(ORDO NEWS) — The adaptation of vertebrates to life on land has caused fundamental changes in the respiratory apparatus . Fish, pumping water through the gills, use the muscles located on the head and “neck” for this. So did the first land inhabitants: modern amphibians, including frogs, still bloat their throats, pumping air through their lungs. The real revolution began when the muscles of the thoracic region began to play this role, squeezing and spreading the ribs.
This significant transition is the subject of a new work by Robert Cieri of the University of Utah and his colleagues, whose article is published in the journal Scientific Reports . According to scientists, the transmission of lung ventilation to the muscles of the chest was associated with the adaptation of animals to movement on land on four legs.
The authors investigated the mechanics of walking in lizards, recording the movements of their ribs using the new XROMM method , combining X-ray video recording and computed tomography. This made it possible to obtain accurate three-dimensional models of moving chest bones for the monitor lizards and tag fixed on the treadmill. Visualization showed that when walking with the bends of the spine characteristic of reptiles in the horizontal plane, their ribs make an unremarkable but important movement.
Each rib rotates slightly relative to its vertebra. As a result, at each step of the lizard, its ribs on one side of the body are compressed, on the opposite – they are moved apart, and at the next step – vice versa. Without such a rotation, they would simply collide with each other. According to scientists, almost the same movements of the ribs are produced in reptiles and for breathing.
Perhaps, initially these movements arose in reptiles precisely to strengthen the body’s bends and accelerate running – and only then turned out to be incredibly useful for pulmonary respiration. Robert Sieri and his co-authors believe that the early tetrapods moved overland by bending movements, which led to an increase in the mobility of the vertebral costal joints. At some stage of development, the animals were able to move the ribs simultaneously on both sides of the body and regardless of walking, providing more efficient ventilation of the lungs.
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