 In his last years Tillyard was much interested in some work on supposed pre-Cambrian fossils in South Australia which was done in co operation with Edgeworth David.The account of their investigations is contained in "Memoir on Fossils of the late Pre-Cambrian", by David and Tillyard, published in 1936.Tillyard was one of the most influential workers on the fossils of the Elmo Permian deposits, believing that the key to the true classification of insects would be found in these early fossils.