The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of that includes all modern . Lissamphibians consist of three living groups: the Salientia ( and their extinct relatives), the Caudata ( and their extinct relatives), and the Caecilian (the limbless and their extinct relatives).
Salientians and caudatans are likely more closely related to each other than to caecilians. The name Batrachia is commonly used for the clade combining salientians and caudatans. A fourth group, the Allocaudata (also known as Albanerpetontidae) is also known, spanning 160 million years from the Middle Jurassic to the Early 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 as Temnospondyli, Lepospondyli, Embolomeri, and Seymouriamorpha.
Some writers have argued that the early Permian dissorophoid Gerobatrachus hottoni is a lissamphibian.
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:
(1994). 080184780X, Johns Hopkins University Press. 080184780X
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Double or paired occipital condyles
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Two types of (mucous and granular)
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Fat bodies associated with
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Double-channeled sensory in the inner ear
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(a special type of visual cell, unknown in caecilians)
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do not encircle body. In anurans the ribs are fused to their vertebrae, except in the suborder Archaeobatrachia which still has free ribs.
[ Biology of Amphibia]
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Ability to elevate the (with the levator bulbi muscle)
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Forced-pump respiratory mechanism, the primitive breathing system also found in labyrinthodontia
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Cylindrical centra (the main body of the ; cylindrical centra are also found in several groups of early )
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Pedicellate teeth (the crowns of the teeth are separated from the roots by a zone of fibrous tissue; also found in some Dissorophoidea; the teeth of some fossil are not pedicellate)
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Bicuspid teeth (two cusps per tooth, also found in juvenile Dissorophoidea)
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Batrachian operculum (small bone in the skull, linked to shoulder girdle by the opercularis muscle; perhaps involved in hearing and balance; absent in caecilians, fused to the otic capsule in some salamanders. This may have been lost in caecilians, or it may be a synapomorphy of Batrachia.
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Loss of posterior skull bones (also in Microsauria and Dissorophoidea)
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Small, widely separated (also found in Temnospondyli and Nectridea)
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Wide cultriform process of the parasphenoid (also found in some Microsauria ( Rhynchonkos) and Lysorophia)
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Presence of ampullae of Lorenzini in some salamanders and caecilians, but never in frogs
[ Chapter 41 - Electroreceptors and Magnetoreceptors][ The Evolution of Amphibian Photoreception]
Relationships and definition
The features uniting the Lissamphibia were first noted by
Ernst Haeckel, even though in Haeckel's work, Lissamphibia excluded the
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[Ernst Haeckel (1866), Generelle Morphologie der Organismen : allgemeine Grundzüge der organischen Formen-Wissenschaft, mechanisch begründet durch die von Charles Darwin reformirte Descendenz-Theorie. Berlin] Nevertheless, Haeckel considered the caecilians to be closely related to what he called Lissamphibia (gr. λισσός, smooth), which is now called Batrachia and includes and . In the early to mid 20th century, a biphyletic origin of amphibians (and thus of in general) was favoured.[von Huene, F. (1956) Paläontologie und Phylogenie der niederen Tetrapoden, G. Fischer, Jena] In the late 20th century, a flood of new fossil evidence mapped out in some detail the nature of the transition between the Elpistostegalia and the Ichthyostegalia.
Currently, the two prevailing theories of lissamphibian origin are:
One of the hypotheses regarding their ancestors is that they evolved by Neoteny and miniaturization from early tetrapods.
Molecular studies of extant amphibians based on multiple-locus data favor one or the other of the monophyletic alternatives and indicate a Late 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.
The stem-caecilian Funcusvermis, described in 2023, retained many Dissorophoidea temnospondyl features, supporting a monophyletic Lissamphibia within clade Temnospondyli.
Bibliography
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Michael Benton (2005), Vertebrate Palaeontology, 3rd ed. Blackwell.
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Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.
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