It is always a pleasure when research succeeds in deconstructing the simple portraits of the evolution of living things that still dominate people’s minds. According to these schematic and incorrect views, it is as if organisms are always “in search of progress”; Every detail of anatomy and behavior would play a clear and specific role in the “struggle for survival”.
Balela. It’s much more complicated and interesting in the real world, as shown by a study by Brazilian researchers of inner ear structures without which no terrestrial vertebrate, including you, could run or roam around.
I am referring to the semicircular canals, and only those suffering from labyrinthitis can attest to the importance of their function. These three interconnected tubes, similar to bone donuts, house a fluid called endolymph and are attached to areas full of cells that act as sensors.
When a person or animal’s head moves, the fluid also moves within the semicircular channels, and cellular sensors detect changes and allow fine adjustments to be made to the body’s balance.
It makes sense that this system is very important for flying bugs that need to make quick changes in trajectory up and down for all sides – in addition to focusing the view during those complex movements. Hence the idea that the semicircular canals of birds would have been specifically designed to solve the hairy problems of balance in flight.
Mario Bronzati and his colleagues from USP in Ribeirão Preto and other institutions put this idea to the test in a study that has just been published in the current journal Current Biology. The judgment? It is better to forget this business that the canals of birds were created “for flight” simply because very similar things already existed in the skulls of some of the first dinosaurs, ancestors of birds (they are strictly speaking nothing more than two-legged and feathered dinosaurs that escaped mass extinction 66 million years ago).
In fact, the semicircular canals of birds are quite large, but the size of the structures in certain dinosaurs was comparable. The well-rounded shape that is typical of the canals in birds is not exclusive to them either and actually seems to be more related to the shape of the skull – rounder skulls “ask” about this design so that everything fits together without proper functional reasons.
Was it absolutely necessary to have large canals to fly? No, the pterosaurs, distant cousins of dinosaurs and birds, didn’t have them and still flew without the slightest problem. Apparently it was a much more general need – that of precise coordination between movements of the eyes, head, and neck during rapid movements – that was responsible for creating the pattern that remains in the feathered animals of today. Running, jumping from tree to tree or flying are equally important tasks for these structures.
One final irony: alligators and crocodiles – even more distant relatives of birds and dinosaurs, but still members of the same large group – have very different channels that were not necessarily the same shape in their distant ancestors. Rather than “getting stuck in the time of the dinosaurs,” these semi-aquatic animals have never stopped evolving. You and the rest of your life, of course.
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