Hey, what are your thoughts on R.O.U.S. ? Do you think they exist? If so, what counts as one?
Well, you have to determine what’s an unusual size for a rodent first! At one end of the scale, you have the capybara; at the other, you have the dwarf three-toed jerboa, which is less than two inches long from nose to the base of the tail. That’s a pretty big gamut of sizes!
However, if you look at islands, you’ll start to see rodents that are definitely outliers for their taxa- they really are of unusual size. One of these is the Gough Island house mouse, a population of Mus musculus that lives on Gough Island and feeds almost exclusively on petrel chicks. Gough Island is a volcanic island that’s extremely resource-poor. For petrels, that’s fine, as they consume fish, but for the mice, which are an introduced species, there’s not a lot to eat- except the baby petrels. Larger mice had an advantage and went on to produce larger offspring- as a result, the house mice of Gough Island weigh about 1.2 to 1.8 ounces. This is absolutely enormous for a mouse; house mice usually weigh around 0.7 ounces. So the Gough Island house mouse (on the left, next to a mainland house mouse) is definitely a rodent of unusual size!
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