Lissamphibia
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The Lissamphibia is a group of
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s that includes all modern
amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s. Lissamphibians consist of three living groups: the
Salientia The Salientia (Latin ''salire'' (''salio''), "to jump") are a total group of amphibians that includes the order Anura, the frogs and toads, and various extinct proto-frogs that are more closely related to the frogs than they are to the Urodela ...
(
frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...
s,
toad Toad is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands. A distinction between frogs and toads is not made in scientif ...
s, and their extinct relatives), the
Caudata The Caudata are a group of amphibians containing the extant salamanders (Urodela) and all extinct species of amphibians more closely related to salamanders than to frogs. They are typically characterized by a superficially lizard-like appearance ...
(
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
s,
newt A newt is a salamander in the subfamily Pleurodelinae. The terrestrial juvenile phase is called an eft. Unlike other members of the family Salamandridae, newts are semiaquatic, alternating between aquatic and terrestrial habitats. Not all aqua ...
s, and their extinct relatives), and the
Gymnophiona Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics o ...
(the limbless
caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics of ...
s and their extinct relatives). A fourth group, the
Allocaudata The Albanerpetontidae are an extinct family of small amphibians, native to the Northern Hemisphere during the Mesozoic and Cenozoic. The only members of the order Allocaudata, they are thought to be allied with living amphibians belonging to Lissa ...
, was moderately successful, spanning 160 million years from the
Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
to the
Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
, but became extinct two million years ago. For several decades, this name has been used for a group that includes all living amphibians, but excludes all the main groups of Paleozoic tetrapods, such as
Temnospondyli Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...
,
Lepospondyli Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco ('' Diplocaulus minumus''), lepospondyls lived from the Early Carboniferous ( Mississippian) to the Early Pe ...
,
Embolomeri Embolomeri is an order of tetrapods or stem-tetrapods, possibly members of Reptiliomorpha. Embolomeres first evolved in the Early Carboniferous ( Mississippian) Period and were the largest and most successful predatory tetrapods of the Late Carb ...
, and
Seymouriamorpha Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are ...
. Some scientists have concluded that all of the primary groups of modern amphibians—
frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...
s,
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
s and
caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics of ...
s—are closely related. Some writers have argued that the early
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
dissorophoid Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
''
Gerobatrachus hottoni ''Gerobatrachus'' is an extinct genus of amphibamid temnospondyl (represented by the type species ''Gerobatrachus hottoni'') that lived in the Early Permian, approximately 290 million years ago (Ma), in the area that is now Baylor County, Texas ...
'' is a lissamphibian. If it is not, the earliest known lissamphibians are ''
Triadobatrachus ''Triadobatrachus'' is an extinct genus of salientian frog-like amphibians, including only one known species, ''Triadobatrachus massinoti''. It is the oldest member of the frog lineage known, and an excellent example of a transitional fossil. It ...
'' and ''
Czatkobatrachus ''Czatkobatrachus'' is an extinct genus of Early Triassic (Olenekian) salientian amphibians. It was first described in 1998 based on fossils found in the 1 quarry in Poland. It is, with ''Triadobatrachus'', one of the two oldest known lissamphi ...
'' from the
Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...
.


