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A new study has revealed the mysterious evolution of whale skulls



Some whales are dirty. You may not be able to watch them, but their skulls are truly incredibly asymmetrical. This mysterious feature helps with echolocation, the way whales work where things are, making sounds and capturing how they bounce back.

But this excavation is not present in all whales. My colleagues and I have recently done research to find out why and when wolf whales began to develop differently from their symmetrical cousins. We now know that whale skulls first appeared about 30 million years ago and that they became even more asymmetrical as creatures evolved into the modern species we know today.

To understand how whales got this way, we need to look at how they lived and adapted in the past. Fortunately for us, the fossil whale documentation is so remarkably represented that scientists have even described the whale as a “posterchild of development.”

; Whole skulls and skeletons stretch from the oldest whales 50 million years ago, and in the history of whales, other fossils are scattered to the living animals we know today.

3D scan of the skull skull showing asymmetry
Asymmetric skull skull – red arrows highlight oblique bones.
Ellen Coombs / UCL. The author provided

Thanks to this record, we are able to see the whales’ nostrils moving from the tip of their snout to the top of their head, an evolutionary tactic that makes it easier to breathe on the water surface. And the skulls of whales with teeth (which technically include dolphins as well as species such as sperm whales) have become more scaly, with bones on one side in different positions and the same bones on the other.

This is due to the amount of adipose tissue called “melon” that toothed whales use for echolocation. The melon and soft tissue needed for echolocation are placed to the left above the skull of the jagged whales, giving them an onion-shaped forehead and also causing the bones in the skull below it to grow to the left. As toothed whales evolved, their skulls became rougher.

But why don’t all whales have this curiosity? The first whales were called “archaeologists” (which literally means “ancient whales”). After about 8 million years, walking from land to water became completely watery.

We know that fossil archeological finds have whimsical sets (or snouts). It may be a distortion of fossils or a feature that has helped archaeologists figure out which directional sounds are coming from the water.

Skeleton of a four-legged creature.
Ambulocetus natans, the ancestor of whales.
Ghedoghedo, CC BY-SA

Then, about 39 million years ago, whales were divided into two groups: those with teeth in their mouths, known as “odontocetes,” and those with baleen (lines of bristles that allow whales to filter food out of the water), known as “mysticetes.” .

At one point, toothed whales developed dirty skulls and echolocation. However, mystics, including bald whales (such as blue whales), have diverged in a completely different evolutionary way. They have developed baleen and filtered fodder and skulls that are more symmetrical than archaeological finds, as well as toothed whales.

We wanted to understand why and exactly when it happened. To monitor the asymmetry in the development of the skull whale, we made a 3D scan of 162 skulls, of which 78 were fossil. By mapping this reversible change in the shape of the skull across the pedigree of whales, we were able to follow exactly when it first appeared in evolutionary history and in which family it evolved.

Asymmetry appears

Based on analyzes of these skulls, it appears that nasophacial asymmetry (reversibility) first developed about 30 million years ago. It was after the transition from archeological fairs to modern whales and after the division of odontets and mystics. Around the same time that this curiosity appeared, these early toothed whales developed by high-frequency hearing and complex echolocation.

We also confirmed that the early ancestors of live whales had little cranial asymmetry in the nasophacial region and were probably unable to echolocate. Therefore, it is likely that bald whales have never been able to echolocate.

Surprisingly, this asymmetry has reached its highest levels in some specific animals, such as sperm whales and narwhals and other species that live in deep or extreme environments.

This suggests that animals living in these complex environments, including belugs that live in icy, crowded waters, and river dolphins that live in shallow, muddy rivers, have developed different echolocation abilities, such as a more diverse or discreet sound repertoire that helps them when navigating and hunting, and with it the bones around the nose and face are more asymmetrical.

This evolutionary path of toothed whales is becoming increasingly asymmetric, suggesting that their skulls and overlapping soft tissues may continue to win as their echolocation techniques become more specialized.

These findings remind us not only of the complex evolutionary pathways that whale mammals have gone through to become the highly adapted iconic inhabitants of the oceans we know today, but also that despite living alongside some of the largest animals that ever existed, there are still many to we learned about them.


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