Because they are no longer needed. The ancestors of these animals, such as Archeopteryx, a mixture of bird and lizard that lived about 150 million years ago, had well-developed teeth. But, over time, the dentures lost their function and ceased to exist, giving way to the beak, which is an extension of the jaws, the bones responsible for moving the mouth. Like any evolutionary process, this radical transformation did not happen overnight and was only completed a few tens of millions of years ago, when the current birds appeared. Instead of crunching the food in their mouth, they swallow the entire meal. And how did they manage without teeth? The absence of chewing is compensated by a powerful digestive system, which has two stomachs: a chemical one – the proventriculus, which begins to dissolve food – and another mechanical one – the gizzard, which breaks down what’s left of the food (see illustration below). . Only after passing through this natural crusher does the food travel to the intestine and be absorbed.