Characteristics

Some, if not all, lissamphibians share the following characteristics. Some of these apply to the soft body parts, hence do not appear in fossils. However, the skeletal characteristics also appear in several types of Palaeozoic amphibians: * Double or paired
occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...
s * Two types of skin glands (mucous and granular) *
Fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...
bodies associated with
gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
s * Double-channeled sensory papillae in the inner
ear An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of ...
*
Green rod Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a combin ...
s (a special type of visual cell, unknown in caecilians) * Ribs do not encircle body. Anurans do not have ribs. * Ability to elevate the eyes (with the levator bulbi muscle) * Forced-pump respiratory mechanism, the primitive breathing system also found in labyrinthodont amphibians * Cylindrical centra (the main body of the
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e; cylindrical centra are also found in several groups of early
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s) *
Pedicellate teeth Pedicellate teeth are a tooth morphology today unique to modern amphibians, but also seen in a variety of extinct labyrinthodonts. Pedicellate teeth consist of a tooth crown and a base (both composed of dentine) separated by a layer of uncalcifie ...
(the crowns of the teeth are separated from the roots by a zone of fibrous tissue; also found in some
Dissorophoidea Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
; the teeth of some fossil
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
s are not pedicellate) * Bicuspid teeth (two cusps per tooth, also found in juvenile
dissorophoids Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
) * Operculum (small bone in the skull, linked to shoulder girdle by the opercularis muscle; perhaps involved in hearing and balance; absent in caecilians and some salamanders, fused to the columella (ear bone) in most anurans) * Loss of posterior
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
bones (also in
Microsauria Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considere ...
and
Dissorophoidea Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
) * Small, widely separated
pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates, behind the palatine bone In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the th ...
s (also found in
Temnospondyli Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...
and
Nectridea 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 the ...
) * Wide cultriform process of the parasphenoid (also found in some
Microsauria Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considere ...
(''Rhynchonkos'') and
Lysorophia 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 (previously known as Lysoro ...
)


Relationships and definition

The features uniting the Lissamphibia were first noted by
Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; 16 February 1834 – 9 August 1919) was a German zoologist, naturalist, eugenicist, philosopher, physician, professor, marine biologist and artist. He discovered, described and named thousands of new sp ...
, even though in Haeckel's work, Lissamphibia excluded the
caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics of ...
s. Nevertheless, Haeckel considered the caecilians to be closely related to what he called Lissamphibia (gr. λισσός, smooth), which is now called Batrachia and includes
frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...
s and
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
s. In the early to mid 20th century, a biphyletic origin of amphibians (and thus of
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s in general) was favoured. In the late 20th century, a flood of new fossil evidence mapped out in some detail the nature of the transition between the elpistostegalid fish and the early amphibians. Most
herpetologists Herpetology (from Greek ἑρπετόν ''herpetón'', meaning " reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnophiona)) and r ...
and
paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
s, therefore, no longer accept the view that amphibians have arisen twice, from two related but separate groups of fish. The question then arises whether Lissamphibia is
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
as well. Unfortunately, the origin and relationships of the various lissamphibian groups both with each other and among other early
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s remain controversial. Not all paleontologists today are convinced that Lissamphibia is indeed a natural group, as there are important characteristics shared with some non-lissamphibian Palaeozoic amphibians. Currently, the two prevailing theories of lissamphibian origin are: * Monophyletic within
Temnospondyli Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...
* Monophyletic within
Lepospondyli Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco ('' Diplocaulus minumus''), lepospondyls lived from the Early Carboniferous ( Mississippian) to the Early Pe ...
One of the hypotheses regarding their ancestors is that they evolved by paedomorphosis and miniaturization from early tetrapods. Recent molecular studies of extant amphibians based on multiple-locus data favor one or the other of the monophyletic alternatives and indicate a
Late Carboniferous Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
date for the divergence of the lineage leading to caecilians from the one leading to frogs and salamanders, and an early Permian date for the separation of the frog and salamander groups.


References


Bibliography

* Benton, M. J. (2005), ''
Vertebrate Palaeontology Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossilized remains, the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord. It also tries to connect, by u ...
'', 3rd ed. Blackwell. * Carroll, R. L. (1988), ''
Vertebrate Paleontology and Evolution ''Vertebrate Paleontology and Evolution'' is an advanced textbook on vertebrate paleontology by Robert L. Carroll, published in 1988 by WH Freeman. It provides a very detailed technical account of various groups of living and fossil vertebrate ...
'', WH Freeman & Co. *


External links


Biology 356 - Major Features of Vertebrate Evolution
by Dr. Robert Reisz, University of Toronto {{portalbar, Amphibians Amphibians Extant Early Triassic first appearances Taxa named by Ernst Haeckel