The enormous upper incisor teeth are well preserved and plainly visible in this specimen of a Thylacoleo skull.  The reddish ochre colouration of this fossil is caused by a thin coating of silt particles rich in iron oxide.  Most of the cave fossils found in South Australia exhibit this feature.  If the encrustation is completely removed, the fossil bone is often surprisingly white, looking not at all that different from recent bone.

Also, wear on the maxillary incisors created a blunted, semi-circular wear surface; in contrast, wear on the mandibular incisors held a sharp triangular outline from which fine, serrated ridges descended.  Examination of the jaw mechanics of the complete Thylacoleo material indicates a possum-like jaw musculature designed for stabbing with the mandibular incisors and slicing with the enormous premolars.  All evidence suggests a carnivorous marsupial of diprotodontid ancestry, not a plant-eater.     The adaptations of Thylacoleo's limb were for climbing and gripping rather than running and walking, while the absence of interlocking canines as a method of holding prey was compensated for by the large, hooded claw of the thumb. Thylacoleo may well have seized prey by grasping it with its powerful hands, then killed it by strangulation or suffocation in a similar manner as do lions and cheetahs (Schaller, 1972); combined use of incisors and premolars would quickly strip the prey's skeleton of hide and flesh.

    Solid evidence of thylacoleonid predation has come from examinations of incised bones initially reported from Queensland (De Vis 1883) and Victoria (Spencer and Walcott, 1912) and more recently from Lancefield in Victoria (Horton et al., 1979;  Horton and Wright, 1981).  Horton and Wright (1981) studied deep v-shaped incisions on ribs and limb bones of kangaroos and made note that 'The Lancefield bones suggest that the species (Thylacoleo) was a meat-eater and give no indication that it was a bone-crusher'.  Their proposition gains support from the absence of completely severed bones in coproloites (scats), characteristic of the bone-eating and crushing Tasmanian devil (Sarcophilus harissi).

What animals were preyed upon by Thylacoleo?  Wells, Horton and Rodgers (1982) note that the animal's size itself makes it an unlikely predator of arboreal species, which are capable of moving through the highest branches with ease.
 

The remains of Thylacoleo are often found in association with those of the extinct leaf-eating kangaroos of the genus Sthenurus.  Possibly, Thylacoleo preyed upon these and other kangaroo species and dragged its prey into trees, as does the leopard, removing it from the reach of scavenging animals such as the Tasmanian devil.  This view harmonizes well with all of the available evidence and provides a niche for a carnivore, which avoids competition with the thylacine (Thylacinus) the only other large predatory Australian marsupial known to have existed.

Mandible section of Sthenurus, a large species of extinct  kangaroo from the Pleistocene epoch.  Could this and  other macropods have been the main prey of Thylacoleo?  This specimen comes from the Wellington Caves of New  South Wales.  Actual length - 125 mm

    Recent findings of fossil material have extended the geographic distribution of Thylacoleo to the Pleistocene deposits of the Lake Eyre Basin; indeed it is present in most Late Pleistocene faunas throughout the whole of the Australian continent.  With the exception of the Victoria Cave Deposit at Naracoorte (Wells, et al., 1984), its numbers are usually low, which is in agreement with an animal filling the niche of top carnivore.  Thylacoleo appears to have vanished along with many of the large marsupial herbivores during a time of great aridity which occurred about 18,000 years ago.  It was a period when the great ice sheets of the northern hemisphere reached their maximum.

    Until quite recently, Thylacoleo carnifex was the only representative of the family Thylacoleonidae, but discoveries in mid-Tertiary sediments of Queensland, the Northern Territory and South Australia (Archer and Wade, 1976;  Archer and Rich, 1982;  Clemens and Plane, 1974;  Pledge, 1977) indicate an older diversification of these fascinating marsupial carnivores (Archer and Dawson, 1982).  Presently, only teeth, skull and jaw fragments are known.  While much smaller in dimension than T. carnifex, species of the Tertiary, such as Wakaleo alcootensis, Wakaleo oldfieldi, Wakaleo vanderleuri (mid-Miocene) and T. hill (? Pliocene), all exhibit the same characteristic slicing premolars featured in their much larger Pleistocene relative.