Friday mystery object #144 answer

On Friday I gave you another genuine mystery object from the Horniman’s collections:

It was in a box of unidentified and unlabelled bones which I’m pretty sure came from the King’s College teaching collection in the 1980s, when King’s merged with Chelsea College. Quite a large amount of material came to the Museum and unfortunately much of it was jumbled up, missing labels and quite often different parts from the same specimen had become separated.

I have been kept busy trying to make sense of it all, which is no small task, as the collection was mainly used for comparative anatomy meaning it is very diverse. The specimens in the collection could be from anything and from anywhere in the world – which makes it rather difficult to narrow down the options.

This specimen was a bit of a puzzle, since although it is clearly from a fairly large animal, it is quite hard to work out what the full adult size would be, as this bone is from a juvenile (as spotted by Kevin). This is apparent from the unfused ends of the bone (called the epiphyses).

One possibility that occurred to me (and Rhea) was that it may be the bone of an aquatic mammal, such as a seal. However, in aquatic mammals the humeri need to rotate, meaning that they tend to be flattened in two different planes at the proximal and distal ends. This bone is just flattened in one plane, meaning it wouldn’t be great for use in swimming efficiently and it wouldn’t be great for bearing large amounts of weight/force during locomotion – a more rounded cross-section of bone is better for that.

In fact, the general shape of the bone is wide and flat with large tuberosities for muscle attachment – almost like the humerus of a mole:

This is something that  Richard Forrest seems to have picked up on when he suggested that it is the humerus of a fossorial [digging] animal. This narrows down the options quite nicely, as there are only a few large fossorial animals.

The Pangolin was suggested by Dave Godfrey, but the bone is too large. Dave also suggested the Aardvark, which is a good contender, although not quite right. I personally have a different animal in mind – the Giant Anteater Myrmecophaga tridactyla Linnaeus, 1758.

Unfortunately I don’t have another Giant Anteater humerus for comparison, although there is this one from an adult Giant Anteater on the SUNY Orange comparative anatomy page on the arm. Despite some differences due to the age of the specimen, I’m happy that they are a good match.

One of the other reasons I think that the Giant Anteater is the correct identification is the fact that I had come across a radius of a Giant Anteater from the Kings College collection a while back and it was from an individual showing pretty much exactly the same degree of fusion of the bone, suggesting an animal of the same age.

In fact, that specimen was a mystery object from a couple of months ago, so my regulars will probably have seen it before! I do apologise for having the same species (indeed the same individual) used for two mystery objects, but I posted this one before I realised what it was. My next step is to see how well they fit together and then to look for the ulna, which may be in another box…

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