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The mysterious evolution of whale skulls was revealed by a new study



Some whales are banal. You may not know you are looking at them, but their skulls are actually incredibly asymmetrical. This mysterious feature helps with echolocation – whales work where they are, making sounds and feeling them reflected back.

However, these surprises are not present in all whales. We recently conducted research with colleagues to find out why and when whales began to evolve differently from their symmetrical cousins. We now know that extraordinary whale skulls first appeared about 30 million years ago and that as creatures evolved into the modern species we know today, they became even more asymmetrical.

To understand how crazy whales got in this way, we needed to look at how they lived and adapted in the past. Fortunately for us, the record of whale fossils is so remarkably significant that scientists have even called the whale a “evolutionary poster.”

; Full skulls and skeletons stretch directly to the earliest whales 50 million years ago, and more fossils are points throughout the history of whales, to the live animals we know today.

3D scan of the Narval skull showing asymmetry
Asymmetrical narwhal skull – red arrows highlight distorted bones.
Ellen Coombs / UCL, Submitted by the author

With this record, we see that the nostrils of whales have moved from the tip of the muzzle to the top of the head, an evolutionary tactic that allows easy breathing on the surface of the water. And whale skulls with teeth (which technically belong to dolphins, as well as species such as sperm whales) have become slimmer when the bones are in different positions on one side and the bones on the other side.

This is due to the mass of adipose tissue called melon, which toothed whales use for echolocation. The melon and soft tissues needed for echolocation are placed to the left above the skull on the toothed whales, giving them an onion forehead, and the bones at the bottom of the skull shift to the left. With the development of toothed whales, their skulls became amazing.

But why aren’t all whales so amazing? The first whales were called “archaeocetes” (which literally means “ancient whales”). They have changed from walking on land to full water over a period of about 8 million years.

We know that archaeocyte fossils have lustful flowers (or muzzles). This may be a distortion of the fossils or a feature that has helped archaeochetes determine which direction the sounds are emanating from the underwater.

Skeleton of a quadruple whale-type creature.
Ambulocetus natanai, the early ancestor of whales.
Ghedoghedo, CC BY-SA

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

At some point, toothed whales developed gloomy skulls and echolocation. However, the mysteries, which include the great whale whales (e.g., the Blue Whale), have strayed in a completely different path of evolution. They created a baleen and filter feed and a skull that is more symmetrical than archaeocetes and toothed whales.

We wanted to understand why and when exactly this happened. Thus, to observe the asymmetry in the evolution of the whale skull, we developed 3D scans from 162 skulls, 78 of which were fossils. By mapping this amazing change in the shape of the skull through the tree of the whale family, we were able to trace exactly when it first appeared in the history of evolution and in which families it evolved.

An asymmetry occurs

Based on the analysis of these skulls, it appears that the asymmetry (astonishment) of the nasal face appeared about 30 million years ago. This occurred after the transition from archaeocetes to modern whales and after the decay between odontocetes and mystics. Around the time this marvel appeared, these early serrated whales developed for high-frequency hearing and complex echolocation.

We also confirmed that the early ancestors of live whales did not have skull asymmetry in the nasal facial area and probably failed to perform echolocation. So most likely baleen whales have never been able to echo location.

Most surprisingly, this asymmetry has reached its highest level for some specific animals, such as sperm whales and cages, and other species living in deep or extreme environments.

This suggests that animals living in this complex environment, including icy, polluted waters, and river dolphins living in shallow, foggy rivers, have different echolocation capabilities, such as a more diverse or discrete repertoire of sound to help them navigate and hunt along with it. the bones around the nose and face became more asymmetrical.

This increasingly asymmetric evolutionary path of toothed whales suggests that their skulls and the soft tissues covering them may remain more amazing as their echolocation methods become more specialized.

These findings remind us not only of the complex evolutionary paths that cetaceans have gone through to become inhabitants of the well-known iconic oceans we know today, but also that, despite living with some of the greatest animals ever to exist, there are still a lot for us to learn about them.


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