Sunday, June 17, 2007

The Palaeozoic Ancestry of Salamanders, Frogs and Caecilians

The Palaeozoic Ancestry of Salamanders, Frogs and Caecilians. 2007. Robert L. Carroll. Zoological Journal of the Linnean Society 150: 1-140.

Triadobatrachus massinoti, a primitive frog-like amphibian from the Lower Triassic of Madagascar by Pavel Říha
Abstract [edit]: The relationships of frogs, salamanders, and caecilians (Gymnophiona) with one another and with the vast assemblage of Palaeozoic amphibians remain highly contentious phylogenetic problems. Cladistic analyses support a common ancestry of the three modern orders, but fail to achieve a consensus regarding their affinities with Palaeozoic amphibians.

Making use of the numerous derived characters that are expressed in either the larvae or adults of extant salamanders, frogs, and caecilians provides the basis for recognizing a nested sequence of synapomorphies that support a common ancestry of salamanders and anurans with temnospondyl labyrinthodonts to the exclusion of caecilians. The larvae of Carboniferous and Permian temnospondyl labyrinthodonts provide strong evidence for their being members of the stem group of urodeles. This is based primarily on the great similarity in the sequence of ossification of the bones of the skull and appendicular skeleton, but is also supported by detailed similarities of the hyoid apparatus.

Recognition of a sister-group relationship between Permo-Carboniferous branchiosaurids and crown-group salamanders makes it possible to determine the sequence of changes in the anatomy and ways of life that occurred during the origin of urodeles, and to determine their time of divergence relative to that of frogs and caecilians.
Anyone with an interest in the evolutionary history of amphibians will want to get a copy of Bob Carroll’s latest monograph.