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Journal Article

The Paleozoic Relatives of Lissamphibians

Andrew R. Milner
Herpetological Monographs
Vol. 7 (1993), pp. 8-27
Published by: Allen Press on behalf of the Herpetologists' League
DOI: 10.2307/1466948
Stable URL: http://www.jstor.org/stable/1466948
Page Count: 20

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Topics: Herpetology, Amphibians, Monographs, Skull, Genera, Teeth, Vertebrae, Monophyly, Taxa, Fossils
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The Paleozoic Relatives of Lissamphibians
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Abstract

Recent theories of relationship between the living and Paleozoic amphibians are discussed. The clade Amphibia, incorporating the crown-group Lissamphibia, also includes the Nectridea, Colosteidae, Microsauria and the temnospondyls. The Nectridea and Colosteidae may form the sister clade to the clade comprising the Microsauria, the temnospondyls and the Lissamphibia. The Nectridea are a distinct clade of Permo-Pennsylvanian dwarf amphibians and are not of polyphyletic origin from within the temnospondyls, nor are they closely related to lissamphibians. The balance of evidence favors a monophyletic origin of all lissamphibians from within the temnospondyls but the number of character states involved is not so great that this theory can be considered robust. The alternative possibility that gymnophionans are microsaur derivatives is less well supported but remains open. If the Microsauria formed the stem-group to the Gymnophiona, this would not violate the monophyly of the living amphibians or of lissamphibian soft-anatomy characters, although to extend the Lissamphibia to include temnospondyls and microsaurs would be unacceptable. Within the temnospondyl grade of evolution, the only two families that are plausible lissamphibian relatives are the Amphibamidae and the Branchiosauridae. Each shares a few different character states with the Lissamphibia but the Amphibamidae share more character states and also show nesting of derived character states towards the lissamphibian condition. While the Branchiosauridae were perceived as completely neotenous, they were less likely to be the stem-group of the Lissamphibia than the Amphibamidae, but the recent discovery of metamorphosed branchiosaurids will undoubtedly alter this viewpoint.

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