Adaptations to feeding may explain why large species of mammals — like, say, dolphins — often have much longer faces compared to smaller closely related species.
That pattern is called Craniofacial Evolutionary Allometry (CREA), and Dr. Rex Mitchell from Flinders University and a co-author of a new study says:
“The CREA pattern is seen across lots of different mammals that otherwise have little in common – from cats to mice, from antelopes to baboons, from deer to kangaroos. However, so far, scientists have not been able to explain what causes it.”
The team analyzed the skull shapes of 22 mammal families, and found that larger species within each family often had longer faces, but not always (e.g., the orca and Tasmanian devil are the largest species of their families, but have shorter faces).
On the other hand, senior author and Associate Professor Vera Weisbecker, also from Flinders University, adds:
“Confusingly, there are also many mammals where the rule does not hold up or is even reversed.
“Australian carnivorous marsupials are a great example. We found that their largest living member, the Tasmanian devil, has an exceptionally short face compared to other species.”
Co-author Dr. Emma Sherratt, from the University of Adelaide, says the team went back to basic “lever mechanics” to explain both the rule of the long face and its exceptions:
“Closely related mammals tend to eat similar foods. For example, different kangaroos species all eat grass or leaves and different species of wolves and foxes all eat meat. However, bigger animals of a group have a naturally stronger bite because their skull, teeth and jaw muscles are simply bigger.”
This means that smaller mammals need stronger bites to chew the same food as larger relatives. For this, shorter faces are advantageous because they can impart more bite force.
But what about those glaring exceptions? To which Weisbecker says:
“Our analyses of 22 mammal families show that there is almost always a radical change in diet when smaller mammals have longer faces than their larger relatives.
“For example, Tasmanian devils are known to crush bones, and the short-snouted orcas feed on much larger prey than their fish-eating dolphin relatives. These behaviors need higher bite forces.
“But this also works the other way around. For example, the tiny honey possum has a much longer snout than would be expected for any possum, but it also mostly licks nectar from deep inside flowers and does not need to bite hard.”
Check out the original study here.
