We have already seen that the Pleistocene period, which dates back 2 million years to the close of the Pliocene, was dominated by the megafauna, chiefly the marsupial giants. Yet there were small species too, and the recent fossil discoveries at Riversleigh, in Queensland’s north-west, have added greatly to our knowledge of Australian animal life of this time, stretching back to the Oligocene period, over 23.3 million years ago.
The Thylacinids are well represented in the Riversleigh deposits, where the fossil record is diverse, ranging from tiny, specialised forms to large, more primitive kinds. Before the Riversleigh discoveries, the thylacinid fossil record of the Tertiary era was very poor.
The Tertiary includes our present Holocene period, stretching back through the Pleistocene, Pliocene, Miocene, Oligocene, Eocene and Palaeocene, which covers a time span of 65 million years.
It was in late Miocene deposits at Alcoota, Northern Territory, that the earliest Thylacine species was found, this was Thylacinus potens, the “powerful” Thylacine, and is the largest known species, and appears to have preceded the Tasmanian Thylacine by about 4 to 6 million years. It is known from one 8-10 million years old fossil deposit near Alice Springs.
The fossil remains show that Thylacinus potens was a massive-built, powerful animal, with a robust snout and large teeth, suggesting it had a bite as powerful as a Rottweiler dog. The Tasmanian Tiger, or Thylacinus cynocephalus, the species with which this chapter is concerned, due to modern-day sightings reports both in Tasmania and on the mainland, is probably as old as Thylacinus potens.
At last count, palaeontologist Jeanette Muirhead has identified five different Thylacines from the Riversleigh Oligo-Miocene fossil faunas, these species range from one as small as a large domestic cat to one perhaps three-quarters the size of a German Shepherd Dog. The smallest is only slightly smaller than the largest of Riversleigh’s dasyurids - small mammalian carnivores of the Oligo-Miocene periods.
Dasyurids, numbats and thylacinds comprise the superfamily Dasyuroidea and the order Dasyuri morphia, all of which are dominantly carnivorous or insectivorous. Of the Dasyurimorphians, the ‘extinct’ Thylacinus cynocephalus was the largest; although fossil remains of the late Miocene Thylacinus potens suggest it was a more heavily built animal.
Recently found fragmentary evidence and old eyewitness reports suggest to scientists that the last mainland Thylacines may have died out in the Kimberley region of Western Australia as recently as 80 years ago, and at least 3,000 years ago in the southern half of the mainland. Hitherto this approximate date had been given to its entire mainland disappearance. Perhaps the following reports will one day help to write a new chapter to the Thylacine story.
From isolated regions throughout the Australian mainland, and in Tasmania, where the last officially recognised living individual died in Hobart Zoo in 1936, as well as New Guinea, where fossil remains convince scientists they became extinct 9,920 years ago, people in modern times are claiming to have seen, often at close quarters, living Thylacines.
Heather and I have carried out countless field investigations around Australia since we married in 1972, and interviewed far too many eyewitnesses in our search for the Thylacine, to accept that the species is totally extinct on the Australian mainland.
For one thing, there was my own, personal sighting of a Thylacine outside Blackheath on the Blue Mountains, west of Sydney in 1972; and also the freshly made paw prints of one or more of these creatures found by ourselves and colleagues at another Blue Mountains location in 1983 and 1984, to be discussed later. These tracks were cast and later compared with others made from freshly-made paw prints in Tasmania with which they match up.