In the 19th century, a zoological exploration established that wild elephants occurred naturally in a restricted region of northeastern Borneo. The status and taxonomic distinctiveness of the Borneo elephants has been controversial since then. In 1940, Frederick Nutter Chasen considered Bornean elephants as descendants of an introduced stock, and placed them in the subspecies "Elephas maximus indicus". Reginald Innes Pocock having studied specimens in the British Museum of Natural History disagreed in 1943, and placed all Sundaic elephants in the subspecies "Elephas maximus sumatrensis". In 1950, Paules Edward Pieris Deraniyagala described a subspecies "Elephas maximus borneensis", taking as his type an illustration in the National Geographical Magazine.