Carrier's constraint

Ceramic tiles showing typical lizard's pattern of movement

Carrier's constraint is an observation about air-breathing vertebrates which flex their bodies sideways when moving. They find it very difficult to move and breathe at the same time. The sideways flexing expands one lung and compresses the other, shunting stale air from lung to lung instead of expelling it completely to make room for fresh air.^[1]

It was named, by English paleontologist Richard Cowen, after David R. Carrier, who wrote his observations on the problem in 1987.^[2][3][4]

Many amphibia and reptiles can and do move very fast over short distances. They do it by moving without breathing, which builds up an "oxygen debt". Humans sometimes do this when running very quickly. 100-metre sprinters do not breathe during a race. They collapse and recover afterwards.^[2] Many reptiles and amphibians are ambush predators, which fits that kind of life quite well. There is no reptile or amphibian equivalent to dogs or deer, with their huge capacity for running long distances.

There are, however, some reptiles which get round the Carrier constraint. Snakes, for example have only one lung.^[2] And, of course, dinosaurs were bipedal to start with, and most groups stayed bipedal to the end. Lizards run in short bursts with brief pauses. Carrier was able to show that they breathed in the pauses.^[1]

References

1. Carrier D.R. 1987. "The evolution of locomotor stamina in tetrapods: circumventing a mechanical constraint". Paleobiology (13): 326–341.
2. Cowen, Richard (15 December 1996). "Locomotion and respiration in aquatic air-breathing vertebrates". In Jablonski, David '; et al. (eds.). Evolutionary paleobiology. Chicago: University of Chicago Press. p. 337+. ISBN 0-226-38911-1.
3. Cowen, Richard 2003. "Respiration, metabolism, and locomotion". Richard Cowen, University of California, Davis. Archived from the original on October 21, 2014. Retrieved October 21, 2014. If the animal is walking, it may be able to breathe between steps, but sprawling vertebrates cannot run and breathe at the same time. I shall call this problem Carrier's Constraint.
4. Shipman, Pat 2008. (2008). "Freed to fly again". American Scientist. 96 (1): 20. doi:10.1511/2008.69.20. Archived from the original on March 4, 2016. Retrieved October 21, 2014. Carrier's constraint is named for David R. Carrier at the University of Utah in Salt Lake City, who observed that the typical sprawling gait of a lizard restricts the animal's ability to breathe while running or walking.