Why Some Mammals Have Longer Faces

In the realm of timeless puns, the classic “why the long face?” joke has intrigued humorists for generations, provoking a myriad of creative responses. However, behind the laughter lies a genuinely intriguing question that delves into the evolution of mammals, particularly those with elongated faces.

In our latest examination, we bring a scientific perspective to this age-old query, shedding light on a phenomenon known as “craniofacial evolutionary allometry” (CREA). Far from a random occurrence, CREA reveals a correlation between face length and body size in various mammalian groups, including cats, rodents, deer, kangaroos, and certain primates.

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Sheep and cows belong to the Bovidae family, yet cows, being larger, typically exhibit longer faces. A similar trend is evident in the comparison between the smallest and largest deer species. (Image credits: Sheep – Flickr/Tambako The Jaguar, Cow – PickPik, Pudu – Flickr/Robert Lowe, Moose – Flickr/Tambako)

Contrary to the belief that face elongation is an automatic byproduct of overall growth, we propose that the prevalence of CREA stems from the biomechanics of feeding habits. Animals within the same family often share similar diets, and the structure of their faces adapts accordingly.

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Creatures deviating from the CREA pattern typically adopt markedly distinct diets. For example, orcas specialize in capturing large prey instead of small fish, while the Tasmanian devil excels at cracking bones. (Image credits: Fennec fox – Rawpixel, Tibetan fox – Craig Brelsford, Quokka – Flickr/Jack Barsby, Kangaroo – Rawpixel, Dolphin – Tomaree Museum, Orca – Pexels Pixabay, Antechinus – Wikipedia/Mel Williams, Tasmanian devil – Pexels/Chen Te)

For instance, consider the parallel diets of sheep and cows, both herbivores consuming grass. Despite this shared diet, the smaller sheep need shorter faces for efficient biting due to increased jaw pressure. Analogous to the grip strength of barbecue tongs, shorter faces enhance biting force.

Conversely, larger mammals can “afford” longer faces due to their naturally powerful jaw muscles, requiring less effort in the biting process. This adaptability provides advantages across different situations – longer faces facilitate reaching more leaves for herbivores and accommodate larger fangs for carnivores.

While our proposed explanation aligns with the general CREA pattern, it also addresses outliers – species that defy the norm due to drastic changes in diet. Take the dog family, encompassing both small-prey hunters like foxes and large-prey hunters like wolves. Larger individuals within a group of foxes adhere to CREA, yet wolves, despite being larger than foxes, possess shorter faces, a reflection of their need for a stronger bite in hunting larger prey.

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Within the Canidae family, which includes the dog family, large-prey hunters requiring a more powerful bite typically possess shorter and sturdier faces compared to their small-prey hunting counterparts. (Image credits: Fennec fox – Rawpixel, Tibetan fox – Craig Brelsford, Bush dog – Flickr/Tambako, Wolf – PickPik)

Exceptions also arise where certain species don’t rely on their snouts for procuring or breaking down food. Humans, with relatively short faces compared to their large braincases, exemplify this, using hands, tools, and culinary skills instead.

In essence, our exploration establishes a new framework for comprehending face length variations among mammalian groups, potentially offering insights into the feeding habits of extinct megafauna. So, the next time a horse is asked “why the long face?” by a bartender, it might whimsically reply, “because I can afford it” – a nod to the evolutionary advantage of a longer face, leaving behind a generous tip.

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