A new study led by researchers from the University of Washington has revealed how early mammals developed the ability to swallow like their modern descendants. The study, published in the journal *Current Biology*, analyzed a fossilized skull of a shrew-like mammal that lived 164 million years ago.
The fossil, known as *Eodelphis titijahensis*, is the earliest known example of a mammal with a fully formed stapes, a small bone in the middle ear that is essential for hearing and balance. The stapes is also responsible for transmitting sound vibrations from the eardrum to the inner ear.
In modern mammals, the stapes is attached to the incus, another bone in the middle ear, by a small ligament called the stapedial artery. This ligament helps to stabilize the stapes and allows it to move freely. However, in *Eodelphis*, the stapedial artery is not present.
The researchers believe that the absence of the stapedial artery in *Eodelphis* suggests that early mammals may have had a different way of hearing and balancing than modern mammals. They propose that early mammals may have used a different ligament or muscle to stabilize the stapes.
The study also found that *Eodelphis* had a relatively small inner ear compared to modern mammals. This suggests that early mammals may have had a less sensitive sense of hearing than modern mammals.
The findings of this study provide new insights into the evolution of hearing and swallowing in mammals. They suggest that early mammals may have had a different way of hearing and balancing than modern mammals and that they may have had a less sensitive sense of hearing.
The findings of this study have implications for our understanding of the evolution of mammals. They suggest that early mammals may have been less specialized than modern mammals and that they may have had a wider range of adaptations. This could help to explain why mammals were able to survive the extinction event that wiped out the dinosaurs 66 million years ago.
The stapedial artery is a key structure in the middle ear that helps to transmit sound vibrations from the eardrum to the inner ear. In most mammals, the stapedial artery is attached to the stapes, a small bone in the middle ear. However, in *Eodelphis*, the stapedial artery is not present. This suggests that early mammals may have had a different way of transmitting sound vibrations to the inner ear.
The absence of the stapedial artery in *Eodelphis* also has implications for our understanding of the evolution of hearing in mammals. In modern mammals, the stapedial artery helps to stabilize the stapes and allows it to move freely. Without the stapedial artery, the stapes may not have been able to move as freely, which could have affected hearing sensitivity.
The findings of this study provide new insights into the evolution of hearing and swallowing in mammals. They suggest that early mammals may have had a different way of hearing and balancing than modern mammals and that they may have had a less sensitive sense of hearing. These findings could help to explain why mammals were able to survive the extinction event that wiped out the dinosaurs 66 million years ago.
