Here’s that pig-skull multiview you ordered

November 27, 2019

Long-term readers will remember that way back in the pre-history of this blog, I wrote about my experience de-fleshing a pig head, which because the very first part in our ongoing series Things to Make and Do. In a subsequent post with a sheep-skull multiview, I included the multiview of that pig skull, too. Here it is:

Mike’s first pig skull, cranium only. Top row: dorsal view, anterior to right; middle row, from left to right: posterior, right lateral and anterior views; bottom row: ventral view, anterior to right.

As I noted in that sheep-skull post, I no longer own that skull: I donated it to be the first prize for the quiz in the very first TetZooCon, and it was won by Kelvin Britton.

But around the same time, our church hosted a barbecue even in which an entire pig was slow-roasted, and at the end of it I took the head home and prepped the skull out of it. The bone was much more fragile for having been roasted instead of simmered, and was in some danger of crumbling apart, but I stablised it with diluted PVA and it holds together OK.

Here it is:

Mike’s second pig skull, cranium and mandible in articulation. Top row: dorsal view, anterior to right; middle row, from left to right: posterior, left lateral (reversed) and anterior views; bottom row: ventral view, anterior to right.

Even allowing that the new skull was photographed with the mandible in place, the difference between the two is shocking. In particular, check out the dorsal views: the zygomatic arches of the first pig protrude way further laterally, and are much more robust than those of the second pig, and the whole shape of the skull roof is different.

I’m not sure what to make of this. I assume what we’re seeing here is variation of different breeds within the single domesticated species Sus domesticus, analogous to the way bulldog and greyhound skulls differer dramatically despite both being breeds of Canis familiaris. There are a lot of pig breeds out there, so perhaps it’s not too surprising. On the other hand, while the different dogs were bred for different purposes, I’d have thought all the pig were bred for the same purpose: to put on weight and provide meat. So I don’t know why such different skulls would have been selected for.

22 Responses to “Here’s that pig-skull multiview you ordered”

  1. Antonio Dias Says:

    Variability.?

    A breeding preference for more meat, let’s say, may be too vague to overcome the variation potential of breeds developed/evolved in different places. These variations will have developed in isolation and persisted since there was never any breeding pressure put on directly suppressing them.

    Given time and separation these breed differences could/might lead to future speciation.

    It does make a sobering impression when so much is made of even slighter variations when looking at fossilized evidence!

  2. Matt Wedel Says:

    Wow, you got that second skull astonishingly white! What did you do differently?

  3. Mike Taylor Says:

    @Antonio: yes, variability — but my intution(*) is that variation doesn’t become that extreme in the very short timescales we’re talking about unless there is artificial selective pressure, as with dogs. Pigs have been domesticated for, what, a few thousand years? For the root stock to have differentiated this much in that time strains credulity.

    (*) For what that’s worth, which is roughly nothing.

    @Matt I have no idea, sorry — that’s just how it came out. As far as I recall, I didn’t bleach it or anything.

  4. Antonio Dias Says:

    Throwing some more intuition* at the question, could it be that a combination of the transport and therefore spread of Sus domesticus around the globe over the course of a few thousand years coupled with the application of artificial selective pressure has created a situation somehow resembling the kind of natural pressures appearing in the geological record? Does this mechanism perhaps shine a light on the mechanics of genetic radiation? In other, fewer, words, when populations are dispersed and breeding pressures come into play variation proliferates?

    Isn’t this what we see after extinction events and convulsions in the past? What makes it happen so quickly in the cases of domestication is that in these cases short-term point-pressures have been applied by breeders as opposed to a slower and non-directed dynamic inherent in natural selection?

    “life finds a way…”

  5. Mike Taylor Says:

    That does sound reasonable.

    Does anyone know if there is anything remotely comparable across the various forms of domesticated cattle? Sheep? I assume all domestic cat skulls are pretty much the same … but maybe I shouldn’t?

  6. dale mcinnes Says:

    Perhaps the differences R not just the type of grains these pigs R reared on but, weather or not they R allowed to free range and dig 4 grubs rather than simply placed in a factory or a wallowing pen. Find out where these pigs R from and that may answer your quest.

  7. dale mcinnes Says:

    There’s a lot of variety among cats as well. I’m talking small breeds like jaguarundi, caracals (karakals) and servals. They all hunt the same but for some reason have this built in variation including colour and camouflage patterns.

  8. LeeB Says:

    Pigs were domesticated twice; once in the middle east and separately in China.
    Chinese breeds were more recently introduced to Europe because they put on weight faster and get bigger; your pigs could represent extremes of the two separate domestication events.
    With regard to domestic cat skulls; persian cats are very brachycephalic. Also cat breeds that evolved in south east Asia are quite gracile and often long nosed, whereas northern long hair breeds from Scandinavia and Russia are heavier with bulkier skulls.

    LeeB.

    .


  9. hm……..

    is this simply age, maybe?

  10. Mike Taylor Says:

    @Dale, I meant only domestic cats of the species Felis catus, so to be analogous with the variation in domestic dogs.

  11. Matt Wedel Says:

    Pigs were domesticated twice; once in the middle east and separately in China.

    At least, and it was probably a LOT more complicated than that. In a 2006 review paper, Albarella et al. had this to say (p. 219):

    “There are a number of extant wild Sus scrofa lineages from which recent domestic animals do derive, clearly indicating that pig domestication occurred independently in several diverse geographic locations across Eurasia. Thus, in the Far East, there appears to be a likely minimum of three (but possibly more) wild lineages that were domesticated (two in China and additional ones in Burma/Thailand and northern India). From Wallacea (samples from Halmahera and Papua New Guinea), there is possible evidence for the independent domestication of an introduced ancient lineage of pigs from elsewhere in Island or South East Asia not so far sampled [genetically] by us. But perhaps most exciting is clear evidence from Europe that points to the independent domestication of probably two wild lineages that form the basis for all modern European breeds (including those that were later improved by mixing with Asian types).”

