Career
Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and subspecies for the first time. He was appointed to the Museum Secretary"s office in 1876, transferring to the Zoological Department in 1878. In 1891 Thomas married Mary Kane, daughter of Sir Andrew Clark, heiress to a small fortune, which gave him the finances to hire mammal collectors and present their specimens to the museum.
He also did field work himself in western Europe and South America.
In 1896 when William Henry Flower took control of the department he hired Richard Lydekker to rearrange the exhibitions, allowing Thomas to concentrate on these new specimens. Officially retired from the museum in 1923, he continued his work without interruption.