There are no transitional forms between amphibians and reptiles.
Seymouria is a classic transitional form between the amphibians and reptiles. Alfred Romer writes of Seymouria that
it exhibits such a combination of amphibian and reptilian characters that its proper position in the classification of vertebrates has been much disputed. (Romer 1966:94)
and that Seymouria
seems to be an anthracosaurian which stands almost exactly on the dividing line between amphibians and reptiles; we have here a demonstration of the fact that there is no clear-cut distinction between the two classes in skeletal structures. (Romer 1966:95)
Colbert and Morales have equally good things to say about the seymouriamorphs:
Here, we see the effects of a rather well-documented paleontological record. With such a record at hand the divisions between groups break down. The evidence of the seymouriamorphs indicates, too clearly for the peace of mind of those students who wish to categorize animals within neat boundaries of classification, that evolution is a continuum. (Colbert and Morales 1991:86-89)
Colbert EH and Morales M. 1991. Evolution of the Vertebrates: A History of the Backboned Animals Through Time: Fourth Edition. New York: Wiley-Liss.
Romer A. 1966. Vertebrate Paleontology. Chicago: University of Chicago Press.
Last updated: 21 Mar 2008
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