Alpheus Hyatt (April 5, 1838 – January 15, 1902) was an American zoologist and palaeontologist.

He briefly attended the Maryland Military Academy and Yale University, and after graduating from Harvard University in 1862, he enlisted as a private in the Massachusetts Volunteer Infantry for the Civil War, emerging with the rank of captain.

He and a colleague founded American Naturalist and Hyatt served as editor from 1867 to 1870.

He also served as curator of the Boston Society of Natural History, where his longtime assistant was his former student Jennie Maria Arms Sheldon, and he established a laboratory at the Norwood-Hyatt House in 1879[1] for the study of Marine Biology in Annisquam, Massachusetts.

Hyatt studied under Louis Agassiz and was a proponent of Neo-Lamarckism with Edward Drinker Cope.