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Did the “Marsupial Lion” Climb Trees?



Restoration of the skull of Thylacoleo. From The Ancient Life History of the Earth.

ResearchBlogging.org

Thylacoleo was one strange mammal. A close relative of living koalas, kangaroos, and wombats, the largest species of Thylacoleo were lion-sized carnivores that stalked the Australian continent between 2 million and 45 thousand years ago. Despite its popular nickname “marsupial lion”, however, Thylacoleo was quite different from any feline predator. Even though its long forelimbs were tipped with retractable claws its skull more closely resembled that of a koala, with curved incisors set in front of a pair of cleaver-like shearing teeth. This resemblance caused some naturalists to believe that Thylacoleo was just another herbivore, but more recent studies have confirmed that it most certainly was a carnivore.

But what kind of predator was Thylacoleo? Some have proposed that it hunted down prey and then dragged it into the trees, as a leopard does, while others have argued that it was more lion-like in habit. The entire argument hinges upon whether Thylacoleo could climb trees or not, which in turn rests on our understanding of the predator’s anatomy. The details of the skeleton of Thylacoleo, particularly its hands and feet, can provide paleontologists with clues as to what it was capable of. Unfortunately scientists have had to cope with an incomplete understanding of the hind feet of Thylacoleo for years, but a recent discovery from an Australian cave has brought new information to the discussion. As reported by paleontologists Roderick Wells, Peter Murray, and Steven Bourne in the latest issue of the Journal of Vertebrate Paleontology a complete hind foot of Thylacoleo has finally been found.

In June 2005 the owners of Henschke’s Quarry in Naracoorte, Australia contacted scientist Steven Bourne about some fossils they had found in a cave on their property. When scientists began to excavate it they found, among other things, the incomplete-yet-articulated remains of several Thylacoleo carnifex, including parts of a tail and a complete hind foot. These fossils form the basis of the new study.



The restored left foot of Thylacoleo carnifex. (From Wells et al, 2009)

When put together the complete left hind foot of Thylacoleo is quite different from that of a cat. Cats are digitigrade, or they are standing up on their “tippy toes” all the time. The foot of Thylacoleo, though, is plantigrade, or like ours in that the metatarsal bones support part of the foot that touches the ground (to pick an example among carnivores, bears also have plantigrade feet). The feet also have a bit of a curve to them; in the restored foot the bones around the ankle articulation slant to the left while the metatarsal and toes slant to the right.

The core of the paper is the descriptive work the scientists carried out (which includes sentences such as “The second tarsal row includes the cuboid, navicular, and the endo-, meso-, ento-cuneiforms,” which brings back memories of human anatomy class), but it is what the feet can tell us about the life of Thylacoleo that is most interesting. While the parts of the foot around the ankle were most similar to the same bones in wombats and phalangers (herbivorous relatives of Thylacoleo in the group Diprotodontia) the toes were well-suited to grasping and digging into pliable surfaces. The curvature of the foot and the retractable claws that tipped the toes of Thylacoleo would have helped it to grasp tree trunks or grab onto the torso of its prey, but what did it really do?



The restored left foot of Thylacoleo carnifex, shown as if it were grasping a tree trunk or the trunk of a prey animal. (From Wells et al, 2009)

The traits that made Thylacoleo a formidable killer may have also helped it in climbing (and vice versa). As the authors state, it appears that Thylacoleo had feet that certainly could have supported it and helped to push it up into trees, and these anatomical peculiarities would have also been useful in handling prey. Thylacoleo certainly could have climbed up into trees if it wanted to, and the authors promise that they have uncovered other new anatomical evidence that suggest that the marsupial predator did climb trees. I certainly look forward to reading more about this as-yet-unpublished evidence.

Wells, R., Murray, P., & Bourne, S. (2009). Pedal Morphology of the Marsupial Lion
(Diprotodontia: Thylacoleonidae) from the Pleistocene of Australia
Journal of Vertebrate Paleontology, 29 (4), 1335-1340 DOI: 10.1671/039.029.0424

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