Its cat-like appearance owes something to the theory that T. carnifex was descended from the Burryamids, or Pygmy Possums, which are native to the mountains of S.E. Australia. Hence an arboreal reconstruction with leopard-like appearance is presented. An alternative interpretation has thylacoleonids arising from Vombatid stock. In this case they would have been more closely related to modern day wombats than to possums. That ancestry would, presumably, leave them looking not quite so feline in appearance. The reader should consult the reference material for further exposition on the question of Thylacoleo's ancestry.
The dentition of this animal was unique. It had no canine teeth
as do placental predators like wolves or lions. Instead it was equipped
with very large incisors and extremely specialised carnassial teeth.
These had become blade-like cutting edges, two pairs only being positioned
on the upper and lower jaws.
It has been asserted that T. carnifex's dentition represents the most extreme specialisation of any known mammalian carnivore. The reader is directed particularly to references #2 & #3 for a detailed discussion.
The front paws of T. carnifex were equipped with a partly opposable thumb. The terminal phalanx of the thumb sported an impressively large, curved claw, while the other digits had smaller claws. The rear feet were equipped with similarly opposable thumbs. It's probably true to say that this was an animal equipped with four hands, rather than paws, and that it almost certainly was primarily an arboreal hunter. However, fossil specimens have been unearthed in areas which were open plains when the animal lived. So it appears to have been resourceful enough to make a living with or without a forest habitat.
Variation in the size of fossil remains are usually interpreted to mean that males of the species were bigger than females. Sexual dimorphism is common in many mammalian species, for instance kangaroos, lions and seals. It generally indicates a breeding system where males must defeat and dispossess other more dominant males for access to females. In such species, mature males are often fewer in number than breeding-age females.
Generally speaking, fossil T. carnifex presents as a large animal which exhibited a wide range in body size. Fossil evidence suggests that an average individual would have weighed about 45 kg (Ref #2). The largest specimens, which were just a shade smaller than the African lioness, Panthera leo, appear to have lived in south-eastern Australia.