Some whales are picky. You may not know how to look at them, but their skulls are actually incredibly asymmetrical. This mysterious feature helps with echolocation, how whales work, where things are, making sounds and hearing them bounce back.
But this trick is not present in all whales. My colleagues and I recently conducted research to find out why and when fragile whales began to develop differently from their symmetrical cousins. We now know that bizarre whale skulls first appeared about 30 million years ago, and that they continued to become even more asymmetric as creatures evolved into the modern species we know today.
In order to understand how demanding whales got this way, we needed to look at how they lived and adapted in the past. Fortunately for us, the fossil record of whales is so well represented that scientists have even called the whale a “descendant of evolution.”; Whole skulls and skeletons date back to the earliest whales 50 million years ago, and more and more fossils are a dot in the history of whales, all the way to the living animals we know today.
With this record, we can see that the whales’ nostrils have moved from the tip of their snout to the top of their heads, an evolutionary tactic that allows them to breathe easily on the surface of the water. And the skulls of whales with teeth (which technically include dolphins, as well as species such as sperm whales) have become more oblique, with bones on one side in different positions to the same 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 located on the left above the skull on toothed whales, giving them a bulbous forehead, as well as forcing the skull bones to grow obliquely to the left below. When toothed whales evolved, their skulls won.
But why aren’t all whales so picky? The first whales were called “archeocetes” (which literally means “ancient whales”). They evolved from walking on land to full water in a relatively short 8 million years.
We know that the minerals of archeocetes have shaky tribunes (or muzzles). This may be a distortion of fossils or a feature that helped archaeologists determine in which direction the sounds come from underwater waters.
Then, about 39 million years ago, whales split into two groups: those with teeth in their mouths, known as “odontocytes, and those with whiskers” (rows of bristles that allow whales to filter food from the water), known as ” cities.
At some point, toothed whales evolved into fragile skulls and echolocation. However, mysteries, which include large baleen whales (such as blue whales), have diverged in a completely different evolutionary path. They developed whiskers and a feeding filter and skulls that are more symmetrical than archeocetes and toothed whales.
We wanted to understand why and when it happened. Thus, to track the asymmetry of the evolution of the whale’s skull, we created a 3D scan of 162 skulls, 78 of which were fossilized. Reflecting this unusual change in the shape of the skull in the family tree of whales, we could accurately trace when it first appeared in evolutionary history and in which families it developed.
Based on analyzes of these skulls, nasal-facial asymmetry (unworthiness) first developed about 30 million years ago. This was after the transition from archaeocets to modern whales and after the split between odontocetes and mysticists. Around the same time that this trick appeared, these early-toothed whales developed high-frequency hearing and complex echolocation.
We also confirmed that the early ancestors of live whales had a slight cranial asymmetry in the nasofacial region and were probably unable to echolocate. Thus, it is likely that baleen whales were never 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 conditions.
This suggests that animals living in these complex environments, including belugas living in icy, cluttered waters, and river dolphins living in shallow, muddy rivers, have developed other echolocation abilities, such as a more diverse or discrete sound repertoire. , which will help them navigate and hunt, and with it the bones around the nose and face have become more asymmetrical.
This evolutionary path of toothed whales is becoming increasingly asymmetric, suggesting that their skulls and covered soft tissues may continue to gain more and more advantageous power as their echolocation techniques become more specialized.
These findings remind us not only of the complex evolutionary paths that cetaceans have traveled to become the perfectly adapted iconic inhabitants of the ocean that we know of today, but that, despite living next to some of the largest animals that ever existed, , there is still a lot for us to learn about them.