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Breathing can only be studied indirectly in extinct groups of stegocephalians,
but we can infer that most had lungs, like lungfishes, some actinopterygians
(Polypterus), and most tetrapods. In addition to this, some groups had
larvae with external gills (temnospondyls, seymouriamorphs), although
the adults appear to have lost these structures. Cutaneous respiration
may have been possible in a few groups, but it was probably not widespread
because many stegocephalians were too large for this mechanism to work
well, and most were covered in bony scales that would have interfered
with gas exchange.
Most tetrapods breathe with the lungs that they inherited from their
sarcopterygian ancestors (lobe-finned fishes such as the coelacanth
and lungfishes). However, other respiratory structures also exist in
lissamphibians, and a few salamanders have even lost their lungs (Duellman
and Trueb, 1986). Other respiratory structures include external gills
(present in several salamanders and larval amphibians), the skin (in
many lissamphibians), and the buccopharyngeal cavity (in some frogs).
Amniotes have fewer respiratory structures, but some turtles can use
buccopharyngeal breathing to remain submerged for long periods of time
(Goin, Goin, and Zug, 1978).
Click on an image to view larger version & data in a new window
Figure 1. The plethontid salamander Ensatina eschscholtzi. Plethodontids
have no lungs; their gas exchange is accomplished by buccopharyngeal
and cutaneous breathing. Picture copyright © 1996, Charles Brown.
Duellman, W. E. & L. Trueb. 1986. Biology of Amphibians. New York: McGraw-Hill.
Goin, C. J., O. B. Goin, & G. R. Zug. 1978. Introduction to herpetology. 3 ed., Vol. 1. New York: W. H. Freeman and company.
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Muséum National d'Histoire Naturelle, Paris, France
Page copyright © 1996 Michel Laurin
Page: Tree of Life
Breathing in Stegocephalians
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