While he pursued his formal education, Gidley became an assistant in vertebrate paleontology at the American Museum of Natural History, in 1892. He remained at this job until 1905, after which he joined the United States National Museum as the preparator in the section of vertebrate fossils. In 1908, after the development of the division of vertebrate paleontology, he became the custodian of fossil mammals. Four years later, in 1912, he became an assistant curator at USNM, a position he held until his death.[1]