How the Shape of a Dog's Head Affects Behavior and More

The Canine Skull

Even a casual observer must be struck by the diversity of sizes and shapes represented by humans’ best friend, Canis familiaris (the domestic dog). Just consider, the smallest chihuahua and the biggest Great Dane both belong to the same species! That kind of breed-to-breed variability also applies to the shape of the canine skull, as measured by the cephalic index, (also known as the cranial index) which is the ratio of the skull’s breadth (or width) relative to its length.

There are three basic categories:

A Boston Terrier (a brachycephalic breed) with a Shorter Nose and Flat Face

Brachycephalic breeds are the shorter-nosed, flat-faced dogs with the highest cephalic index meaning their skulls are about as wide as they are long. Breeds include:

• Pugs.

• Boston Terriers.

• Boxers.

• Bulldogs; and

• Pekingese.

Greyhounds (a dolichocephalic dog breed) have long skulls and noses

• Dolichocephalic breeds are those with extremely long skulls and long, slender noses (or low cephalic index). Breeds include:

  • Greyhounds.

  • Setters.

  • Dachshunds.

  • Italian Greyhounds; and

  • Great Danes.

• Mesocephalic dog breeds exhibit skulls of intermediate length and width. Breeds include:

  • Beagles.

  • Golden Retrievers.

  • Labrador Retrievers.

  • German Shepherds; and

  • Pomeranians.

So what are the drivers and consequences of different cranial dimensions among canines? The answers to those questions tell us a lot, not only about the dog’s abilities, but also about what humans value in their K9 companions.

Shape of A Dog’s Head: Vision

Dogs with high cephalic index tend to have a centralized cluster of retinal cells (which send visual stimuli to the brain). As a result, Pugs and Bulldogs have great visual acuity in the center of their visual fields, but less in the periphery. This arrangement enables them to detect movement directly in front of them and may therefore enable them to follow a human pointing gesture. Dogs with this visual set-up make good guard dogs and fighters. Their compact and powerful jaws also endow them with greater bite force than that seen in longer-skulled species.

In contrast, breeds that have hunting responsibilities tend to be dolichocephalic - they have relatively elongated skulls and long noses. Their visual morphology enables them to see objects on the horizon and detect motion at the periphery, useful qualities for sighthounds.

Shape of a Dog’s Head: Sense of Smell

Does having a short skull and a short nose affect how well brachycephalic dogs detect the aromas around them? Do their long-nosed brethren do a better job at sniffing out smells? It would appear the answer to both questions is “yes!” The olfactory areas of a flat-faced dog’s brain are shaped differently from those of other dogs and are also somewhat displaced in their brains. The compression of the cranium also leads to a reduction in the brain matter devoted to smelling. Consequently, they tend to perform more poorly on odor discrimination tasks than other dogs.

Shape of a Dog’s Head: Appearance

A Cavalier King Charles Spaniel

The current popularity of French Bulldogs, a paradigm of brachycephalic appearance, indicates how human breeding efforts can dictate the shapes of dogs’ heads. Short-nosed dogs are prized for their cute, baby-like features. Dog breeders have pushed canine skull shape to its pathological limits, creating negative health compromises for dogs bred largely for their facial appearance. Still, if you want an adorable companion dog, consider a Cavalier King Charles Spaniel. Just be aware of what you - and the dog - have sacrificed for appearance.

Woman Training a Dog with a Medium Length Nose (a mesocephalic breed)

Shape of a Dog’s Head: Trainability

The physical capabilities that accompany a dog’s head dimensions seem pretty obvious. But can a dog’s ability to learn also be associated with canine cranial measurements? Hypothetically, it might be that dogs with cranial shapes reflecting highly specialized roles - guarding and fighting for short-nosed dogs and hunting and chasing for long-nosed pooches - are less trainable than animals with a more generalized morphology (dogs with medium-length skulls and snouts).

Results from several studies on this topic suggest that the low-trainability groups of dogs tend to be more brachycephalic than the trainable groups. Overall, the breeds perceived as most readily trainable were more consistently mesocephalic (with moderate-length snouts). Collies, Labs and German Shepherds all fall into this group, the flexible and compliant pooches that can learn to perform a variety of jobs.

Brain Plasticity

Despite the apparent relationships among cranial shape, brain neuroanatomy and capabilities, the connections may not be simple. We’re learning that the human brain is plastic; i.e., that it has the ability to change and even change shape, over the course of an individual’s life. Research has shown that, if a portion of the brain is compromised, the cognitive operations that resided there may shift to another brain area.

Might brachycephalic breeds benefits from this phenomenon, such that the loss of brain territory in one area (say, for smelling) might be relocated to another? This seems plausible.

But, at the same time, all of this should remind us to be cautious as we attempt to draw connections among skull dimensions, breed characteristics, canine capabilities and behavior.