Canine Noggins: Skull Morphology

By Emily Kubick

After thousands and thousands of years of evolution, domestication, and selective breeding, we are left with a plethora of dog breeds in all different shapes and sizes. The main component in the study of the evolution of the domestic dog has been skull morphology. (briefly discussed in my previous post Origin of the Domesticated Dog Over time, skulls have shrunk, grown longer, shortened, widened, and changed in all different ways.

Brachyceph-what??
Before I delve into the abyss of canine skulls and snouts, it’s important to understand the difference in skull shape and how they are classified.

In 1840, Anders Retzius first used the descriptive terms “dolichocephalae” and “brachycephalae” to aid in classifying human skull morphology. Today these terms are still used, with the addition of a third, mesocephalic. The following is a description of each classification term as it relates to dogs:

Dolichocephalic refers to dogs with long snouts, such as the Afghan Hound, Dachshund, Doberman, and German Shepherd.

Brachycephalic (brakēsəˈfalik) refers to dogs with short wide snouts with forward facing eyes, such as the Boxer, Chow Chow, Cavalier King Charles, and French bulldog.

Mesocephalic refers to all those snouts in between, such as the Australian Shepherd, Bernese, Mountain Dog, Cattle Dog, and Belgian Malinois.

Source: SC Psychological Enterprises Ltd.

In order to properly classify a skull, all you have to do is calculated the Cephalic Index. Easy as pie. Multiple the skull’s maximum width by 100 and divide by the maximum length. The smaller the value, typically below 75, the longer the head. The larger the value, typically about 75, the shorter the head. Of course, it is actually not that simple, and a little more scientific when you add in all the other factors of the shape of the skull, but the Cephalic Index is the first step.

Now that we know the different classifications of different breed’s noggins, how do these physical traits affect the dogs?

According to researchers: head shape, weight, height, and sex (basically most general physical traits) could have affected a dog’s natural behaviors and abilities. But I am obviously focused on how a dog’s skull can affect its livelihood.

Yay Retinal Ganglion Cells!
Besides physical skull shape, what behavioral abilities differ between dolichocephalic (däləkōsəˈfalik) and brachycephalic breeds? Vision is one difference.

So how do dolichocephalic and brachycephalic breeds differ when it comes to vision? Great question! One main difference lies in the distribution of their retinal ganglion cells!

Scientifically, retinal ganglion cells are found in the neurons near the retina’s inner surface and “receive visual information from photoreceptors through bipolar cells and retina.”

In layman’s terms, they are sensors that aid in what/how a dog sees and focuses on.

According to researchers, in dolichocephalic breeds have these cells are spread out, allowing for greater peripheral vision. With great peripheral vision, comes great responsibility. (Only kind of kidding). Great peripheral vision allows dogs to notice prey more easily, leading to a higher prey drive, creating excellent hunting dogs.

These cells are more centralized in brachycephalic breeds (commonly with forward facing eyes) according to researcher McGreevy. Research in other species has shown a correlation between these centralized cells and greater visual clarity, leading to the theory that brachycephalic breeds are able to focus their vision forward without the distractions from the peripheral. While these traits do not make good hunting dogs, they do give them the advantage of appearing soulful and connected. One study found that people tend to be more attracted and feel more connected with brachycephalic dogs, which lead to their selective breeding and the short snout becoming a “breed standard” for many breeds. And in this day and age, the ‘cuteness factor’ is almost as important as working abilities.

Simplified:
Dolichocephalic breeds excel in hunting due to their great peripheral vision.
Brachycephalic breeds excel in focusing and “connecting” due to their forward facing eyes and visual clarity.

Learn Your Dog
It is fun and important to keep learning about your dog no matter the breed. And It is imperative to keep learning about how to give the proper care and attention to your dog’s individual needs. Unfortunately, extreme brachycephalic breeds are susceptible to multiple health problems. With inbreeding and what many believe to be unhealthy “breed standards,” many squishy faced dogs suffer from respiratory issues, eye problems, and skin infections. So keep those squishy wrinkles clean and always be conscious of any health concerns. Your vet is your best friend!… I mean, not your BEST best friend, but they’re cool.

No One Knows it All
You may have noticed a reoccurring theme in many of my posts: There is still so much to learn! The history of dog domestication and canine science is filled with amazing facts and research but also riddled with plot holes and mysteries. It is extremely important to keep in mind that the research I shared above is only one part of a whole Doggiehood puzzle. It is not black and white. Just because a dog has a short snout, does not mean they can’t still have a high prey drive (Ever try to wave a toy in front of a Frenchie, you know what I’m talking about).

Can’t wait to keep on learning more pieces of the puzzle with you all! More to come soon!

Sources
Marchant, Thomas W. et al. “Canine Brachycephaly Is Associated with a Retrotransposon-Mediated Missplicing of SMOC2.” Current Biology, Volume 27, Issue 11, 1573-1584.e6
Holloway, Sarah. “Long Face Dog – Fascinating Facts About Dolichocephalic Dog Breeds.” The Happy Puppy Site, 22 Aug. 2017, thehappypuppysite.com/long-face-dog/. Accessed 24 Aug. 2017.

Coren, Stanley. “A Dog’s Size and Head Shape Predicts Its Behavior.” Psychology Today, Sussex Publishers, 31 Mar. 2016, www.psychologytoday.com/blog/canine-corner/201603/dogs-size-and-head-shape-predicts-its-behavior. Accessed 24 Aug. 2017.

Stone, Holly R., et al. “Associations between Domestic-Dog Morphology and Behaviour Scores in the Dog Mentality Assessment.” PLoS ONE, Public Library of Science, journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0149403. Accessed 24 Aug. 2017.

Franco, Fernanda Catharino Menezes, et al. “Brachycephalic, dolichocephalic, and mesocephalic: is it appropriate to describe the face using skull patterns?” Dental Press Journal of Orthodontics, Dental Press, www.scielo.br/scielo.php?pid=S2176-94512013000300025&script=sci_arttext&tlng=es. Accessed 24 Aug. 2017.

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