Also, aren't we able to find the (11 million year old) fossil remains of any other creature that's not extinct -- such as a cat, bird, or dog -- for the purpose of refining our predictions based on fossil records?
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WELL, I'd say that wikipedia 'fossils' information can clear that up. Here's what they have to say:

Rarity of fossils

Because fossilization requires the relatively quick preservation of bodily remains, fossils are relatively rare. Fossilization favors big organisms with hard body parts, organisms that were widespread and organisms lived for a long time. Small, soft bodied organisms living in small areas and who did not live for a long time (Ex. they became extinct or they evolved quickly, see punctuated equilibrium for a better explanation) are almost impossible to find fossils of. Geological processes such as erosion and subduction also destroy many fossils. All these reasons make fossils somewhat rare.

So perhaps the rat was just a very unusual fossil find? And a cat would be difficult to locate?

RE: Science & Technology at Scientific American.com: Laotian Rodent Proves Living Fossil