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BIOLOGY:
- ANATOMY -
SKULL AND SKELETON: POST-CRANIAL SKELETON (page 3)
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    In a recent paper entitled: "The predatory behaviour of the thylacine: Tasmanian tiger or marsupial wolf?" published online in "Biology Letters" (Figueirido and Janis 2012), comparison was made between the elbow joint of the thylacine and those of dog-like and cat-like species.  The researchers state:

    "An established morphological indicator of predatory behaviour can be found in the elbow joint, specifically in the shape of the distal humerus.  Pursuit carnivores have a restricted range of motion at the elbow, while less cursorial predators retain the ability to supinate the forearm, and may use the forelimb to grapple with their prey".

    The researchers used geometric morphometrics to explore the morphology of the distal humerus of placental carnivores of known predatory behaviour.  A total of 103 humeri of adult individuals belonging to 32 species of mammals, including eight thylacines, were used in the study.  They found that in the thylacine, the articular surface of the distal humerus was wider and more rectangular in shape, and therefore more akin to that of feline predators such as the tiger than that of the wolf or fox, whose articular surface tended to be squarer.

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comparison of the shape of the distal humerus in the thylacine, tiger, wolf and fox
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Comparison of the shape of the distal humerus in the thylacine, tiger, wolf and fox. Photos: Borja Figueirido (specimens from the American Museum of Natural History).
distal humerus of the thylacine
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Distal humerus of the thylacine.
Photo: ITSD 4th Revision 2011.
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    The Brown University press release notes: 

    "They (Figueirido and Janis) knew from previous research that the elbow joint was a clue to predator habits, as it showed whether the animal was built for flexibility and dexterity in handling prey or for chase and speed in tracking down the next meal.  Examining the bones, they found that the thylacine's humerus, or upper arm bone, was oval and elongated at the end closest to the elbow, implying that the animal's forearm bones, the radius and ulna, were separate.  That means the Tasmanian tiger would have been able to rotate its arm so that the palm faced upwards, like a cat.  The distal humerus on dog-like animals, such as dingoes and wolves, is 'more squared-up and shorter,' Janis said.  This indicates the radius and ulna were closer together in these species, reflecting that these animals' hands are more fixed in the palm-down position.  In terms of hunting, the increased arm and hand movement would have given the thylacine a greater capability of subduing its quarry after a surprise attack.  Since dingoes and other dog-like creatures have less latitude in arm-hand movement, that helps explain why these animals hunt by pursuit and in packs, rather than in an ambush setting, the researchers note".

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skeletal thylacine pes (foot) and manus (hand)
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At left, the skeletal thylacine pes (foot), and at right, the manus (hand).
Photo: International Thylacine Specimen Database 4th Revision 2011.
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    Figueirido and Janis conclude: 

    "We propose that the thylacine was more of an ambush predator than the living Grey wolf, which is often considered as its ecological counterpart.  We provide quantitative support to the suspicions of earlier researchers that the thylacine was not a pursuit predator, thus bringing into question the degree of ecomorphological convergence between thylacines and wolves.  In fact, the predatory behaviour of the thylacine was probably closer to that of ambushing felids than to that of large pursuit canids.  Consequently, at least in terms of the postcranial anatomy, the vernacular name of 'Tasmanian tiger' may be more apt than that of 'marsupial wolf'".

    No discussion on the post-cranial skeleton would be complete without brief mention of the structure of the thylacine's manus or hand; the external features of which are discussed in detail in the External Anatomy subsection.

    As can be seen from the below image of a thylacine feeding at the London Zoo, the digits number 5, and they are splayed.  In a dog, only 4 digits would be evident, and these would be rather tightly bound together by webbing.  The 5th digit in the dog is commonly referred to as the "dew claw"; it is vestigial, and unlike the thumb of the thylacine, does not participate in weight-bearing.

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film still of a thylacine at the London Zoo / skeletal thylacine manus
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Still from a motion picture film of a thylacine feeding at the London Zoo.
Note the 5 digits of the hand or manus.  Courtesy: Zoological Society of London.
Inset - skeleton of manus.  Photo: International Thylacine Specimen Database 4th Revision 2011.
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References
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back to: Post-cranial Skeleton (page 2) return to the subsection's introduction forward to: Anatomical Diagrams of the Skull


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