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On Jaws, Noses, and Blowholes

Onions and garlic sauteed in the pan. Apple pie, fresh out of the oven. Fresh rain, freshly cut grass, campfires in the summertime. Rose, lavender, or (insert your favorite flower here). Now imagine not being able to flare your nostrils, to sniff, to take in the above odors in all their splendor.

Hard to fathom, right?

Smells fill our nostrils and linger on in memories, giving shape to us as individuals and as a species. Our strong sense of smell, and its partner in crime, sniffing, are products of a motile nose. And motile noses—noses that are a) capable of movement and b) separate from the upper jaw—are one of the traits that make mammals, well, mammals. Reptiles´ nose and upper jaw, on the other hand, are fused.

However, in a study published recently in Proceedings of the National Academy of Sciences, a team of researchers from the University of Tokyo determined that modern-day mammal noses come from ancient reptile jaws.

Take a jaw from reptile and mammal fossils and you will find the same amount of bones. In fact, the traditional understanding is that reptile and mammal jaws develop in the same way. The study, which tracked cells in the developmental stage in chickens, mice, and gecko embryos, showed otherwise.

The researchers honed in on a specific area called the frontonasal prominence. They stained the cells and tracked them as they grew. The group of cells would go on to form the jaw tips in reptiles, and the nose in mammals. Mammals´ jaw tips develop from a different cluster of cells altogether, known as the maxillary prominence.

So what's going on here? “As species’ ancestors accumulated more physical and genetic differences, the bone at the tip of reptiles’ upper jaw, the premaxilla, became smaller and migrated upwards,” said the University of Tokyo team. The bone that was behind it, the septomaxilla, became larger and moved forward to become the mammals´ jaw tip.

The study is a reminder that before we became a walking, talking, and thinking host of 206 bones, we were wads of cells. As the example of the frontonasal prominence shows, over the course of time, those cells zig, while others zag. What is a jaw at one point may become a nose at a later date.


In other nosey news, scientists at the University of Washington undertook a study to understand how noses transform into blowholes.

The study examined a group of marine mammals called cetaceans. Cetaceans, which include whales and dolphins, are thought to have evolved from land-walking mammals around 50 million years ago. Those mammals had forward-pointing noses. And as humans can attest, forward-pointing noses are not so practical in a life aquatic.

Researchers studying spotted dolphin and fin whale embryos found that in the early stages of development, they would form a nose, like any other mammal. By birth, it becomes a blowhole.

It turns out that different cetacean species evolved different ways to do it.

“The dolphin species and other toothed whales showed backwards bending of the skull, whereas the fin whale and other baleen whales showed changes in the occipital bone at the back of the skull,” said lead author Rachel Roston.

Ṛolston says more research is needed to confirm her hypothesis that there are multiple paths evolution can take to achieve the same outcome—in this case, the blowhole.

But for now, we know: somewhere, at a microscopic level, changes are underfoot.






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