Owen's original description of Echidna ramsayi, later synonymized as Megalibgwilia ramsayi, consisted entirely of a detailed look at the broken left humerus of one of the "giant" animals. Eventually crania and postcranial remains were added to the descriptive list for this single species. All of the descriptions of M. ramsayi have amounted to a fairly complete picture of this first species of the genus. The second species, M. robusta, was described by William Sutherland Dun in 1896 and consisted of mostly complete remains. Megalibgwiliarobusta is the oldest known echidna and, despite being known as a "giant echidna", is slightly smaller than the largest known monotreme of Western Australian; Zaglossus hacketti. Contemporaries of Zaglossus, the two species of Megalibgwilia were geographically separated from one another and their larger cousins in Western Australia. Megalibgwilia ramsayi appears to have been prominent across mainland Australia and extended to Tasmania whereas M. robusta has been restricted, so far, according to fossil remains, to New South Wales. The two species possessed snouts that are more well suited to probing and grabbing insects than grasping and probing for worms like the Zaglossus group of echidnas. As contemporary species, Megalibgwilia and Zaglossus may have possessed overlapping ranges, making diverse diets for the two groups of animals important in minimizing competition for food sources.