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.

Rat and Fish Cranium

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!

Rat and Fish Vertebrae

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?

Mouse scapula and herring fragment
Can you tell the difference?

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.

 

On Animal Teeth, or Why I’m Not a Dentist

Since my last post using comparative anatomy was rather popular, I figured I should write a similar post for this week, starting with the most important part of the skeleton for zooarchaeologists (in my opinion) – teeth!

In my experience, teeth are the best skeletal elements to recover. Why? They’re one of the more easily identifiable parts of the skeleton and one of the more variable skeletal elements across different species.

Unfortunately for me, they’re also some of the…well, grossest parts of the skeleton. Nothing will put the fear of root canals and cavities in you like looking at any worn down tooth from a cow or sheep!

Here is a small sampling of teeth from different animals and how you can easily identify them, in very informal and non-technical-sounding ways:

Pig

Pig teeth might be the weirdest looking teeth I encounter regularly (besides my own…and if you’re my dentist reading this, no I will never get braces, I can’t afford them!). The easiest way to ID them is to recognise how similar they look to human teeth…but just slightly off. Basically, I like to say that the molars look like human teeth that have popped a bit like popcorn. Yes, I’m aware of how gross that is – but that’s how I remember them!

Pig Teeth
Yuck – here are the teeth of a domestic pig.

Dog

Dog teeth have a sort of “wave”-like shape to them that makes them a bit distinct. Often, I’ve found that their molars and premolars not as pointed and sharp as a cat’s teeth (see below), but that isn’t always the case, of course. In any case, dog teeth are quite bulky in comparison to cat teeth.

Dog Mandible
A detailed look at a dog mandible (Photo Credit: Melissa Rouge, Colorado State University)

Cat

Cat teeth have a somewhat similar shape to dog teeth, but I’ve found that they are somewhat more pointy than most dog teeth (although again, this may not always be the case). In comparison to dog teeth, cat teeth are also relatively smaller and not as bulky. A larger set of teeth that may look cat-like could indicate you’ve got another member of the Felidade family (i.e; lion, lynx).

Cat teeth
The dainty, pointy teeth of a domestic cat.

Sheep

The easiest way to ID sheep teeth is to check for a “house shingle”-like appearance. I have found that in comparison to animals with similar looking teeth (cows and horses), sheep teeth are also rather thinner. Be careful, though – sheep and deer teeth are remarkably similar in size and appearance!

Sheep Teeth
The maxilla and mandible of a sheep – note that house shingle look!

Cow

As mentioned above, cow teeth are similar in appearance to sheep with a slight “house shingle”-like appearance. However, given the difference in size, cow molars and premolars will be larger and bulkier, usually.

Cow teeth
Compare these cow teeth with the sheep teeth above

Rodents

And finally, some of the smallest teeth you’ll run into: rodents! To be frank, if you find very small teeth, it is most likely from a rodent of some kind. The front incisors may be a bit more difficult to ID if found alone as they are much larger than the other teeth and may be mistaken for a bit of rib bone. These teeth are what create the pattern of gnawing attributed to rodents that looks like long striations or lines on the bone (more on that in a future post!).

Rat teeth
The skull and mandible of a rat – look at that incisor!

If you’re looking for a more in depth comparison of mammal teeth, I would recommend Mammal Bones and Teeth by Simon Hillson (1992). It’s a great guide that I use in my work with some really clear diagrams.