Lissamphibia
| Lissamphibia Temporal range: Early Triassic–present |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Vertebrata |
| Superclass: | Tetrapoda |
| Class: | Amphibia |
| Subclass: | Lissamphibia Haeckel, 1866 |
| Orders | |
Lissamphibia is a biological subclass of animal that includes all recent amphibians. The name derives from the Latin for smooth amphibia.
Extant amphibians fall into one of three orders — the Anura (frogs and toads), the Caudata or Urodela (salamanders and newts), and the Gymnophiona or Apoda (the limbless caecilians).
Though the ancestry of each group is 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.[1]
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[edit] Characteristics
Some, if not all lissamphibia share the following characteristics. Some of these apply to the soft body parts, and hence don't appear in fossils. However, the skeletal characteristics also appear in several types of Palaeozoic amphibians:[2]
- Double or paired occipital condyle
- Two types of skin glands (mucous & granular)
- Fat bodies associated with gonads
- Double-channeled sensory papillae in the inner ear
- Green rods (a special type of visual cell, unknown in caecilians)
- Ribs do not encircle body
- Ability to elevate the eye (with levator bulbi muscle)
- Forced pump respiratory mechanism
- Cylindrical centra (the main body of the vertebra; cylindrical centra are also found in several groups of early tetrapods)
- Pedicellate teeth (the crown of the teeth is separated from the root by a zone of fibrous tissue; also found in some Dissorophoidea; the teeth of some fossil salamanders are not pedicellate)
- Bicuspid teeth (two cusps per tooth, also found in juvenile dissorophoids)
- 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 stapes (ear bones) in most anurans)
- Loss of posterior skull bones (also in Microsauria and Dissorophoidea)
- Small, widely separated pterygoids (also found in Temnospondyli and Nectridea)
- Wide cultriform process of the parasphenoid (also found in some Microsauria (Rhynchonchos) and Lysorophia)
[edit] Relationships and definition
The features uniting the Lissamphibia were first noted by Ernst Haeckel.[2][3] In the early to mid 20th cetury, a bipyletic origin of amphibians (and thus of tetrapods in general) was favoured.[4][5] 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.[6] 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 tetrapods 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 temnospondyli
- Monophyletic within lepospondyli
- Diphyletic (two separate ancestries) with apodans within the lepospondyls and salamanders and frogs within the temnospondyli.[1]
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.[7][8]
[edit] References
- ^ a b Anderson J.S., Reisz R.R., Scott D., Fröbisch N.B., Sumida S.S. (2008). "A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders". Nature 453 (7194): 515–518. doi:10.1038/nature06865. PMID 18497824.
- ^ a b Trueb, William E. Duellman, Linda Trueb ; illustrated by Linda (1994). Biology of amphibians (Johns Hopkins pbk. ed. ed.). Baltimore: Johns Hopkins University Press. ISBN 080184780X.
- ^ Haeckel, E (1866): Generelle Morphologie der Organismen : allgemeine Grundzüge der organischen Formen-Wissenschaft, mechanisch begründet durch die von C. Darwin reformirte Decendenz-Theorie. Berlin
- ^ Säve-Söderbergh, G. (1934). Some points of view concerning the evolution of the vertebrates and the classification of this group. Arkiv för Zoologi 26A: pp 1-20
- ^ von Huene, F. (1956): Paläontologie und Phylogenie der niederen Tetrapoden, G. Fischer, Jena
- ^ Gordon, M.S. and Long, J.A. (2004): The Greatest Step In Vertebrate History: A Paleobiological Review of the Fish-Tetrapod Transition. Physiological and Biochemical Zoology no 77(5): pp 700-719. article
- ^ Sigurdsen T., Green D.M. (2011). "The origin of modern amphibians: a re-evaluation". Zoological Journal of the Linnean Society 162 (2): 457–469. doi:10.1111/j.1096-3642.2010.00683.x.
- ^ San Mauro, D. (2010) A multilocus timescale for the origin of extant amphibians. Molecular Phylogenetics and Evolution 56: 554-561
- Benton, M. J. (2005), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd
- Carroll, RL (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.
- San Mauro, Diego; Miguel Vences, Marina Alcobendas, Rafael Zardoya and Axel Meyer (May 2005). "Initial diversification of living amphibians predated the breakup of Pangaea". American Naturalist 165 (5): 590–599. doi:10.1086/429523. PMID 15795855.
[edit] External links
- Biology 356 - Major Features of Vertebrate Evolution by Dr. Robert Reisz, University of Toronto
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