Evolution of Mammalian Face: How Did Mammals Develop Flexible Noses That Gave Them Strong Sense of Smell?

University of Tokyo researchers examined the evolution of facial structure by studying skeletons and embryos to discover how mammals have developed protruding and flexible noses that gave them a strong sense of smell.

Researchers said that the findings of the study help create potential new animal models, such as frogs and chickens, which are usually used in laboratory experiments to investigate facial development disorders, like cleft palate.

Tracking Facial Development in Cellular Experiments

According to Phys.org, it is a common scientific understanding of facial evolution that the jaws of mammals and reptiles developed in an almost similar way despite the former having a unique nose that has remained unknown for many years.

The study, titled "Mammalian Face as an Evolutionary Novelty," published in Proceedings of the National Academy of Sciences (PNAS), is the first research to examine the evolution of facial structure using cellular studies that compare multiple embryos of different species.

Researchers designed experiments that enabled them to track facial development in embryos of multiple species, such as chickens (birds), lizards (reptiles), and mice (mammals). Their study focused on a group of cells in embryos that provide the structures of the face.

They stained these cells in the embryos to track their growth and development. They noticed that the frontonasal prominence group formed into the jaws of reptiles but became a protruding nose to mammals. While a separate group of cells called the maxillary prominence formed into the jay tips in mammals.

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Examining Facial Development in Fossil Specimens

They used the information they gathered in examining the fossil specimens of the three species, wherein their ancestors have accumulated more physical and genetic differences.

For instance, the bone at the tip of the upper jaw of reptiles called premaxilla became smaller and moved upwards. The bone behind it, called septomaxilla, became larger and moved forwards that formed into the jaw tip of mammals.

Researchers said that the facial bones of platypus and echidna, who are both egg-laying mammals, provided an additional living example of transitional bone structures.

Separation of Nose and Jaw Gives Mammals Unique Sense of Smell

Researchers said in the press release of the university that the separation of the nose and jawbones give mammals their unique ability to sniff and sense of smell. Their muscles in the nostrils flare to inhale odors from the environment deeply.

Postdoctoral researcher and study author Hiroki Higashiyama said this finding is a key innovation in the evolution of the nose of the protruding and flexible noses of mammals. These unique characteristics of the mammalian nose help them distinguish and recognize various odors that may have helped them develop to become larger and have more complex brains than their ancestors.

Researchers noted that although the study provided physical evidence of the evolutionary shift in the premaxilla and septomaxilla arrangement, more genetic studies are needed. Nonetheless, scientists discovered the composition of facial prominences and embryonic development in multiple species that they can use to compare facial development disorders.

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