Dr. Bill Kobb
Level of Cherry Feather
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- Sep 5, 2003
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Fish fossil confirms origin of nostrils
Land vertebrates can breathe through their noses thanks to an anatomical rearrangement of fish-style nostrils. That same rearrangement may explain why cleft lips and cleft palates are common birth defects in humans. The nasal passages of land vertebrates differ dramatically from their fish ancestors. In fishes, the nose is independent of the mouth and throat. Water enters the nasal sac through one pair of nostrils and exits through a second pair.
By contrast, land vertebrates - technically known as tetrapods, because of their four limbs - have nasal passages that open to the outside world through a pair of external nostrils, and to the throat through a pair of internal nostrils or choanae. Many biologists suspect the choanae evolved from one pair of fish nostrils that migrated over millions of years to a new position inside the throat. To do that, however, the nostrils would have had to cross through the line of teeth at some point, a move that sceptics regarded as unlikely.
Perfect intermediate
Their doubts should vanish, thanks to a careful reconstruction of several fossilised skulls of the most primitive known ancestor of tetrapods, a fish known as Kenichthys campbelli, from Yunnan, China. In Kenichthys, the second pair of nostrils opens neither externally nor internally, but directly into a gap in the row of teeth (Nature, vol 432, p 94).
“It’s as if we were to have a nostril located on the upper jaw margin between the canine and the adjacent incisor,” says Per Ahlberg of Uppsala University in Sweden, who did the study with Min Zhu of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing.
In short, Kenichthys is a perfect intermediate, says John Maisey, a vertebrate palaeontologist at the American Museum of Natural History in New York. Developing human embryos have a gap in the same place in the upper jaw, which later fuses. If it fails to fuse, the result is a cleft palate or cleft lip. Most likely, then, these birth defects arise from the same developmental process that gave us the ability to breathe through our noses, says Ahlberg.
http://www.newscientist.com/news/news.jsp?id=ns99996607
Land vertebrates can breathe through their noses thanks to an anatomical rearrangement of fish-style nostrils. That same rearrangement may explain why cleft lips and cleft palates are common birth defects in humans. The nasal passages of land vertebrates differ dramatically from their fish ancestors. In fishes, the nose is independent of the mouth and throat. Water enters the nasal sac through one pair of nostrils and exits through a second pair.
By contrast, land vertebrates - technically known as tetrapods, because of their four limbs - have nasal passages that open to the outside world through a pair of external nostrils, and to the throat through a pair of internal nostrils or choanae. Many biologists suspect the choanae evolved from one pair of fish nostrils that migrated over millions of years to a new position inside the throat. To do that, however, the nostrils would have had to cross through the line of teeth at some point, a move that sceptics regarded as unlikely.
Perfect intermediate
Their doubts should vanish, thanks to a careful reconstruction of several fossilised skulls of the most primitive known ancestor of tetrapods, a fish known as Kenichthys campbelli, from Yunnan, China. In Kenichthys, the second pair of nostrils opens neither externally nor internally, but directly into a gap in the row of teeth (Nature, vol 432, p 94).
“It’s as if we were to have a nostril located on the upper jaw margin between the canine and the adjacent incisor,” says Per Ahlberg of Uppsala University in Sweden, who did the study with Min Zhu of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing.
In short, Kenichthys is a perfect intermediate, says John Maisey, a vertebrate palaeontologist at the American Museum of Natural History in New York. Developing human embryos have a gap in the same place in the upper jaw, which later fuses. If it fails to fuse, the result is a cleft palate or cleft lip. Most likely, then, these birth defects arise from the same developmental process that gave us the ability to breathe through our noses, says Ahlberg.
http://www.newscientist.com/news/news.jsp?id=ns99996607
