Modern Forms
The
Temnospondyli died out in the Early Cretaceous. Whether they left
behind any ancestors is the subject of a very large argument. Some
experts believe that the Lissamphibia, that is all modern forms of
amphibians, originate from the temnospondyls. However some believe that
a seperate group, the Lepospondyli, are responsible for the origin of
the Lissamphibia.
A.
B.
A.
B.Figure A
shows a cladogram representing the lepospondyl theory of Lissamphibian
origins. The Temnospondyli are rooted in the Stem tetrapods and are not
classified as Amphibia.
Figure B
shows the temnospondyl theory of Lissamphibian origins.The cladogram
only shows the Amphibia section and not the Stem-tetrapods as in Figure
A.
Some of the features linking the Temnospondyli and the Lissamphibia are discussed below.
C.
Figure C shows the features present in pedicellate teeth.
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Some of the features linking the Temnospondyli and the Lissamphibia are discussed below.
Pedicellate teeth
Pedicellate teeth only appear in the modern amphibians (Lissamphibia). They also appear frequently in the Temnospondyli and are most apparent in Dolserpeton. While they also appear in a few other Lepsopondyls it has been suggested that the teeth are indicators that the modern amphibians are the descendants of the Lissamphibia.C.
Figure C shows the features present in pedicellate teeth.
Otic Notch
The Otic notch is another feature shared between modern amphibians and the temnospondyls. The otic notch is an area at the back of the skull where a stapes has been found in come individuals. In modern amphibia it comprises part of the ear and it is suggested that the Lissamphibian ear originated in the Temnospondyli and evolved from there.Bicuspid Teeth
Bicuspid teeth are found in almost all modern amphibia. Those that don't have bicuspid teeth generally have a variation on it, i.e. tricuspid or monocuspid. These variations are said to have evolved after the divergence of the groups. Some early temnospondyls, e.g. Dolserpeton, appear to have bicuspid teeth as well as a number of other characteristics found in the Lissamphibia.D. 
Figure D shows a bicuspid tooth in section.
All these characters as well as more anotomically specific characters
have been found in certain individual specimens or species of
lepospondyl. This has brought about a conclusion that the lepospondyls
are the ancestors of the modern amphibia and that the temnospondyls did
not give rise to any further groups. Whether or not this is the correct
conclusion or whether the temnospondyl origin of the lissamphibia is
correct is the subject of a strongly contested debate.Figure D shows a bicuspid tooth in section.
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