Fossil Groups


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.Lepospondyl origin of Lissamphibia    B.Temnspondyl origin of Lissamphibia

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.

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.diagram of pedicellate teeth

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. bicuspid tooth section

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.



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