On Friday I asked you to spot the differences between these two cat skulls and I wondered whether anyone could identify them:

Both henstridgesj and Allen Hazen made some good observations, the first being about the difference in size, then about morphological features that I’ve marked on this image:

Now henstridgesj also correctly identified one of the skulls – the one on the right of the image is from a Domestic Cat Felis catus Linnaeus, 1758.

As it turns out, this was a bit of a trick mystery object, since BOTH of the skulls belong to Domestic Cats, so this gives us a useful idea of the kind of variation we might expect within a species.

I think that the main cause of variation between these two animals is probably sex, with the male on the left and the female on the right. There may also be differences based on age (although I don’t think that’s a major factor), breed and perhaps disease (the larger specimen looks like it had an infection that affected the surface of the bone).

After taking various measurements, the most useful difference I’ve found between the two skulls is shown with the yellow line. I think that the ratio of these two measurements may provide a way to tell the difference between a male and female cat (in the male it’s around 1 or less than 1, in the female it’s greater than 1) but I’ll need to make a LOT more measurements to test this.

Two other ideas that could be tested were suggested by henstridgesj and Allen Hazen. Allen said: “My impression is that the presence and development of sagital crests, among felidae, correlates pretty strictly with size” and henstridges said: “It seems that if the species of cats are arranged in increasing size order, then the anterior half of the skull (forward of the frontal-parietal suture) seems to increase in size more than the posterior half”.

I’d better take a look to see if this has been tested before…