Not really a 'new' species, since it was described in 1926. It validates the opinion of the great mammal-taxonomist Michael Rogers Oldfield Thomas (1858-1929), who first described this wallaby as a distinct taxon in the following article:
Thomas, O. (1926) - 'Two new rock-wallabies (Petrogale) discovered by Capt. G. W. Wilkins in northern Australia.' Annals & Magazine of Natural History 17, p.184–187.