Monday, July 26, 2010

YPM MAM 14547: A Hero Shrew

Whew, I have been away from the blog for a while (was at the 2010 Evolution Meeting and then the 2010 Joint Meeting of Ichthyologists and Herpetologists), but now I am back and will be posting regularly.

To kick things back off, allow me to introduce Scutisorex somereni, a remarkable animal aptly called the "hero shrew". Although unremarkable in appearance (it generally looks like any other shrew), this little creature can support the weight of an adult human on its back without being crushed! I am not sure how this was tested and I'm not exactly sure I want to know, but multiple online sources seem to confirm this fact.

Here is a picture of our specimen, YPM MAM 14547. It was collected in the early 1970's in Cameroon:


Just how does the hero shrew have such heroic strength? It's all in the spine. For its body size, the hero shrew has the largest spine of any animal. And not only is it bulkier than other animals, it is highly modified in quite a few ways that promote its might. For example, while other mammals have 5 vertebrae in their lumbar region (located at the lower spine), the hero shrew has 11 vertebrae there. One part of the spine, the lateral portion of the vertebral arch, has even been completely altered into interlocking bony plates. Here is a picture of the hero shrew's spine in comparison to a "normal" shrew of the genus Crocidura, taken from Cullinane & Bertram 2000:


For more details on the hero shrew's spinal modifications, see this excellent blog post by The Lord Geekington, which is actually where I got most of the info for my post here. Unfortunately, it's unknown what function this super hero spine serves, although there are a couple of hypotheses (see Jonathan Kingdon's East African Mammals, volume IIA, for one). Someone needs to investigate, in my humble opinion!

One more thing before I sign off. Based on experiences I've had with volunteers who have helped out in our Division, it's a common misconception that shrews are rodents. They are not! Shrews (family Soricidae) are not even close relatives to rodents (order Rodentia). Shrews are actually more closely related to bats and whales than they are to rodents! Because of this, shrews and mouse-type rodents represent a great example of convergent evolution, which is the evolution of similar biological traits and forms in unrelated lineages. Another great example of convergent evolution is the wings of birds and bats-- although they both have wings, their wings evolved independently. It is not a trait that they both have through common ancestry.



References:

Cullinane, Dennis M. & Bertram, John E. A. 2000. The mechanical behaviour of a novel mammalian intervertebral joint. J. Anat. 197, pp. 627-634.