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Mammal record breakers

What a backbone!

The Hero Shrew Scutisorex somereni has the strangest, and strongest, backbone of any mammal, size for size. It has long been known that the Mangbetu natives in the Congo forests demonstrate this fact by standing on the animal, without killing it, but how and why it should have such a backbone remain mysteries.

Externally, the Hero Shrew looks much like any other white-toothed shrew; a woolly grey coat, with a thick tail and large ears. As shrews go it is large, 70-113 g, and it moves with more of a loping gait than other shrews, but it is its remarkable backbone that has attracted most attention. Each vertebra, but especially the lumbar vertebrae between the rib cage and hips, is a great corrugated cylinder, with a complex of interlocking tubercles articulating to the previous and succeeding vertebrae. In total, the vertebral column is nearly 4% of body weight, compared to between 0.5% and 1.6% in other small mammals (Cullinane et al. 1998). The ribs are also much thicker than in other small mammals, yet the limb bones are about the same size. Along with the peculiar spine, the spinal muscles are highly modified, the transverse muscles being reduced (their resistance to twisting being performed instead by the complicated vertebrae?) but the muscles of flexion and extension being well developed.

So why the funny bones? It must be emphasised that the vertebrae are not simply enlarged versions of the bones in other shrews; they are uniquely complicated in their anatomy, and no other shrew has anything that might hint at how or why the change came about. The life style as so far understood gives no clues either. The Hero Shrew does not burrow, or hunt through leaf litter, or turn over logs, in some obviously peculiar way, so far as the limited observations of them in captivity show. They feed on earthworms, insects and small frogs, apparently, though they will eat mammal or bird flesh if offered. The animal does show a somewhat snakelike movement, and it seems that its backbone is adapted to flex downwards and resist compression in recovering - as though it should be lifting large weights in its teeth, or pulling earthworms out of their burrows. An early boy scout, extracting thorns from elephant's hooves?

For more detailed information:

Kingdon, J. 1974 East African Mammals Vol IIA. (Academic Press, London)

Cullinane, D.M., Aleper, D. & Bertram, J.E.A. 1998. The functional and biomechanical modifications of the spine of Scutisorex somereni, the hero shrew: skeletal scaling relationships. J. Zool. Lond. 244: 447-452.

Cullinane, D.M. & Aleper, D. 1998. The functional and biomechanical modifications of the spine of Scutisorex somereni, the hero shrew: spinal musculature. J. Zool. Lond. 244: 453-458.


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