He proposed that dental characters are expressed in morphogenetic gradients along the dentition, which could therefore be used to study evolution.
He was born on 19 July 1912 in Lewisham, London, son of a civil servant, Herbert Butler, and his wife Amy.
He retired at 60, and as an emeritus professor turned to full-time research, much of it done at the Natural History Museum, London.
He later got interested in tertiary mammals from East-Africa and the fauna of the Olduvai Gorge, on which he worked with Louis Leakey.
His drawings feature in many of his publications and Royal Holloway College held an exhibition of his watercolours.