If you've come across this site by searching for information about the evolution of ears and hearing in amphibians, reptiles, mammals and birds through a search engine, you've no doubt found that there are a fair number of articles on the subject. However, most of those articles are published in journals for which a (paid) subscription is required. Unless you have a subscription or have access to one through an institution (ie, a university library) chances are you're not going to read what you're looking for.
While those articles are resources (books are awesome too!) that should be used when doing any serious academic research, it can be frustrating not being able to access information you want right away. That's why I've decided to compile a list of FREE Internet resources about the topic of the evolution of ears and hearing. All links below will be to articles that are posted IN FULL online that do not require any subscription to read. If you have links to any other articles that fit this category please drop me a line in the comments. I will add to this list as I find more articles. Enjoy!
Evolution of Hearing from Amphibians to Mammals - M. P. F. - November 2004
29+ Evidences for Macroevolution - "Intermediate and Transitional Forms - Reptiles - Mammals" - Douglas Theobald - 2004
Cochlear Mechanisms from a Phylogenetic Viewpoint - Geoffrey A. Manley - Proceedings of the National Academy of Sciences, October 2000
Middle Ear Muscles of the Frog - Earnest Glen Wever - Proceedings of the National Academy of Sciences, June 1979
Mechanics of the Exceptional Anuran Ear - Richard L. M. Schoffelen, Johannes M. Segenhout, and Pim van Dijk - Journal of Comparative Physiology. A, Neuroethology, Sensory, Neural, and Behavioral Physiology, April 2008
Frog Auditory Behaviour - David D. Olmsted - 2006
http://www.neurocomputing.org/AuditoryIntro.aspx Note: contains other good pages about hearing in frogs!
Reptile Hearing - Melissa Kaplan - Herp Car Collection - April 2007
More to come!