What better way to kick off what will inevitably be a spottily updated blog than with a series of posts on my collection of various and beautiful things? Today’s subject is a slightly beat-up skull of a juvenile white-tailed deer, Odocoileus virginianus.
This skull is particularly interesting for a few reasons, apart from its obvious good looks. I’d wager that deer skulls, and the skulls of ungulates in general are pretty familiar, at least in general shape, to most laypeople, so anyone can see that the skull is far from complete. I do have the nasals, both of which were removed in order to fish out the sinuses which never really got clean despite lengthy baths in acetone and hydrogen peroxide that I subjected the skull to. Other than that, however, this is what I have.
Immediately noticeable are the missing premaxillae, and with them a good portion of the maxillae in front of the first premolar. The whole nasal area of the skull is broken up – not just the delicate structures in the maxillary sinuses, but the palatal portion of the right maxilla as well. The reason for this will become apparent later on.
Possibly related is the absence of the most of the animal’s basicranial anatomy. This gives a nice view into the braincase where we can see some unclosed sutures. Speaking of unclosed sutures, one of the lines of evidence that lead me to the diagnosis of this specimen as juvenile (let’s say I’m a bit slow and didn’t notice the sharp teeth, juvenile antler morphology, and small size) is the suture closure, subject of an interesting paper by Christopher Nicolay and Mark Vaders. Naturally I assumed that the sutures on a young animal would be far less complex than those on a full adult. It’s a character that’s easy to pick out would seem difficult to quantify, given that suture closure is a matter of squiggliness.
Luckily, squiggliness is in fact measurable, and the authors measured coronal and frontoparietal sutures in 67 specimens and analyzed their length ratio and fractal dimension. Their main takeaway was that there was surprisingly little suture variation between males and females, which is unexpected given the males’ antlers, which you would expect place additional mechanical load on the sutures. My main takeaway was in just how diverse fractal dimension and length ratio were between age groups. It appears that these measures of suture closure/suture complexity are fairly diverse after the deer hits about a year old. At half a year old, some specimens had more complex sutures than animals ten times their age, which tells me that surprisingly, suture closure might not be a helpful character for age diagnosis in this animal after all. Good thing there’s heaps of other information.
Observant or particularly patient readers will remember that, before this digression on cranial sutures, I hinted at the specimen having some atypical aspect. Even more observant readers will have already noticed what that aspect is.
Yes, this skull was ravaged by some canine, which left very clear bite marks on the maxilla – actually cracking the bone of the animal’s palate – and on the posterior of the skull, which can be seen in the picture of the cranial sutures (on a side note, I’m wondering why the parietal foramina in deer are aligned on the saggital axis rather than paired as they are in humans). The second set of bite marks was almost certainly long post-mortem, as I can’t imagine how a coyote or dog would have been able to bite a deer’s head off from behind at the neck.
It’s things like this that make collecting and studying specimens so rewarding. While it’s always a bit annoying to have an incomplete skull when a complete one has those beautifully withered-looking tympanic bullae, in the real world animals are imperfect and therefore their skeletons are imperfect as well, not just because of growth and life, but also because of death. I’m still on the lookout for a nice, complete deer skull, but this one, tragically young as he was, is a great example of a subadult and an excuse to do some armchair taphonomy.
Nicolay, Christopher W., and Mark J. Vaders. “Cranial Suture Complexity in White-tailed Deer (Odocoileus Virginianus).”Journal of Morphology J. Morphol.: 841-49. July 2006