Joseph Leidy, American paleontologist and author (b. 1823)
Joseph Mellick Leidy (September 9, 1823 – April 30, 1891) was an American paleontologist, parasitologist and anatomist.

Leidy was professor of anatomy at the University of Pennsylvania, later was a professor of natural history at Swarthmore College and the director of scientific and educational programs at the Wagner Free Institute of Science. His book Extinct Fauna of Dakota and Nebraska (1869) contained many species not previously described and many previously unknown on the North American continent. At the time, scientific investigation was largely the province of wealthy amateurs.

The Leidy Glacier in northwest Greenland was named by Robert Peary after him.