia...
, 6. Pareiasaur
Pareiasaur
The Pareiasaurs - Family Pareiasauridae - are a clade of medium-sized to large herbivorous anapsid reptiles that flourished during the Permian period....
ia, 7. Captorhinidia
Captorhinomorpha
Captorhinomorpha is a suborder of prehistoric reptiles which appeared in the Carboniferous period and became extinct after the Early Permian period....
, 8. Testudinata.
In 1997 Michel Laurin
Michel Laurin
Michel Laurin is a Canadian vertebrate paleontologist specialising in the origin and phylogeny of tetrapods, comparative biology and paleobiology. As an undergraduate he worked in the laboratory of Robert L. Carroll, and took his doctor thesis on the osteology of seymouriamorphs under Robert R....
and Robert Reisz (1997) adapted the term in a cladistic sense. Michael Benton
Michael J. Benton
Michael J. Benton is a British paleontologist, a Fellow of the Royal Society of Edinburgh, and professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol....
(2000, 2004) made it the sister-clade to Batrachomorpha
Batrachomorpha
Batrachomorpha is a name traditionally given to recent and extinct amphibians that are not related to reptiles. It most often includes the extinct groups Temnospondyli and Lepospondyli.-Origin of the term:...
. However, when considered a linnean ranking, Reptiliomorpha is given the rank of superorder and only includes reptile-like amphibians, not their amniote descendants. More recently Reptiliomorpha has been adopted as the term for the largest clade that includes – according to the technical definitions of the phylocode
PhyloCode
The International Code of Phylogenetic Nomenclature, known as the PhyloCode for short, is a developing draft for a formal set of rules governing phylogenetic nomenclature...
which only refers to species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
or genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
level organisms – Homo sapiens but not Ascaphus truei (a primitive frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
) (International Phylogenetic Nomenclature Meeting 2003); or is, as Toby White (Palaeos
Palaeos
Palaeos.com is a web site on biology, paleontology, cladistics and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of vertebrate palaeontology in the Department of...
website) puts it, more like dogs than frogs (i.e. mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s but not amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s). However, given the lack of consensus of the phylogeny of the labyrinthodonts in general, and the origin of modern amphibians
Lissamphibia
The subclass Lissamphibia includes all recent amphibians and means smooth amphibia.Extant amphibians fall into one of three orders — the Anura , the Caudata or Urodela , and the Gymnophiona or Apoda .Although the ancestry of each group is still unclear, all share certain common characteristics,...
in particular, the actual content of the Reptiliomorpha under the latter definition is uncertain.
Taxonomy
Classification after Benton (1997):- Superclass Tetrapoda
- Superorder Reptiliomorpha
- Family CaerorhachidaeCaerorhachisCaerorhachis is an extinct genus of early tetrapod from the Early Carboniferous of Scotland. Its placement within Tetrapoda is uncertain, but it is generally regarded as a primitive member of the group. The type species C...
- Family Tokosauridae
- Order ChroniosuchiaChroniosuchiaThe Chroniosuchia are a suborder or order of labyrinthodonts that lived in the middle Permian and the upper Triassic periods of Eastern Europe, Kyrgyzstan, China and Germany. They were all rather short limbed with a strong tail and elongated snout, somewhat resembling modern crocodiles...
- Family Bystrowianidae
- Family ChroniosuchidaeChroniosuchidaeThe Chroniosuchidae are a family of semi-aquatic reptiliomorp amphibians found in sediments from the upper Permian and the upper Triassic periods, most in Russia. They were generally rather large animals, with long jaws similar to those found in modern crocodiles, and probably lived a similar life...
- Order EmbolomeriEmbolomeriThe Embolomeri is a suborder of Reptiliomorpha. The Embolomeri first evolved from reptile-like amphibians in the Early Carboniferous...
- Family EoherpetontidaeEoherpetontidaeEoherpeton is the only genus of the family Eoherpetontidae in the extinct suborder Embolomeri....
- Family AnthracosauridaeAnthracosaurusAnthracosaurus is an extinct genus of labyrinthodont that lived in the Carboniferous period. Anthracosaurus belongs to the suborder of Embolomeri....
- Family ProterogyrinidaeProterogyrinidaeThe Proterogyrinidae was a family of Embolomeri that lived in the Carboniferous period. Typical genus was Proterogyrinus....
- Family EogyrinidaeEogyrinidaeEogyrinidae is an extinct family of large, long-bodied tetrapods that lived in the rivers of the Late Carboniferous period....
- Family ArcheriidaeArcheriidaeArcheriidae is a family of embolomeres that lived in the Permian period. Archeria is a well known genus of archeriid....
- Family Eoherpetontidae
- Order SeymouriamorphaSeymouriamorphaSeymouriamorpha were a small but widespread group of reptiliomorphs. Many seymouriamorphs were terrestrial or semi-aquatic. However, aquatic larvae bearing external gills and grooves from the lateral line system has been found, making them unquestionably amphibians. The adults were terrestrial...
- Family Kotlassiidae
- Family DiscosauriscidaeDiscosauriscidaeDiscosauriscidae is a family of reptiliomorphs of the early Permian group Seymouriamorpha....
- Family Seymouriidae
- Order DiadectomorphaDiadectomorphaDiadectomorpha are a clade of large reptile-like amphibians that lived in Euramerica during the Carboniferous and Early Permian periods, and are very close to the ancestry of the Amniota. They include both large carnivorous and even larger herbivorous forms, some semi-aquatic and others fully...
- Family LimnoscelidaeLimnoscelidaeLimnoscelidae is a family of carnivorous Diadectomorphans. They would have been the largest terrestrial carnivores of their day, the other large carnivores being aquatic or semi aquatic labyrinthodont amphibians...
- Family DiadectidaeDiadectidaeDiadectidae is an extinct family of large diadectomorph reptiliomorphs. Diadectids lived in North America and Europe during the Late Carboniferous and Early Permian. They were the first herbivorous tetrapods, and also the first fully terrestrial animals to attain large sizes. Footprints indicate...
- Family Limnoscelidae
- Series Amniota
- Family Caerorhachidae
- Superorder Reptiliomorpha