All the better to hear you with: Experts find ancient fossils in China that are a ‘missing link’ in the evolution of modern mammal ears from jaw bones
- The three tiny bones in our inner ear that allow us to hear started out differently
- In our ancient ancestors, hearing was achieved using the bones of the jaw
- Origolestes lii lived more than 100 million years ago near what is now Jinzhou
- Its hearing bones had just detached from each other and the cartilage of the jaw
Experts have found the fossils of an ancient mammal species in China that is a ‘missing link’ in the evolution of modern ears from jaw bones.
The tiny bones in our ears are known to have evolved out of the jawbones of our ancient ancestors, but the steps along this process had remained elusive.
In the newly-identified transitional species, however, the hearing bones appear to have begun their isolation from each other and the cartilage of the jaw.
This first decoupling — which took place over 100 million years ago — freed chewing and hearing from each other and let them develop into their modern forms.
Experts have found the fossils of an ancient mammal species in China — pictured centre in this artist’s reconstruction — that is a ‘missing link’ in the evolution of modern ears from jaw bones
Modern mammals. including us humans. owe our sense of hearing to the three tiny but intricate bones of the middle ear — dubbed the ‘ossicles’ — which are commonly referred to as the hammer, anvil and stirrup.
These bones take sound waves passing through the air and — passing the vibrations through each of the three bones in turn — transmit such into fluid waves inside the inner ear.
Here, the waves in the snail-shaped inner ear vibrate and are detected by hair cells and turned into electric signals which our brains can interpret as sound.
Originally, however, the ossicles formed part of the jaw which — for our earliest ancestors — was used to both hear as well as to chew.
While the evolution of these jaw bones into a complex hearing apparatus is taken as fact by the scientific community, fossil examples that show the intermediate stages between the two have been elusive.
Palaeontologist Fang-Yuan Mao of the Chinese Academy of Science and colleagues report the discovery of a new species and genus of mammal from the Yixian rock formation near the Chinese city of Jinzhou.
The animal — dubbed Origolestes lii — would have lived during the Early Cretaceous Period, around 146–100 million years ago.
O. lii sports detached hearing bones that represent a key and previously unseen step in the evolution of the modern mammal ear.
This initial separation of hearing and chewing functions served to remove the constraints each imposed on the other, allowing both to be improved.
Origolestes lii, whose fossil remains are pictured, would have lived during the Early Cretaceous Period, around 146–100 million years ago
Origolestes lii, pictured in this artist’s reconstruction, sports detached hearing bones that represent a key and previously unseen step in the evolution of the modern mammal ear
In the newly-named transitional species the hearing bones (highlighted in pink and yellow) appear to have begun their isolation from each other and the cartilage (purple) of the jaw
The researchers analysed the fossil remains of O. lii in detail — taking high-resolution CT scans — allowing them to understand the nature of the mammal’s auditory bones and cartilage.
They found that the animals hearing bones lacked the bone-on-bone contact seen in species that came from earlier points in time.
The full findings of the study were published in the journal Science.
The researchers analysed the fossil remains of O. lii in detail — taking high-resolution CT scans, pictured — allowing them to understand the mammal’s auditory bones and cartilage
Palaeontologist Fang-Yuan Mao of the Chinese Academy of Science and colleagues report the discovery of a new species and genus of mammal from the Yixian rock formation near the Chinese city of Jinzhou