Ammonoids are among the best of index fossils and are particularly useful for intercontinental correlations. Five major ammonoid zones are recognized in the Permian, all of which are of world-wide significance. In Texas and northern Mexico the Permian is particularly well developed and is abundantly fossiliferous, and the section in this area serves well as a standard for the rest of the world.
Proceedings of the Iowa Academy of Science
©1939 Iowa Academy of Science, Inc.
Miller, A. K. and Furnish, W. M.
"Permian Ammonoid Zones,"
Proceedings of the Iowa Academy of Science, 46(1), 251-251.
Available at: https://scholarworks.uni.edu/pias/vol46/iss1/62