Skulls will tell you a lot if you will take the time to look and learn.
For example, these two skulls are from my collection and both are bulldogs.
One is an English Bulldog, and the other a large American Pit Bull.
Look at these two skulls carefully and pay special attention to the area where the brain would sit (I will measure true cranial volume in another post).
Look at the smooth dome on top of the English Bulldog as compared the occipital and saggital crest that comes with the American Pit Bull.
What's that mean?
What does it tell you about the relationship between brain size and jaw strength?
I am adding another skull for comparison -- two pictures of the same skull, below. This is an average-sized red fox skull. Notice the relative size of the brain case and the lack of a saggital crest. What does this tell us about the brain to jaw-strength ratio?
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8 comments:
I am not sure exactly what you are getting at here. What strikes me most is how deformed the skull of the British Bulldog is. Yes, the Pit Bull skull has modifications to allow the muscle attachments that make the jaws powerful, but the brain case is the same relative size and shape as a German shepherd or poodle or border collie all of which I would consider to be intelligent. Whereas most breeds with domed skulls like the bulldog are not acknowledged for their intelligence.
In order to come close to understanding, I had to look at a Doberman's skull- whose claimed bite is 600lbs but I can't find the relation in brain size and bite as I do the zygomatic arch and the mandible. You totally have my attention here! Please elaborate!
Large saggital crests means large jaw muscles. The crest is where the muscles for the jaw attach, so the more muscle mass you have the more bone you need to attach those muscles to. Take a look at the saggital crests on a Gorilla (insanely huge).
First time posting here. The thing that most strikes me about the English bulldog skull (after staring at the enormous diastema left by the misaligned jaws) is how globular the skull is. It's nearly human-like in that aspect. On the subject of jaw strength, it reminds me of the unusually weak jaw muscles humans have compared to other great apes -- they have much bigger attachment sites for their jaw muscles. Better muscling overall, actually, but I deviate.
Can't comment on brain capacity, but I'd say that the vaunted 'bulldog' grip is more fantasy than fact.
Dei.
still not a zoologist, but still thinking... Bite strength seems to be composed of three things: first, the strength of the muscles that close the jaw; second, the quality of the teeth, how sharp, how thick the enamel, their shape and how they meet; third, the shape of the jaws themselves.
Muscles aren't everything -- many herbivores have very strong jaw muscles and many carnivores have surprisingly weak ones, but relative to the archetypical pariah dog, bulldogs have compromised attachment sites to support muscle, which will adversely affect bite strength.
Teeth. One hallmark of Carnivora are the shearing carnassial teeth and sharp pointy teeth. Carnivores that consume bones as well as flesh tend to have thicker enamel on their molars and premolars compared to those that don't. Again, bulldogs don't fare well. Their teeth are not on speaking terms with one another, with the valuable lower canines way out in front of the upper ones, rather than interlocking as most dogs' do. The carnassials and molar teeth are crowded at the back and there's a great big gap in the dentition. Dogs can live off bones with a bit of meat on them (provided they're not adult cow shin bones). A bulldog with the pictured dentition would struggle.
What about jaw shape? Cats have stronger bites relative to dogs and that has as much to do with their short jaws as it does with their wickedly sharp teeth. In light of this, the tendency among molosser-type dogs is to have shorter jaws for just that reason, but in bulldogs, that falls off the cliff into pointlessness -- the misaligned jaws make biting harder, not easier.
Nope, this isn't the skull of a dog that can hang off the nose of a bull -- not that one wants a dog to.
The Pit Bull skull resembles the 19th Century Bull dog skull. The Bull dog skull looks like it would hold a bigger brain, but as pointed out looks like it completely lacks a saggital crest for muscle attachment and therefore lower jaw strength.
When humans evolved (naturally) from apes they lost the saggital crest and jaw strength but gained bigger brains and more intelligence. They used other methods to fight and hunt making tools?
The Pit Bull skull also looks broader than the bull dogs.
I read a paper recently that looked into jaw strength relative to skull shape. It said that a large brachycephalic dog has more bite force compared to a large doliocephalic dog. However, a small brachy didn't have a stronger bite force than a small dolio or mesaticephalic.
The significance was that the small brachys the brain case was disproportionately large having lost facial bones for the attachment of the masseter muscles. Paedomorphism.
The fox is interesting as it resembles a mesaticephalic dog. It looks like it has a small brain case but plenty of room for the masseter muscles.
Now looking back at the bull dog picture it looks scarily like a human crossed with a Pit Bull!
Looking forward to your conclusions.
The general point was made in the comments: the muscles that attach to the jaw have to be anchored somewhere, and they are anchored at the cranium. In animals with relatively strong bites and small brains, a sagittal or occipital ridge of bone is created to increase the surface area for muscle attachment as you see with the Pit Bull.
In the English Bulldog, you have a dog that is entirely human made. This dog cannot breed naturally, cannot whelp naturally, and often cannot even eat from a bowl due to the massive undershot of the jaw.
Along with the brachycephalic face created by shortening the muscle, breeders have bred for a massive dome skull which makes for a convenient place to attach the muscles for the jaw which are, in fact, much weaker and much less used that those of the Pit Bull.
The top and botton jaw of the English Bulldog only have a nodding relationship with each other, which means the English Bulldog can not only not grip very well, they generally have bad teeth to boot, as the teeth cannot grind on each other for self-cleaning.
Brain size and "intelligence" as humans typically define it do not have that much to do with each other for the simple reason that humans see animals through a lens we grind outselves. We deem an animal "intelligent" if it is biddable to our commands and attentive to our needs, confusing intelligence with obsequiousness.
A more interesting issue is brain shape -- a topic for another post. Shape actually **does** tell you things!
Size factors in here too. The various species of fox are the smallest natural canids, and the smallest of foxes (about 3 or 4 pounds for desert foxes) are about as small as a canid brain can go and remain well designed. Smaller than that, and the brain case does not close, and you have an open brain case, as you with the Chihuahua's "molera".
With the red fox skull (this one was 14-pounds), you have a relatively large brain for the size of the animal, and that large brains results in a wide and smooth skull cap which is area enough to attach the jaw muscles. Those jaw muscles, sharp teeth and jaw bone are all strong enough to sever a human finger, but not big enough to crack a deer leg bone. Fox, we must remember, mostly live on mice.
Much has been made of the fact that a wider head makes for a stronger bite, while missing the most important point: a stronger bite is generally not needed. With the exception of the Hyena (which is neither dog nor cat) which cracks bone and grinds it to dust, and which eats a lot of marrow as a consequence, most carnivores are over-equipped in terms of bite pressure, and so the face remains a bit longer in those animals that use scent to find game -- such as wolves and dogs.
In addition, a longer muzzle helps cool off a dog that is heated from a chase.
Remember that it hardly matters how strong your bite is if you can find nothing to bite on (no scent abilities), and if you get over-heated and winded while chasing game due to a shortened and smashed muzzle -- which is why English Bulldogs are a complete mockery as a working dog, but Pit Bulls are not.
I agree with PBurns.
I personally own a Pitt bull terrier named Tico, not a mean bone, nor stupid cell in his body. He has out lived five dogs, simply because he was smarter. Waited for the cars to go by. Didn't chase the chickens.
And I must also add that the size of the brain really doesn't matter when it comes down to it, it's about density and weight.
Compare Einstein's brain to yours. And you'll see that the former's brain is relatively smaller, and the later is surprisingly less dense, meaning that it's more likely to get things crammed in there that would otherwise have been evicted in the former's mind in favor of how to brush his own hair after his first wife left him.
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