McCallum (born December 26, 1968 in Maywood, Illinois) is an American environmental scientist, conservationist, herpetologist, and natural historian and is known for his work on the Holocene Extinction.
He is also a co-founder of the herpetology journal, Herpetological Conservation and Biology.
His research has been covered by David Attenborough, Discover Magazine, and other media outlets.