The disappearance of the thylacine on the Australian mainland, as well as New Guinea, is generally considered to have been due to the ancient introduction of the dingo (Archer 1974) and New Guinea singing dog, both of which are adapted to living in open country.  Possibly,  the thylacine might have survived in thick forests if these canids had been its sole competitors, but the additional pressure of man's presence was probably critical.  A decline in natural prey on the mainland must also of course be taken into consideration.

. A thylacine at the Hobart Zoo (Domain site).  This image is from a 1928 film.

Evidence gathered by Rolls (1969) shows that at the time of European settlement, kangaroo populations on the mainland were less dense than in Tasmania, and that their numbers only grew after the dingo and Aboriginals had been removed.
 

. This circa 1910-1920 image of two thylacines at the Hobart Zoo (Beaumaris site) was only recently discovered in a collection of old photos.  Possibly, this is the same pair shown here.

Reasons for the decline of the thylacine in Tasmania remain somewhat conjectural.  Beyond absolutely any doubt however, if pressure from direct persecution by man was not fully responsible, it at least put such a severe strain upon the species that it was unable to cope with other pressures.  To deny that shooting and trapping played an extremely significant role in the massive loss of thylacine numbers would be preposterous.  If Guiler's (1961b) informant was correct, however, disease may have been the final, precipitating factor which reduced the Tasmanian thylacine's population to such a dangerously low level.  Whatever the case may be, the thylacine species has suffered irreversible damage due to man's ignorance and stupidity.

    While there were a few individuals who were notable exceptions, the early years of the 20th century were not an era of wildlife conservationists.  Unlike the case with Sarcophilus, which also came under heavy persecution, many within the zoological community feel that there does not appear to have been any breeding nuclei of sufficient size left from which thylacine populations could grow back to their former numbers.  The widespread campaign of poisoning noted by Fleay (1946) and Griffith et al. (1972) likely prevented population recovery.  Its range probably decreased over the two decades following Fleay's expedition, since the areas where Fleay found tracks did not yield anything during Griffith's searches which began in the late 1960s.
 

. Another circa 1910-1920 photo of thylacines which were kept at the Hobart Zoo (Beaumaris site).

    Among the best evidence for the thylacine's continued existence is provided by the Old Davey Track prints (Muir 1961).  Fully described by their discoverers, they were also identified by a qualified zoologist.  Similarly, a number of the many alleged thylacine sightings in Tasmania may indeed be authentic.  Whether the thylacine still survives on the Australian mainland, or even in New Guinea for that matter, remains a topic of even greater controversy.  The existence of mainland thylacines certainly requires definite proof before it can be accepted, but the compilation of all pertinent information, some of which has been presented here, is a necessary prerequisite.  In Tasmania, there are far more alleged sightings than are actually published - over 100 were noted by Griffith et al. (1972).  Tasmania's scientific community should make it a priority to explore and collate these claims.