Bones That Look Like Other Bones: Rodent Week Edition

According to Twitter, last week was #RodentWeek. So here’s another comparative anatomy minipost about some commonly found rodents: squirrels, rats, and mice!

Skulls and mandibles from left to right: squirrel, rat, and mouse.

Now, when it comes to differentiating between these three, size matters. As you can see from the above photo, there’s a huge difference between the skull of a squirrel and the skull of a mouse!

Rats and squirrels may be a toss up, depending on the age and size of the animal – but there’s differences in the shape as well! Personally, I’ve always associated squirrels with a more rounded cranium than rats, who normally have a more flattened skull, but your mileage may vary on that.

Skulls from left to right: Squirrel, rat, and mouse

What will be very difficult is if the only elements available to you are the incisors, or the front teeth. Again, size is beneficial here, as otherwise incisors will more or less look the same across the board for rodents!

Also, take another look at those skulls – lots of similarities between the mouse and rat, less so for the squirrel. And you can kinda see what I mean about the more flattened top of the rat in comparison! There’s a similar elongation that both the rat and mouse share as well.

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Mandibles from top to bottom – squirrel, rat, and mouse

For the most part, identification of rodent remains requires close examination. As you can see above, there are many slight differences between the different rodents, but it requires a bit more study than say, differentiating between a rodent and a frog.  In some cases, complete identification may not be possible without some references on hand!

That said, those incisors are often huge clues that point towards a rodent – if all else fails, at least you might be able to point to that! Those incisors also create a very specific gnaw mark on bones that will help ID the presence of rodents at the site (this will be the topic of a future blog post though!).

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Femurs from top to bottom – squirrel, rat, and mouse

I’ve spent most of this post (as I do with most of these comparative anatomy miniposts) talking about the skulls for identification – to be honest, skulls are usually the easiest part of the body to ID and compare. So here’s something a bit different – let’s quickly look at some long bones of rodents.

As I said previously, rodents require a bit more investigation in differentiating between them. As you can see by the femurs above, there are certainly some differences between a squirrel, rat, and mouse! Compare the straighter edge of the squirrel femur towards the more curved femurs of the rat and mouse, for example.

I hope these miniposts are somewhat helpful for you – obviously a more detailed comparative anatomy post would be much longer, but hey! Maybe one day I’ll write up some manuals – let me know if that sounds interesting to anyone!

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