Richard Lydekker (/lɪˈdɛkər/; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history.

He was responsible for the cataloguing of the fossil mammals, reptiles, and birds in the Natural History Museum (10 vols., 1891).

In 1896 he delineated the biogeographical boundary through Indonesia, known as Lydekker's Line, that separates Wallacea on the west from Australia-New Guinea on the east.

Along with Wallace's Line and others,[7] it indicates the definite effect of geology on the biogeography of the region, something not seen so clearly in other parts of the world.

[8] Lydekker attracted amused public attention with a pair of letters to The Times in 1913, when he wrote on 6 February that he had heard a cuckoo, contrary to Yarrell's History of British Birds which doubted the bird arrived before April.