The age-old joke, “A horse walks into a bar, and the bartender asks ‘why the long face?’” has a scientific basis. The reason for horses’ elongated faces?
Researchers have discovered that horses and other large mammals have elongated faces simply because they can. This phenomenon, known as “evolutionary craniofacial allometry” or ECA, is common in various mammalian groups like cats, rodents, deer, kangaroos, and some monkeys.
The ECA pattern might be a part of the innate development of the skull, meaning that a mammal’s face automatically becomes longer as the animal grows. However, there are exceptions where the ECA pattern either doesn’t exist or is reversed.
The answer might lie in the simple biomechanics of how species use their faces to eat. For instance, sheep and cows eat the same grass. However, because sheep are generally smaller, they need to bite harder with their jaws, jaw muscles, and teeth.
Shorter faces are more efficient at biting hard due to the shorter distance between the jaw muscles and the teeth. So, if short faces are so good at biting hard, why do large mammals have longer faces? The answer lies in the fact that larger animals naturally have larger muscles and can bite more easily.
Larger mammals “allow” themselves to have longer skulls, known for their advantages in various situations. In herbivores, longer faces facilitate reaching more leaves or taking larger bites. In carnivores, a longer face can make room for larger fangs in the mouth or can help the jaws close faster.
The researchers’ proposed explanation for ECA also explains the exceptions, which almost always involve a major dietary shift. For example, Potorous tridactylus “allows” itself to have longer faces than its larger relatives because they consume softer foods. A longer face may allow them to have a longer tongue or to sniff easily through the ground for food.
We also expect exceptions in cases where a species does not use its snout to catch or break down food. Humans, with their remarkably short faces compared to their huge cranial box, are an excellent example. Our species doesn’t use its face at all to obtain food; our hands, tools, and cooking ability do this for us.
The research offers a new framework for understanding face length in different groups of mammals. We could use this framework even to gain an important understanding of the feeding habits of extinct mega-fauna in Australia.
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