Ever wondered why swallowing seems so effortless? The key lies in our evolutionary past, where our cetacean ancestor, predating true mammals by millions of years, possessed sublingual bones. These bones, dating back 165 million years, have been a crucial factor in the success of mammals’ global proliferation.
Sublingual bones, scientifically known as hyoids, reside at the juncture of the esophagus and larynx behind the throat, aiding in the movement and swallowing of chewed food and liquids. While all mammals share the practice of feeding on colostrum, unlike other vertebrates, we distinguish ourselves by chewing food and swallowing it in small portions.
Microdocodon gracilis, our mammalian ancestors, were the size of contemporary rodents, and their fossilized remains in China provided an unprecedented glimpse into perfectly preserved sublingual bones. A study published in the journal Science (July 2019) highlighted that these bones replicate the shape of modern mammalian hyoids.
Mammals owe their diverse and widespread existence to the flexibility of hyoid bones. The ability to choose varied foods throughout evolution, be it insects, worms, meat, or plants, has been crucial. While modern species exhibit distinct tooth shapes based on their diets, the fundamental act of chewing and swallowing is universally enabled by the flexible hyoid bones situated behind our larynx. Zhe-Xi Luo, a professor at the University of Chicago, emphasizes this point, stating that the unique ability of mammals to chew and swallow is facilitated by these flexible hyoid bones.
All jawed animals, from fish to humans, possess hyoids, but the mammalian variant stands out for its remarkable flexibility. Ancestors of mammals from the Jurassic period (201-145 million years ago) displayed diverse dietary habits and tooth forms, suggesting the existence of flexible hyoids. The recent discovery of perfectly preserved sublingual bones in Microdocodon gracilis has unraveled this evolutionary mystery that remained unknown until now.
