Where and how did mammals get their noses?

One of the traits that is unique to mammals is having a nose. I am not just talking about the nostrils, which lot’s of other vertebrates have as well. It’s the protruding and mobile (at least to some degree) structure of the mammalian face that includes the nostrils. Here a recent paper shows how this structure evolved from structures in the upper jaw.

The upper jaw consists of two major pairs of bones called the premaxilla and maxilla. The premaxiilla is the front-most portion of the upper jaw and at the back is the maxilla.The traditional view was that these bones developed in the same manner in both mammals and non-mammals. But it turns out that during the evolution of mammals, the premaxilla became increasingly smaller migrated upward and was eventually replaced by a bone in between these bones called the septomaxilla, which became the tip of the upper jaw. This caused the nose to seperate from the jaws, allowing mammals to sniff the air.

This is transition is seen in the fossil record, as well as the living monotremes (platypus and echidna).

And in embryological development.

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What I think is particularly interesting is that the mammalian premaxilla isn’t completely absent, it is just highly reduced and fuses to the septomaxilla, forming the palatal process of the mammalian “premaxilla”.
Where before there were two bones, one from the frontonasal prominence (premaxilla) and one from the maxillary prominence (septomaxilla), in mammals there is now one bone that forms from two separate ossification centres, one from the frontonasal prominence and one from the maxillary prominence, so it is still clear from development that one ossification centre has homology with the premaxilla and the other with the septomaxilla.

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Thanks for this. Really interesting!

Fred Hoyle and Chandra Wickramasinghe hypothesized that humans had noses that covered their nostrils to reduce exposure from the extraterrestrial viruses that constantly rain down from the sky and insert their genomes into our DNA.

In the race for survival, mammals win by a nose.

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The thing this thread makes me think of is the Monty Python sketch on the deadly joke the Allies wrote and translated into German in WWII. At one point it is said that the Germans are working on their own version of the joke, and Hitler is shown at a rally (in what is, I think, a clip from Triumph of The Will) declaring, “My dog’s got no nose!” A man from the crowd below responds, “How does he smell?” and Hitler replies, “Terrible!”

I know Wickramasinghe is a crackpot(he has also seriously suggested that diatoms detected in the atmosphere are aliens falling down to Earth in space-dust) but I didn’t know Hoyle had that fringe ideas too.

This thread is nosy.

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