The 1993 Ig Nobel Prize in literature was awarded to Eric Topol, R. Califf, F. Van de Werf, P. W. Armstrong, and their 972 co-authors, for publishing a medical research paper which has one hundred times as many authors as pages. That study was in The New England Journal of Medicine,]
Now, seventeen years later, the journal Nature has published a study that has approximately 57,000 co-authors. That study is:”Predicting protein structures with a multiplayer online game,” Seth Cooper, Firas Khatib, Adrien Treuille, Janos Barbero, Jeehyung Lee, Michael Beenen, Andrew Leaver-Fay, David Baker, Zoran Popović & et al., Nature, vol. 466, August 5, 2010, pp. 756-60.
Do your own calculations about interesting author/page ratios.
BONUS: Here are links to lots of reports (some of which put the co-author count at about 75,000) about the report.