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Updated: May 11, 2026
11:27
Selective Tracing of Auditory Fibers in the Avian Embryonic Vestibulocochlear Nerve
Published on: March 18, 2013
Mosaic evolution of the mammalian auditory periphery
1Department of Neuroscience, Carl von Ossietzky University Oldenburg, Oldenburg, Germany. geoffrey.manley@uni-oldenburg.de
Advances in Experimental Medicine and Biology
|May 30, 2013
Summary
The mammalian auditory system evolved gradually over millions of years, with key features like the three-ossicle middle ear and coiled cochlea developing independently due to changing environmental pressures and anatomical adaptations.
Area of Science:
- Evolutionary biology
- Paleontology
- Comparative anatomy
Background:
- The classical mammalian auditory periphery, characterized by a three-ossicle middle ear and coiled cochlea, is not a universal trait across all mammals.
- Auditory structures in mammals evolved over an extended period, with different components arising at distinct evolutionary times.
Purpose of the Study:
- To review the evolutionary timeline of mammalian auditory periphery constituents.
- To explore the selective pressures driving the evolution of the three-ossicle middle ear and coiled cochlea.
- To clarify that not all mammals share the same auditory periphery structure.
Main Methods:
- Review of existing paleontological and anatomical data.
- Analysis of evolutionary timelines spanning 230 million years.
- Comparative study of auditory structures across mammalian lineages.
Main Results:
- Mammalian middle ears evolved de novo, not through a single-ossicle intermediate, influenced by dietary shifts in early ancestors.
- The coiled cochlea evolved approximately 60 million years after the middle ear, driven by cochlear bone changes for improved impedance matching in therian ancestors.
- Significant diversity exists in mammalian auditory periphery structures, even among modern species.
Conclusions:
- The evolution of the mammalian auditory system was a protracted, non-linear process with distinct selective pressures acting on different components.
- The specific configuration of the auditory periphery in therian mammals is a result of unique evolutionary pathways not shared by all mammals.
Related Concept Videos
01:13The Cochlea
The cochlea is a coiled structure in the inner ear that contains hair cells—the sensory receptors of the auditory system. Sound waves are transmitted to the cochlea by small bones attached to the eardrum called the ossicles, which vibrate the oval window that leads to the inner ear. This causes fluid in the chambers of the cochlea to move, vibrating the basilar membrane.
01:15Auditory Pathway
Auditory pathways constitute the complex neural circuits responsible for transmitting and interpreting auditory information from the peripheral auditory system to the brain. Sound waves are initially captured by the outer ear, funneled through the ear canal, and reach the tympanic membrane (eardrum). These vibrations are transmitted via the middle ear's ossicles to the inner ear's cochlea.
When viewed cross-sectionally, the cochlea reveals the scala vestibuli and scala tympani flanking the...
When viewed cross-sectionally, the cochlea reveals the scala vestibuli and scala tympani flanking the...
01:16Anatomy of the Ear
Auditory sensation, commonly called hearing, involves the transformation of sonic waves into neural impulses facilitated by the structures of the auditory organ. The prominent, flesh-like structure on the side of the head, called the auricle, directs sound waves towards the auditory canal. The auricle is often mislabeled as the pinna, a term more aligned with mobile structures like a feline's external ear. The auditory canal penetrates the cranium via the external auditory meatus of the...
01:54Convergent Evolution
Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.
01:11The Auditory Ossicles
The auditory ossicles of the middle ear transmit sounds from the air as vibrations to the fluid-filled cochlea. The auditory ossicles consist of two malleus (hammer) bones, two incus (anvil) bones, and two stapes (stirrups), one on each side. These bones develop during the fetal stage and are the ones to ossify first. They are fully mature at birth and do not grow afterward.
The aptly named stapes look very much like a stirrup. The three ossicles are unique to mammals, and each plays a role in...
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01:22Hair Cells
Hair cells are the sensory receptors of the auditory system—they transduce mechanical sound waves into electrical energy that the nervous system can understand. Hair cells are located in the organ of Corti within the cochlea of the inner ear, between the basilar and tectorial membranes. The actual sensory receptors are called inner hair cells. The outer hair cells serve other functions, such as sound amplification in the cochlea, and are not discussed in detail here.