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A first look at a very unusual skeleton


Often mammal skeletons look very similar. They have the skull, a spine made out of vertebrae, arms and front legs that come from shoulder blades, and back legs that are attached to hips. If you've seen a rabbit's pelvis you can probably identify a giraffe pelvis. If you have seen a hippo shoulder-blade you could probably identify a mouse shoulder-blade. But some mammals have adapted to where they live to the point their bones are difficult to identify if don't know about the species. That makes it both cool but also difficult when you look at their skeletons.

In May last year, a man called Ric Morris who reads my blog dropped by my house to drop off some cool stuff that he had found while beachcombing on holiday. There were loads of cool bones, but one of the most unusual was this thing in the next photo:

It was wrapped in not one, not two but three thick plastic bags, all cable-tied at the top. The reason was that inside was the body of a mummified baby harbour seal (also called a common seal). Dead animals don't smell that great, which is why it was wrapped in the bags.

After Mr Morris left, I spent about a month thinking about what to do with it. Sometimes I wished he'd brought a box of chocolates instead ! Normally I would leave it in a wood above ground, but seals are so smelly, and it would really confuse any gamekeeper who found it. Anyway I asked about and Ben Garrod of Ben's Bones came up with a good plan for removing the bones which is so secret I can't tell you what it is.

The first step was to rehydrate the tissue, since dried or mummified tissue doesn't decompose well. I took off the outer two bags, and stuck a hosepipe in the gap then filled the bag full of water and left it overnight. 

You might wonder what a half-decomposed mummified seal looked like after the flesh was rehydrated. I can tell you it looked pretty disgusting and smelt so too. I do not recommend you look at these pictures, but they are here if you really want to. This one is looking down into the bag, where the seal's head is at the bottom, and the back flipper is visible:
Very gross image. Click and hold down to see the full picture or click here to see in a new window.

This is the flesh at the bottom of the bag. I have no idea what part of the animal this is, not a clue:
Very gross image. Click and hold down to see the full picture or click here to see in a new window.

Anyway, the decomposition took nine months from start to finish. Afterwards, I cleaned the bones in batches, first in my S6 cleaner, then after that broke for a second time, in a slow cooker overnight, simmering in biological washing powder, changing the water two or three times, then drying in the sun.

I forgot to mention the other complication. Because the seal was young, the skull wasn't properly fused, and the ends of the longer bones were loose. Leg bones and other bones have growth plates, where new bone is produced, near each end of a bone. So leg bones (and other bones) of young animals have loose "caps" (scientists call these epiphysises). So a humerus (upper arm bone) which in an adult is just one bone could be as many as four or five bones in a young one. An adult vertebrae is in three or four parts in a child. A skull, which is fused in an adult, might be nine or ten parts in a child.

Any skeleton is a jigsaw puzzle but in a juvenile skeleton it's a jigsaw puzzle with maybe four times as many pieces. That's bad enough if it was an animal I am familiar with, like a deer, sheep or fox. But seals are more complicated still:

Seals may look more like fish, but they are from the same group of animals (mammals) as deer, sheep and mice. They breath air and have four limbs and hands and feet (which look quite human). But seals live in the sea, not on land. They need to cope with cold through layers of fat, not layers of hair. And their body weight is supported by the water or land, not by their arms and legs. That makes seal bones look completely different to the same bones in a deer or fox.

I had stored the bones in a box and this case:

And the first time I laid it out I found it very difficult:

The skull was in about nine or ten pieces, and the more it was cleaned the more it fell apart. This bit is the back of the braincase (with the spine hole) and the right ear bone:

With the help of an elastic band I could put a few more bones together (this is it upside down with both earbones):

This is the roof of the mouth with one canine still in:

There was only one lower jaw, the other one had been lost before the body was recovered:

The atlas (in the middle, the top neck bone) was easy to recognise, as was the axis (the second neck bone, on the left):

The scapula (shoulder blade) couldn't be anything else, I wrote about one before in my guide to scapulas. The hook points towards the back, so this is the right scapula:

The lower leg bones are more difficult to spot. The humerus (in the middle, upper arm bone) is short for the size of the animal and thick. In other mammals, the radius (top right) and ulna (bottom right) are long and thin and look quite fragile. Here they are short and fat and the radius is very thick at the wrist end (it's the wrong way round in this photo).

Seals have front arms like this because they need strong arms but which don't need to go very far from the body.

The back legs are just as odd:

This shows the pelvis, the femur, and the tibia and fibula (with the end loose on the tibia). The femur, which in humans goes from hip to knee, is very very short and very thick. In some animals the fibula is so thin it almost disappears, but not here, it's about half the thickness of the tibia. The fibia and the radius both help control the wrist or ankle movements which are important for swimming mammals.

The hips don't seem to join to each other , and the point they join on the spine seems quite small compared to other animals, but this joint never had to take the weight of the seal:

This is one of the unfused vertebrae, where it was in two parts (plus the epiphyses, making four bits in total):

Some of the vertebrae were quite thin, like in the neck:

When I work on the skeleton, a big help is going to be this 100-year old skeleton at the Huntarian Museum of Zoology which I was at a week ago. Dad took lots of photos to help with my skeleton:

This is the front right leg:

This is the front right flipper, which is quite like a human hand:

The back of the seal is very complicated:

The tarsal (ankle bones) are very very complicated here:

This was a brilliant present, and I hope to do more work on it and possibly even rearticulate it ! Thanks Ric Morris !

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ethan said...

Another great post, thanks. You have more patient than I do. I avoid juvenile skulls just because they take so much time putting back

Jake said...

I think seal skulls are particularly bad because of where the skull is narrow around the orbits, and it often breaks there.

Sea Wolf said...

You've done good with this Jake. Seal, whale and dolphin bones are very oily. One way that I clean them is to keep them buried in a layer of rotting horse manure. It takes time, about a year for whale type bones, but the bacteria in the manure gets rid of the oil and the rest of the oil in the bones is absorbed by the manure as well as all the stinky bits also rotting away. The bones will come out pretty clean after this treatment. Though, with something as small as what you have there, many bones would have been lost.

Jake said...

Thanks for the tip !

Rob said...

So, how many bones does a seal have?

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