    Unless that has been overturned by more recent work, as many as six or seven independent domestications of pigs might have taken place. That is flat-out amazing.

    Ref:

    Albarella, U., Dobney, K., and Rowley-Conwy, P. 2006. The domestication of the pig (Sus scrofa): new challenges and approaches; pp. 209-227 in Documenting Domestication: New Genetic and Archaeological Paradigms. University of California Press, Berkeley.

  12. Ben Says:

    UK pig breeds were certainly bred to take advantage of different environments and foodstuffs, so it’s maybe not a surprise that they might have different skulls. Gloucester Old Spots are known as orchard pigs, Tamworths are reputed to do well in woodland, and the Middle White roots (eg digs) less than other breeds. There’s an obvious difference in skull shapes between the Tamworths and Middle Whites that I’d assume reflects their different habits – Tamworths apparently love digging.

    If they’re being bred for certain habits and behaviour (Tamworths have a reputation for being less domesticated, and may get territorial) would you expect neotony to start showing up as one part of the genetic toolkit?

  13. LeeB. Says:

    Another thing that seems to have happened in Europe is that domesticated pigs were brought in from the middle east but then these bred with the local european wild pigs and over time the genetics of the domestic pigs came to represent European bloodlines; perhaps the European pigs did better in the colder climates and were selected for by the farmers so over time the genetic signatures of the middle eastern pigs were lost.
    Basically the pigs were free range so crossing with local wild boars was ubiquitous.
    Thus the idea of domesticating pigs spread and even if domestic pigs were moved about sometimes it would be difficult to tell an independent domestication of local wild stock from an introduction of a limited number of domesticated pigs from elsewhere and then continued crossing with local wild pigs for millennia.
    Incidentally the Sulawesi wild pig is supposed to have been domesticated and then spread to the Moluccas and New Guinea; it was then hybridised extensively with pigs of Sus scrofa origin.

    LeeB.

  14. LeeB. Says:

    Also cats were domesticated (at least) twice; once in the middle east and once in Egypt; the Egyptian bloodlines then spread and tended to displace the middle eastern bloodlines.

  15. Matt Wedel Says:

    even if domestic pigs were moved about sometimes it would be difficult to tell an independent domestication of local wild stock from an introduction of a limited number of domesticated pigs from elsewhere and then continued crossing with local wild pigs for millennia.

    I’ve read about that, and it’s mind-blowing, but it makes sense. Like the introduced domestic pigs were a sort of domestication seed, that worked so well that the genetic trace of the founders was all but lost in time.

  16. Mike Taylor Says:

    Homeopathic domestication.

  17. Matt Wedel Says:

    Belatedly: thanks, Ben, for the info on the habits of the different breeds. I didn’t know any of that. You also asked:

    If they’re being bred for certain habits and behaviour (Tamworths have a reputation for being less domesticated, and may get territorial) would you expect neotony to start showing up as one part of the genetic toolkit?

    Maaaaybe. Neoteny or paedomorphosis has been proposed for a lot of domesticated animals, including pigs, but Evin et al. (2017) found that domestic pigs were not markedly paedomorphic, other than just having short snouts compared to their braincases. But the shapes of the snouts and braincases are quite different from their wild ancestors, so why some domestic pigs have straight snouts (like Mike’s second skull) and others have “foreheads”, like Mike’s first skull, is as far as I know still an open question.

    Ref:
    Evin A, Owen J, Larson G, Debiais-Thibaud M, Cucchi T, Vidarsdottir US, Dobney K. 2017. A test for paedomorphism in domestic pig cranial morphology. Biology Letters 13:20170321.
    http://dx.doi.org/10.1098/rsbl.2017.0321

  18. Mike Taylor Says:

    At TetZooCon, one of the speakers — I think it was Rebecca Lakin — made the well-received point that sexual selection is to palaeontology what religion is to anthropology: the explanation everyone falls back on for something they can’t otherwise explain. I rather fear paedomorphosis might be another of these get-out-of-jail cards.

  19. LeeB. Says:

    One set of genes that might have been strongly selected for and might have been retained when populations of domesticated animals were moved about are those that control docility or tractability, you want domestic animals that allow you to handle them and their offspring without trying to kill you.
    Even so taking piglets away from a barely domesticated sow or milking a cow that wasn’t far removed from being an aurochs must have been a job for the brave. Effectively you may have ended up introgressing genes for docility and other selected for traits into the local population of wild pigs (or cattle), specifically the sub-population that was kept under human control.

    LeeB.

  20. william dale McInnes Says:

    In paedomorphism, just take a quick look at the ceratosaurs and their offshoot …. the abelisaurs.

  21. Brad Lichtenstein Says:

    Without really passing judgement on sleek vs robust, in my brother’s farm model (based on Joel Salatin’s farm business), the pig’s role is for aiding composting. They root around the muck at the bottom of their barn, and they also often directly convert human food waste to manure. Now, Salatin only uses somewhere fewer than a handful of pigs on his farm, he’s primarily a way-beyond-organic beef producer who has cleverly used other animals in place of machinery, to accomplish farm tasks, which yields extra profits in place of extra expenses. Factory pig farmers would probably focus more on weight.


  22. […] this post before the very interesting discussion of pig domestication flared up in the comments on Mike’s pig skull post. Mike’s two skulls nicely illustrate the difference between forehead-less and, er, […]


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