| Lissamphibia | |
|---|---|
 | |
| Emerald glass frog (Centrolene prosoblepon) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Subclass: | Lissamphibia Haeckel, 1866 |
| Subgroups | |
TheLissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group oftetrapods that includes all modernamphibians. Lissamphibians consist of three living groups: theSalientia (frogs and their extinct relatives), theCaudata (salamanders and their extinct relatives), and theGymnophiona (the limblesscaecilians and their extinct relatives).
Salientians and caudatans are likely more closely related to each other than to caecilians. The nameBatrachia is commonly used for the clade combining salientians and caudatans. A fourth group, theAllocaudata (also known asAlbanerpetontidae) is also known, spanning 160 million years from theMiddle Jurassic to theEarly Pleistocene, 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 asTemnospondyli,Lepospondyli,Embolomeri, andSeymouriamorpha.[1] Most scientists have concluded that all of the primary groups of modern amphibians—frogs,salamanders andcaecilians—are closely related.
Some writers have argued that the earlyPermiandissorophoidGerobatrachus hottoni is a lissamphibian.[2] If it is not,[3] the earliest known lissamphibians areTriadobatrachus andCzatkobatrachus from theEarly Triassic.[4][5]
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:[6]
The features uniting the Lissamphibia were first noted byErnst Haeckel, even though in Haeckel's work, Lissamphibia excluded thecaecilians.[6][11] Nevertheless, Haeckel considered the caecilians to be closely related to what he called Lissamphibia (gr. λισσός, smooth), which is now called Batrachia and includesfrogs andsalamanders. In the early to mid 20th century, a biphyletic origin of amphibians (and thus oftetrapods in general) was favoured.[12][13] In the late 20th century, a flood of new fossil evidence mapped out in some detail the nature of the transition between theelpistostegalid fish and theearly amphibians.[14] Mostherpetologists andpaleontologists, 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 ismonophyletic as well. The origin and relationships of the various lissamphibian groups both with each other and among other earlytetrapods remain controversial. Not all paleontologists today are convinced that Lissamphibia is indeed a natural group, as there are important characteristics shared with some non-lissamphibianPalaeozoic amphibians.
Currently, the two prevailing theories of lissamphibian origin are:
One of the hypotheses regarding their ancestors is that they evolved bypaedomorphosis and miniaturization from early tetrapods.[16][17]
Molecular studies of extant amphibians based on multiple-locus data favor one or the other of the monophyletic alternatives and indicate aLate Carboniferous 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.[4][18][19]
The stem-caecilianFuncusvermis, described in 2023, retained manydissorophoid temnospondyl features, supporting a monophyletic Lissamphibia within clade Temnospondyli.[20]
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