Temporal range: late Pliocene—late Pleistocene
|Skeleton of a Thylacoleo carnifex in the Victoria Fossil Cave, Naracoorte Caves National Park|
Thylacoleo ("pouch lion") is an extinct genus of carnivorous marsupials that lived in Australia from the late Pliocene to the late Pleistocene (2 million to 46 thousand years ago). Some of these "marsupial lions" were the largest mammalian predators in Australia of that time, with Thylacoleo carnifex approaching the weight of a small lion. The estimated average weight for the species ranges from 101 to 130 kg. 
Pound for pound, Thylacoleo carnifex had the strongest bite of any mammal species living or extinct; a T. carnifex weighing 101 kg (223 lb) had a bite comparable to that of a 250-kg African lion, and research suggests that Thylacoleo could hunt and take prey much larger than itself. Larger animals it may have hunted include Diprotodon spp. and giant kangaroos. It also had extremely strong fore limbs, with retractable, cat-like claws, a trait previously unseen in marsupials. Thylacoleo also possessed enormous hooded claws set on large semiopposable thumbs, which were used to capture and disembowel prey. The long muscular tail was similar to that of a kangaroo. Specialized tail bones called chevrons allowed the animal to tripod itself, and freed the front legs for slashing and grasping.
Its strong forelimbs, retracting claws, and incredibly powerful jaws mean it may have been possible for Thylacoleo to climb trees and perhaps to carry carcasses to keep the kill for itself (similar to the leopard today). Due to its unique predatory morphology, scientists repeatedly claim Thylacoleo to be the most specialized mammalian carnivore of all time. Thylacoleo had vertical shearing ‘carnassial’ cheek–teeth that are relatively larger than in any other mammalian carnivore. Thylacoleo was clearly derived from the diprotodontian ancestry due to the pronounced development of upper and lower third pre-molars which functioned extreme carnassials with complementary reduction in the molar teeth row. They also had canines but they served little purpose as they were stubby and not very sharp.
Thylacoleo was 71 cm (28 in) at the shoulder and about 114 cm (45 in) long from head to tail. The species T. carnifex is the largest, and skulls indicate they averaged 101 to 130 kg (223 to 287 lb), and individuals reaching 124 to 160 kg (273 to 353 lb) were common.
In 2002, eight remarkably complete skeletons of T. carnifex were discovered in a limestone cave under Nullarbor Plain, where the animals fell through a narrow opening in the plain above. Based on the placement of their skeletons, at least some survived the fall, only to die of thirst and starvation.
In 2008, rock art depicting what is thought to be a Thylacoleo was discovered on the north-western coast of the Kimberley. This represented only the second example of megafauna depicted by the indigenous inhabitants of Australia. The image contains details that would otherwise have remained only conjecture; the tail is depicted with a tufted tip, it has pointed ears rather than rounded, and the coat is striped. The prominence of the eye, a feature rarely shown in other animal images of the region, raises the possibility that the creature may have been a nocturnal hunter. In 2009, a second image was found that depicts a Thylacoleo interacting with a hunter who is in the act of spearing or fending the animal off with a multiple-barbed spear. Much smaller and less detailed than the 2008 find, it may depict a thylacine, but the comparative size indicates a Thylacoleo is more likely.
The first Thylacoleo fossil findings, discovered by Thomas Mitchell and described by Richard Owen, consisted of broken teeth, jaws, and skulls. It was not until 100 years later, 1966, that the first nearly-complete skeleton was found. The only pieces missing were a foot and tail. Currently, the Nullarbor Plain of West Australia remains to be the greatest finding site. These fossils now reside at the Australian Museum.  
Marsupial "lion" alludes to the superficial resemblance to the placental lion and its ecological niche as a large predator. Thylacoleo is not related to the modern lion Panthera leo.
Genus: Thylacoleo (Thylacopardus) - Australia's marsupial lions, that lived from about 2 million years ago, during the late Pliocene and became extinct about 30,000 years ago, during the late Pleistocene epoch.
- Thylacoleo carnifex (Pleistocene)
- Thylacoleo crassidentatus lived during the Pliocene, around 5 million years ago and was about the size of a large dog.
T. crassidentatus fossils have been found in southeastern Queensland.
- Thylacoleo hilli lived during the Pliocene and was half the size of T. crassidentatus.
The holotype fossil was found in Town Cave in South Australia. Additional possible specimens have been found at the Bow fossil site by students and staff of the University of New South Wales in 1979.
- "Marsupial munch tops big biters". BBC News. 5 April 2005. Retrieved 25 May 2010.
- NOVA | Bone Diggers | Anatomy of Thylacoleo | PBS
- Extinct Australian "Lion" Was Big Biter, Expert Says
- Roderick T. Wells , Peter F. Murray & Steven J. Bourne (2009) Pedal morphology of the marsupial lion Thylacoleo carnifex (Diprotodontia: Thylacoleonidae) from the Pleistocene of Australia, Journal of Vertebrate Paleontology, 29:4, 1335-1340, DOI: 10.1671/039.029.0424
- Wroe, S., Myers, T. J., Wells, R. T., and Gillespie, A. (1999). "Estimating the weight of the Pleistocene marsupial lion, Thylacoleo carnifex (Thylacoleonidae : Marsupialia): implications for the ecomorphology of a marsupial super-predator and hypotheses of impoverishment of Australian marsupial carnivore faunas". Australian Journal of Zoology 47 (5): 489–498. doi:10.1071/ZO99006.
- BBC News, "Caverns give up huge fossil haul", 25 January 2007.
- Akerman, Kim; Willing, Tim (March 2009). "An ancient rock painting of a marsupial lion, Thylacoleo carnifex, from the Kimberley, Western Australia". Antiquity (journal). Retrieved 11 December 2012.
- Akerman, Kim (December 2009). "Interaction between humans and megafauna depicted in Australian rock art?". Antiquity (journal). Retrieved 11 December 2012.
- Long, J.A., Archer, M., Flannery, T. & Hand, S. (2002). Prehistoric Mammals of Australia and New Guinea - 100 million Years of Evolution. Baltimore: Johns Hopkins University Press. pp. 224pp.
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- PLEDGE. N 1977, A NEW SPECIES OF THYLACOLEO (MARSUPIALIA: THYLACOLEONIDAE) WITH NOTES ON THE OCCURRENCES AND DISTRIBUTION OF THYLACOLEONIDAE IN SOUTH AUSTRALIA