Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Did our ancestors breathe through their ears?

19.01.2006


A fossil fish skull from Latvia that researchers from Uppsala University, Sweden, describe in this weeks issue of Nature shows that the earliest land animals probably breathed through their ears.



"It looks as if the first step in the evolution of the middle ear had nothing to do with hearing. Our forebears developed ears in order to breathe through them," says Professor Per Ahlberg.

The human sense of hearing is based on the interaction of two different organs: the inner ear and the middle ear. The inner ear contains sensory cells that capture sound vibrations and send them on as nerve impulses to the brain. The middle ear is an ingenious mechanical audio amplifier that captures the weak sound vibrations in the air with a membrane (the eardrum), amplifies them with a leverage system (ear bones) and sends them on to the inner ear. Without the middle ear, the inner ear would not function.


All vertebrates have inner ears, but the middle ear exists only in land animals. Fish dont need middle ears since sound vibrations are stronger in water and easily pass through the body of a fish. The construction of the middle ear differs, however, among different groups of land animals: mammals have an eardrum and three ear bones (hammer (malleus), anvil (incus), and stirrup (stapes)), while birds, reptiles, and frogs have only one ear bone (stirrup) that connects the eardrum directly to the inner ear. But it is questionable whether the eardrums in mammals, reptiles, and frogs are identical or whether they arose independently of each other.

A comparison with fish muddies the picture even further: instead of middle ears, fish have a little gill, the blow-hole, that isnt covered by an eardrum but rather forms an open canal between the throat and the outside of the head. The equivalent of the stirrup, the hyomandibula, supports the gill lid but has no contact with the inner ear. Neither the hyomandibula nor the blow-hole plays any role in hearing.

These differences make it difficult to understand how the middle ear arose. How could evolution change both the structure and function of the fishes‚ blow-hole so radically? Did the earliest land animals have a sound amplifying middle ear at all? The earliest fossil land vertebrates or tetrapods, like Acanthostega from Greenland (that lived roughly 360 million years ago), had a stirrup that was in contact with the inner ear, but it was large and clumsy and appears not to have been connected to the eardrum. They also had a couple of round Œoutlets‚ in the rear edge of the skull: in modern frogs the corresponding outlet is the fastening point for the eardrum, but in fish it is the site of the outer opening of the blow-hole. This combination of characteristics has led to the hypothesis that the earliest land animals still had open blow-holes and perhaps breathed through them.

The Uppsala scientists‚ new data strongly support this hypothesis. The information comes from the skull of a Panderichthys from Latvia, the fossil fish that is closest to the emergence of land animals. It has been known that Panderichthys had a hyomandibula, and it was generally assumed that its blow-hole was of the normal fish type. But this is not the case: in actual fact the hole is similar to the middle ear‚ of a tetrapod like Acanthostega. Since the hyomandibula of the Panderichthys had no contact with the inner ear, its blow-hole could hardly have had a sound-amplification function.

"Thus the transformation of the form of the blow-hole must have been caused by another driving force than the improvement of hearing," says Per Ahlberg.

Compared with closely related fish, the blow-hole in Panderichthys has a considerably larger diameter and is furthermore both shorter and straighter. It looks like an adaptation to active breathing (of either water or air) through the blow-hole, compared with ordinary‚ fish in which only a small portion of breathing water passes through this hole. A similar adaptation can be seen in modern rays, which have a very large blow-hole.

Since the middle ear‚ in the earliest tetrapods has the same form as the blow-hole‚ in Panderichthys, it seems likely that they retained the breathing function. But in tetrapods the gill lid is gone and the hyomandibula is transformed into a primitive stirrup. The fact that the stirrup has contact with the inner ear indicates that a rudimentary hearing function had also been added.

"We can speculate about how this came about. The blow-hole of a fish can be closed by a valve muscle on top. If an early tetrapod did the same thing, a truly enclosed middle ear was temporarily created, where the stirrup, which probably supported the wall of the middle ear, could forward vibrations from the middle ear to the inner ear. When the hearing function eventually became more important, the blow-hole was permanently closed by an eardrum," reasons Per Ahlberg.

The article is being published in Nature on January 19.

Anneli Waara | alfa
Further information:
http://www.uu.se
http://www.nature.com

More articles from Life Sciences:

nachricht Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs
16.01.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Cholera bacteria infect more effectively with a simple twist of shape
13.01.2017 | Princeton University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Solar Collectors from Ultra-High Performance Concrete Combine Energy Efficiency and Aesthetics

16.01.2017 | Trade Fair News

3D scans for the automotive industry

16.01.2017 | Automotive Engineering

Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs

16.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>