Friday mystery object #460 answer

Last week I gave you a somewhat challenging bony mystery object to have a go at identifying:

The first challenge is recognising the type of bone. It’s not part of the axial skeleton (like the skull, vertebrae, ribs, etc) and it’s not one of the long bones, which are very distinctive.bits of the appendicular skeleton (which includes the pelvis, shoulders and limbs).

So that leaves the distal bits of the limbs, which tend to be relatively small. This is where it helps to be familiar with bone shapes – and this sort of elongated rectangle with an articulation at just one end is fairly distinctively a heel bone or calcaneus. (N.B. the end without the articulation provides a connection point for the Achilles’ tendon.)

At 8cm it’s fairly large, so that suggests it’s from a fairly large animal. This actually confused me more than it probably should have – but more about that in a minute.

The calcaneus is a very functionally important piece of bone, so the shape will reflect the use. However, the use of a leg tends to be broadly similar between closely related animals. Therefore, while it’s fairly straightforward to rule out things like carnivores and primates by using online reference resources like the incredible helpful BoneID site, it all gets more complicated when you realise this is from a member of the Artiodactyla, which has 270 or so species.

Common species are a good place to start with comparisons, since you are more likely to find their bones. So I started by looking at Deer, Horse, Pig, Sheep and Goat. I probably got a bit sidetracked by the size of this particular specimen at first, but as I have maintained on many occasions, size can be misleading and shape is always a better factor upon which to base an identification, since animals of the same species can come in different sizes.

After ruling out Deer, Horse and Pig I found myself wavering between Sheep and Goat. To dig into the shape differences a bit more, I took a look at an interesting paper on geometric morphometric comparison between the calcanea of Sheep and Goats by Lloveras, et al. 2022. The shape is very similar between the two species, but the differences identified in that paper have me leaniing towards the idea that this mystery object is most likely the calcaneus of a Sheep Ovis aries Linnaeus, 1758.

The differences are quite hard to decribe in a non-technical way, in the paper it goes like this:

According to our results the shape differences across sheep and goat calcanea are mostly located on the calcaneal tuber and neck, the sustentacular tali region, the malleolus articular surface and the cubonavicular articular surface. In general terms, in sheep, the calcaneal tuber tends to be more concave on the anterior side and the calcaneum neck, the sustentacular tali region and the cubonavicular articular surface tend to be wider. In opposition, in goats, the malleolus articular surface region tends to be shorter and more prominent anteriorly. These morphological differences could reflect the functional adaptation of these animals in different habitats that demand different methods of locomotion. While the sheep is adapted to running across flat land, the goat is adapted to rocky escarpments.
Lloveras, et al. 2022

In general terms it’s probably sufficient to take a look at the specimens on BoneID (you’ll need to flip the mystery object in your head, as it’s upside down and a mirror image since it’s from the right leg rather than the left, which is what’s shown on the BoneID site). The angles and extent of the articulations seem to be better defined in Sheep and match more closely to the mystery object.

So congratulations to Adam, who was the first to figure it out (beating me to it, which led to some rapid back-pedalling by me in the comments!)

Finally, back to the size. All I can say is that the sheep that this calcaneus came from was, well, quite possibly memeworthy…