Mary Cynthia Dickerson was born in Hastings, Michigan. She went to college, supported herself, in an era when it was difficult for a young woman to do so. She attended the University of Michigan, taught high school biology in Michigan and Illinois, then went to the University of Chicago, where she earned a bachelor of science degree in 1897. From 1897 to 1905, she was the head of zoology and botany at Rhode Island Normal School in Providence. She led her students on nature walks and collected observations and specimens. Her first book, Moths and Butterflies (1901), which she illustrated with her photographs, was well received, leading to her next, The Frog Book (1906). She spent 1907 to 1908 as an instructor at Stanford University, then joined the American Museum of Natural History in New York, where she remained for the rest of her career. When the Department of Ichthyology and Herpetology was established in 1909, Mary C. Dickerson became its first and only herpetologist. She also was named associate editor of The American Museum Journal, becoming editor the following year, a position she held until 1920. Under Dickerson's direction, the herpetology collections grew to nearly 50,000 specimens, and in 1920, herpetology was separated from ichthyology and the museum established a new Department of Herpetology with Dickerson as its first curator. She described more than 20 new species of reptiles, and is commemorated in the names of four other lizard species or subspecies. By around 1919, she was showing signs of mental disturbance, and her behavior became erratic; in 1920, she was removed from the museum and placed in the custody of her brother. Later she was placed in a psychiatric institution on Wards Island, where she died at age 57 in 1923.