Lissamphibia
Encyclopedia
The subclass Lissamphibia includes all recent amphibian
s and means smooth amphibia.
Extant amphibians fall into one of three orders — the Anura (frog
s and toad
s), the Caudata or Urodela (salamander
s and newt
s), and the Gymnophiona or Apoda (the limbless caecilian
s).
Although the ancestry of each group is still unclear, all share certain common characteristics, which indicates they evolved from a common ancestor and so form a clade
. The publication of a Permian-period stem form Gerobatrachus hottoni showed the frogs and salamanders had a common ancestor more recently (ca 290 Ma) than had been thought by using the molecular clock
alone.
. In the early to mid 20th cetury, a bipyletic origin of amphibians (and thus of tetrapod
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 paleontologists no longer accept the diphyletic view. Whilst the monophyly of the Lissamphibia is accepted by most herpetologists
and paleontologists, the origin and relationships of the various Lissamphibian groups both with each other and among other early tetrapod
s remains controversial. Not all paleontologists are convinced that the lissamphibia are indeed a natural group, as the various characteristics are also shared with some Palaeozoic amphibians, and it is still possible that these characteristics evolved independently.
Currently there are three prevailing theories of Lissamphibian origin:
Most molecular studies of extant amphibians support monophyly
for caecilians, frogs, and salamanders, and the most recent molecular study based on multi-locus data suggest a Late Carboniferous
- Early Permian
origin of modern amphibians.
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 and means smooth amphibia.
Extant amphibians fall into one of three orders — the Anura (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...
s and toad
Toad
A toad is any of a number of species of amphibians in the order Anura characterized by dry, leathery skin , short legs, and snoat-like parotoid glands...
s), the Caudata or Urodela (salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s and 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...
s), and the Gymnophiona or Apoda (the limbless caecilian
Caecilian
The caecilians are an order of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly...
s).
Although the ancestry of each group is still unclear, all share certain common characteristics, which indicates they evolved from a common ancestor and so form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
. The publication of a Permian-period stem form Gerobatrachus hottoni showed the frogs and salamanders had a common ancestor more recently (ca 290 Ma) than had been thought by using the molecular clock
Molecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
alone.
Characteristics
The following characteristics are shared by some, most, or all Lissamphibia. Some of these apply to the soft body parts and hence not present in fossils. However, those which refer to the skeleton are also known from several types of Palaeozoic amphibians:- Double or paired occipital condyleOccipital condyleThe occipital condyles are undersurface facets of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra....
- Two types of skin glandSkin glandSkin glands are structures found in mammals that play roles in thermoregulation and excretion....
s (mucous & granular) - FatFatFats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
bodies associated with gonadGonadThe gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s - Double-channeled sensory papillae in the inner earEarThe ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
- Green rods (a special type of visual cell, unknown in caecilians)
- RibRibIn vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
s do not encircle body - Ability to elevate the eyeEyeEyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
(with levetator bulbi muscle) - Forced pump respiratory mechanism
- Cylindrical centra (the main body of the vertebra; cylindrical centra are also found in several groups of early tetrapodTetrapodTetrapods 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) - Pedicellate teethPedicellate teethPedicellate 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 separated by a layer of uncalcified dentine....
(the crown of the teeth is separated from the root by a zone of fibrous tissue; also found in some DissorophoideaDissorophoideaDissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Late Pennsylvanian in Euramerica, and continued through to the Late Permian and even possibly the Early Triassic of Gondwana...
; the teeth of some fossil salamanderSalamanderSalamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s are not pedicellate) - Bicuspid teeth (two cuspCusp (dentistry)A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
s per tooth, also found in juvenile dissorophoidsDissorophoideaDissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Late Pennsylvanian in Euramerica, and continued through to the Late Permian and even possibly the Early Triassic of Gondwana...
) - OperculumOperculum (fish)The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
(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 stapes (ear bones) in most anurans) - Loss of posterior skullSkullThe skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
bones (also in MicrosauriaMicrosauriaMicrosauria 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...
and DissorophoideaDissorophoideaDissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Late Pennsylvanian in Euramerica, and continued through to the Late Permian and even possibly the Early Triassic of Gondwana...
) - Small, widely separated pterygoidPterygoidPterygoid can refer to:* Pterygoid processes of the sphenoid bone** The Lateral pterygoid plate by it* a muscle such as Lateral pterygoid muscle or Medial pterygoid muscle* a branch of the Mandibular nerve...
s (also found in TemnospondyliTemnospondyliTemnospondyli is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent...
and NectrideaNectrideaNectridea is an extinct order of lepospondyl amphibians from the Carboniferous and Permian periods, which included animals such as Diplocaulus. In appearance, they would have resembled modern newts or aquatic salamanders. They had long flattened tails to aid in swimming, and well-developed hind...
) - Wide cultriform process of the parasphenoid (also found in some MicrosauriaMicrosauriaMicrosauria 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...
(Rhynchonchos) and LysorophiaLysorophiaLysorophia is an order of aquatic Carboniferous and Permian amphibians within the extinct subclass Lepospondyli. Lysorophians resembled small snakes, as their bodies are extremely elongate. There is a single family, the Lysorophidae...
)
Relationships and definition
The features uniting the Lissamphibia were first noted by Ernst HaeckelErnst Haeckel
The "European War" became known as "The Great War", and it was not until 1920, in the book "The First World War 1914-1918" by Charles à Court Repington, that the term "First World War" was used as the official name for the conflict.-Research:...
. In the early to mid 20th cetury, a bipyletic origin of amphibians (and thus of 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 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
Elpistostegalia
Elpistostegalia or Panderichthyida is an order of prehistoric lobe-finned fishes which lived during the Late Devonian period . They represent the advanced tetrapodomorph stock, the fishes more closely related to tetrapods than the osteolepiform fishes...
and the early amphibians, most paleontologists no longer accept the diphyletic view. Whilst the monophyly of the Lissamphibia is accepted by most herpetologists
Herpetology
Herpetology is the branch of zoology concerned with the study of amphibians and reptiles...
and paleontologists, the origin and relationships of the various Lissamphibian groups both with each other and among other early 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 remains controversial. Not all paleontologists are convinced that the lissamphibia are indeed a natural group, as the various characteristics are also shared with some Palaeozoic amphibians, and it is still possible that these characteristics evolved independently.
Currently there are three prevailing theories of Lissamphibian origin:
- Monophyletic within the temnospondyliTemnospondyliTemnospondyli is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent...
- Monophyletic within lepospondyliLepospondyliLepospondyli are a group of small but diverse Carboniferous to early Permian tetrapods. Six different groups are known, the Acherontiscidae, Adelospondyli, Aïstopoda, Lysorophia, Microsauria and Nectridea, and between them they include newt-like, eel- or snake-like, and lizard-like forms, along...
- Diphyletic (two separate ancestries) with apodansCaecilianThe caecilians are an order of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly...
within the lepospondyls and salamanderSalamanderSalamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s and frogFrogFrogs 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...
s within the temnospondyli.
Most molecular studies of extant amphibians support monophyly
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
for caecilians, frogs, and salamanders, and the most recent molecular study based on multi-locus data suggest a Late 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"...
- Early 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...
origin of modern amphibians.
External links
- Biology 356 - Major Features of Vertebrate Evolution by Dr. Robert ReiszRobert R. ReiszRobert Rafael Reisz is a Canadian paleontologist and specialist in the study of early amniote and tetrapod evolution.Robert Reisz was born August 27, 1947, in Oradea, Romania. He received his B.Sc. , M.Sc. and Ph.D. from McGill University as Robert L. Carroll’s first doctoral graduate...
, University of Toronto