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Bone Diggers

Anatomy of Thylacoleo

Thylacoleo skeleton

One of Australia's most fantastic beasts, the extinct Thylacoleo carnifex, or "meat-cutting marsupial lion," possessed a host of physical traits unseen in any single creature alive today. These included features especially suited to a carnivorous hunter, including retractable, catlike claws, a kangaroo's tail, and jaw muscles that delivered a bite stronger than a lion's. Altogether, says paleontologist Rod Wells, Thylacoleo resembled something designed by committee. Referring back to the image at right, learn more below about the marsupial lion's singular anatomy and what it reveals of the animal's predatory life in Pleistocene Australia.—Rima Chaddha


Tail  

Tail
Long and powerful, this is a tail befitting an active predator, yet its closest match today is found in one of Australia's most famous herbivores, the kangaroo. The tail contains narrow bones called chevrons that protect the animal's blood vessels at the point where the appendage bends on the ground. This bone structure allows kangaroos to tripod themselves for balance when standing upright (see image at left). Experts believe Thylacoleo used its tail similarly after it caught its prey, freeing its front paws to get a solid grip on its victim as its powerful jaws dealt the deathblow.



Hind leg  

Hind leg
Thylacoleo carnifex held great strength in its legs, but scars indicating that muscles attached low on its thighbones suggest that it probably lacked the flexibility to move at high speed. This has led some paleontologists to posit that the animal carefully stalked its prey like Tasmanian devils and large cats do today, possibly dropping onto its victims from trees. Despite its common name, however, the marsupial lion bears no relation to the big cats. Note: The skeleton image at the top of this page is greatly foreshortened; the hind legs and forelegs are actually the same length.



Hind paw  

Hind paw
Retractable claws and toes adapted for grasping show that the marsupial lion, which is thought to have lived in a shrubby woodland environment, might have climbed trees. Indeed, one of its nicknames is "drop cat" for its possible tactic of dropping onto prey from trees. Similar skeletal structure and dexterity can be seen in arboreal opossums today, giving their paws a handlike appearance, as seen here.



Front leg and forepaw  

Front leg and forepaw
When the great English anatomist Sir Richard Owen first described Thylacoleo in 1859, he called it one of the "fellest and most destructive of predatory beasts." Scientists today, who unlike Owen have articulated fossil skeletons to work with, concur with his assessment. The animal had powerful front legs and large, slashing claws on its thumbs, a trait unseen in any of its distant living herbivorous relatives. And as on its hind paws, Thylacoleo's forepaws had retractable claws, similar to those of a common house cat. The marsupial lion probably used these claws to climb trees and to secure its prey while feeding.



Teeth  

Teeth
Like the koala, Thylacoleo was a diprotodontian. Meaning "two front teeth," the term refers to the two prominent incisors jutting from its lower jaw. It was due in part to this morphology, which formed a forward dental structure analogous to a parrot's beak, that many early experts maintained that Thylacoleo fed mainly if not solely on plants. But modern anatomists disagree. Strong jaw muscles and sharp, shearing premolars gave the marsupial lion what is believed to be the most powerful bite for its size of any known species, living or extinct.



Nasal cavity  

Nasal cavity
Thylacoleo had a sizeable and highly developed nasal cavity, which suggests that—not surprisingly for a predator—it had a strong sense of smell. It would have used this ability to track down its prey and probably also carrion to supplement its diet. In addition, structures in the palate indicate the presence of a specialized organ that could detect chemical scents called pheromones. These compounds help the modern Tasmanian devil (left) and many other animals find mates by enabling males, for one thing, to assess females' reproductive receptiveness.



Brain  

Brain
CAT scans and molds made from the inside of Thylacoleo's skull have allowed researchers to examine the most obvious physical characteristics of the animal's brain. From the size and prominence of the marsupial lion's cerebral lobes, scientists have determined that the animal relied heavily on its keen senses of hearing, sight, and smell. And as with modern predators like the tiger, other physical structures such as Thylacoleo's nasal cavity and the large nerves that led to its eyes support this.



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