Bones That Look Like Other Bones: A MiniPost About Rodents and Fish

Yet another minipost in my comparative anatomy series! But this one might be the strangest paring of all.

Rodents and fish – could there be any more different animals? And yet, I find that students just starting out in archaeology tend to confuse the two together. To be fair, it’s very understandable – the size of rodent bones can be comparable to the size of many fish bones. So let’s break it down and see how different they really are.

For starters, let’s look at the cranium of a rat (left) and an Atlantic cod (right). As you can see, most elements of the skeleton look completely different. The rat has the sort of skull you would expect to see with any animal, while the fish…well, fish are basically made of a head and a tail, so most fish bones you find will be part of the cranium. As I’ve mentioned before in my previous post on fish bone, they will also have a different sort of texture and look compared to mammal bone – in my opinion, its a very “fish-like” texture, a bit shiny and flaky. Always a good giveaway that you’re dealing with a fish!

So how is it possible to even confuse the two? Well, let’s look at something a bit trickier…here’s the vertebrae from a rat (left) and from a fish (right). Now, if you don’t know that there’s a difference in shape between rat and fish vertebrae, you might not be able to differentiate the two right away. And given how weird vertebrae can be in varying shapes between types of vertebrae in an individual body, who knows! Maybe they’re from the same animal?

Luckily, there is a visual difference between the two. Rat vertebrae look relatively similar to any other mammal vertebrae (“relatively” being the key word here, of course…but talking about the differences in mammal vertebrae is a post for a different day!). Fish, on the other hand, have very distinct-looking vertebrae and vertebral bodies. Unfortunately, distinguishing between the two can be more difficult if the vertebrae are more fragmented – I’ve seen many students get the two confused if most of the vertebral arches and “wings” are missing.

“But Alex!” I hear you say, “these bones look so different, I don’t believe that anyone could get them confused!” Okay then…let’s take two random, slightly fragmented bones from a herring and a mouse then, shall we?

As you can see, it can get tricky! Fragmentation, size, preservation of bone – these are variables that you encounter with archaeological bones that make things a bit more challenging than you’d think! The best way to get better, of course, is to practice, practice, practice. It gets easier…

…well, eventually.

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