ven diagram of amphibians, fish and reptiles?

Answer 1

With biological features, it is well overlapping over each other.

It is better to create a phylogenetic tree.

Check out these sites for more information:
http://www.msnbc.msn.com/id/4638587/;
http://www.tolweb.org/Amniota/14990 - Explore further!;
http://cas.bellarmine.edu/tietjen/images/general_overview_of_animal_phyla.htm;
http://library.thinkquest.org/19012/treeolif.htm