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labyrinthodontia
Labyrinthodontia (Greek, "maze-toothed") is an extinct amphibian subclass, which constituted some of the dominant animals of late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). The group evolved from lobe-finned fishes in the Devonian and is ancestral to all extant landliving vertebrates. As such it constitutes an evolutionary grade (a paraphyletic group) rather than a natural group (clade). The name describes the pattern of infolding of the dentin and enamel of the teeth, which are often the only part of the creatures that fossilize. They are also distinguished by a heavily armoured skull roof (hence the older name "Stegocephalia"), and complex vertebrae, the structure of which is useful in older classifications of the group.
Because labyrinthodonts do not form a monophyletic group, many modern researchers have abandoned the term. However, some have continued to use the group in their classifications, at least informally, pending more detailed study of their relationships.
==Labyrinthodont traits==
The labyrinthodonts flourished for more than 200 million years. Particularly the early forms exhibited a lot of variation, yet there are still a few basic anatomical traits that make their fossils very distinct and easily recognisable in the field:
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