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Common leopard gecko. Carrier's constraint is the observation that air-breathing vertebrates with two lungs that flex their bodies sideways during locomotion find it difficult to move and breathe at the same time, because 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.
In contrast, the lungs of lungfish are subdivided into numerous smaller air sacs, maximizing the surface area available for gas exchange. Most extant lungfish species have two lungs, with the exception of the Australian lungfish, which has only one. The lungs of lungfish are homologous to the lungs of tetrapods.
A number of invertebrates have lung-like structures that serve a similar respiratory purpose to true vertebrate lungs, but are not evolutionarily related and only arise out of convergent evolution. Some arachnids , such as spiders and scorpions , have structures called book lungs used for atmospheric gas exchange.
It is only in the middle of the lungs that the blood and air flow to the alveoli are ideally matched. At altitude, this variation in the ventilation/perfusion ratio of alveoli from the tops of the lungs to the bottoms is eliminated, with all the alveoli perfused and ventilated in more or less the physiologically ideal manner.
Pulmonata or pulmonates is an informal group (previously an order, and before that, a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includes many land and freshwater families, and several marine families.
Apatosaurus must therefore have had either a system unknown in the modern world or one like birds', with multiple air sacs and a flow-through lung. Furthermore, an avian system would only need a lung volume of about 600 liters while a mammalian one would have required about 2,950 liters, which would exceed the estimated 1,700 liters of space ...
Unlike the more common gill-bearing aquatic animals, these air-breathing animals have lungs (which are homologous to the swim bladders in bony fish) and need to surface periodically to change breaths, but their ranges are not restricted by oxygen saturation in water, although salinity changes can still affect their physiology to an extent.
They are neotenic, although the larval gills are small and functionless at first, and only adults have fully developed (but inefficient) gills. They are obligate air-breathers with well developed lungs. [6] Proving they likely evolved from a terrestrial ancestor with an aquatic larval stage. Like amphiumas, they are able to cross land on rainy ...