Retrieval efficiencies of paper-based references in journals and other serials containing 10 scientific names of fossil amphibians were determined for seven major search engines. Retrievals were compared to the number of references obtained covering the period 1895-2006 by a Comprehensive Search. The latter was primarily a traditional library-based search which involved intensive work from 2002-2007. Only a few references originally obtained by search engines were included. Retrieval efficiencies were calculated by comparison to the number obtained through the Comprehensive Search (assumed to be 100%). All percent retrievals were quite low (mean = 11.3%, range = 4.0-22.9%). For all seven search engines combined (duplicate references excluded), the percent retrieval was only 40.7%. There was also retrieval inefficiency and bias of the search engines in: sampling over time, the top five journals containing the most references, the top five most prolific authors, and non-English references. Consequently, all seven search engines were unsatisfactory for retrieval of references for our scientific research. (Contains 2 figures, 5 tables, and 1 note.)