Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Swedish-Chinese research team uncovers the history of the nose

04.11.2004


Our ancestors had two nostrils, one front and one back, but no opening on the palate or in the throat. They could smell, but not breathe with their nose. How did our nose evolve? Per Ahlberg, Uppsala university, and Zhu Min, department of Vertebrate Paleontology in Beijing, China, has now found a fossil that explains the history of the nose.



Have you ever wondered, taking a deep breath of fresh autumn air and sensing how the smell of wet leaves tickles your nose, just how it came about that you can do so? We humans take it for granted that our nose forms a passage between the world around us and our windpipe, but this hasn’t always been the case. We land-based vertebrates or “tetrapods” (mammals, birds, reptiles, and amphibians) originally descend from fish, and fish cant breathe through their nose. On the side of a fish’s head there are two nostrils, one front and one back, that form the opening to a little sac containing the olfactory organs: water flows in through the front nostril and out through the back one, but there is no connection whatsoever to the throat. In other words, fish can smell with their nose, but not breathe.

We tetrapods may have only one external nostril on each side of our head, but we do have an inner nostril or “choana” that opens on the palate or in the throat. This is what makes it possible for us to breathe through our nose. But how did this inner nostril evolve? One thing all scientists agree about is that the front nostril in fish corresponds to our single outer nostril: the question is whether the back nostril was transformed into our choana by “migrating” to the palate, or whether the choana is a new opening that arose with tetrapods.


The answer to that question is of importance to a greater issue, namely, how large-scale evolution actually functions. This is the part of evolution that is perhaps most difficult to understand. Its easy for us to imagine how evolution deals with small steps, like developing a blue tit and a great titmouse from a common ancestor (this merely involves small details in plumage and size), but how does a nostril move from the face to the palate? Some scientists have claimed that it is impossible for an outer nostril to gradually migrate to the palate, since a “cord” of nerves and blood vessels runs just inside the row of teeth that the nostril would have to sever during its migration. The “cord” is in evidence both in fish and tetrapods, so it appears that nothing has happened to it during our evolution.

In a pinch like this, it is natural to turn to fossils to see what they can tell us, but thus far it hasnt been of much use. Among fossil “coelacanth” fish, which are the closest relatives of tetrapods, some forms have two outer nostrils but no choana, just like modern fish. Other fossil coelacanths, which are even closer to tetrapods, already have a single outer nostril per side and a fully developed choana. In other words, the fossils show that the choana emerged just before our ancestors crawled up onto land, but they tell us nothing about how the choana came to be formed.

Now two researchers, Per Ahlberg from the Department of Physiology and Developmental Biology, Uppsala University, and Zhu Min from the Department of Vertebrate Paleontology in Beijing, China, are able to present a unique fossil that clarifies once and for all how our inner nostril came into being. Their results are being published this week in the internationally respected scientific journal Nature.

The fossil is a small coelacanth fish, Kenichthys campbelli, which comes from China and is roughly 400 million years old. The scientists have found skulls of several individuals: some of the bones have fallen apart, but they are so well preserved that it is possible to see exactly how they fit together. Judging from their features, Kenichthys belongs in our ancestral tree between the fossil coelacanths who have no choana and those that have this inner nostril.

Kenichthys has a back nostril that is located right on the lip, separating the two-toothed upper jawbones, the maxillan and the premaxillan. (It is as if we were to have a nostril in a gap between our front teeth and our canine teeth.) In other words, it constitutes a perfect halfway point in the nostrils migration from the face to the palate, and moreover this halfway point is the precisely the one that some scientists have regarded as an anatomical impossibility. Unfortunately the “cord” of nerves and blood vessels has not been preserved in Kenichthys, but since it normally runs from the maxillan to the premaxillan, it must either have been cut off or relegated to another position. What was considered impossible was apparently possible after all.

At this stage we still don´t know how evolution managed to re-forge the contact between the maxillan and the premaxillan and re-establish the “cord” after the nostril had migrated past. Zhu and Ahlberg hope that future developmental biological research will be able to identify the molecular mechanisms that govern the formation of this section of the head. One thing is already apparent: there is a connection between the migration of the nostril in our ancestors and the rather common problem in human developmental biology that is termed “cleft jaw”.

During the development of the human fetus, the upper jaw is formed when two processes, which will form the maxillan and the premaxillan respectively, meet under the outer nostril and grow together. In this way they separate the outer nostril from the choana. If this coalescing process does not function, a so-called “cleft jaw” is formed, that is, a furrow that runs right up into the nasal sac. This “complicated” relationship between the upper jaw and the nasal sac does not exist in fish: after all, they have no nostril on the palate, so the upper jaw is quite simply formed below the nostrils without any problematic process of coalescence. It seems as if our complicated developmental process is a “memory” of how the back nostril made its way to the palate between the maxillan and the premaxillan, and then reconnoitered again behind it. Somewhat drastically it could be said that the intermediate form Kenichthys lived with a cleft jaw all its life. Thus a really old fossil fish can elucidate not only an important aspect of our early evolution but also the reasons behind one of the most common problems of human developmental biology.

Anneli Waara | alfa
Further information:
http://www.uu.se
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v432/n7013/abs/nature02843_fs.html

More articles from Life Sciences:

nachricht The irresistible fragrance of dying vinegar flies
16.08.2017 | Max-Planck-Institut für chemische Ökologie

nachricht How protein islands form
15.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

Im Focus: Scientists improve forecast of increasing hazard on Ecuadorian volcano

Researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, the Italian Space Agency (ASI), and the Instituto Geofisico--Escuela Politecnica Nacional (IGEPN) of Ecuador, showed an increasing volcanic danger on Cotopaxi in Ecuador using a powerful technique known as Interferometric Synthetic Aperture Radar (InSAR).

The Andes region in which Cotopaxi volcano is located is known to contain some of the world's most serious volcanic hazard. A mid- to large-size eruption has...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

New thruster design increases efficiency for future spaceflight

16.08.2017 | Physics and Astronomy

Transporting spin: A graphene and boron nitride heterostructure creates large spin signals

16.08.2017 | Materials Sciences

A new method for the 3-D printing of living tissues

16.08.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>