Why don't birds have teeth?

Why don't birds have teeth?

If you observe birds' feeding habits closely, you'll find that whether it's seeds, fruits, or insects, birds swallow them whole without chewing. Even a large fish is swallowed head-first, directly into the mouth, and then swallowed down the throat. For large foods that can't be swallowed, some birds, such as birds of prey, use their sharp claws and hooked beaks to tear them into small pieces before swallowing them one by one. Why don't birds chew their food? If we observe further, we'll find that birds don't have teeth at all in their mouths. Their mouths have a special name called the beak. The bird's beak is composed of an upper and lower jaw. The main part is a light, hard, and smooth bone, covered with a layer of softer keratin. Some birds, such as geese and ducks, have serrated or comb-like protrusions on the edges of their beaks, but these are made of a layer of keratin on the surface and are not real teeth. These keratin "teeth" help them eat aquatic plants or other foods. Even birds of prey like eagles don't have teeth in their mouths.

Since birds evolved from reptiles, and reptiles generally have teeth, why don't birds have teeth? Fossil evidence tells us that the earliest birds did indeed have complete teeth in both their upper and lower jaws, just like reptiles. But over time, these teeth gradually decreased and even disappeared, and the sharp-toothed reptiles' mouths evolved into the light, toothless beaks of birds. Why did this evolution occur, or what benefits did it bring to birds?

Firstly, without teeth, there's no need for a strong jaw or corresponding muscles, which helps reduce the weight of a bird's head and facilitate their flight. For example, the weight of a pigeon's skull accounts for only 0.2% of its body weight. Secondly, birds lead a flying lifestyle with high activity levels and rapid metabolism, requiring them to consume huge amounts of energy every day. To meet this demand, they must constantly search for food, swallow and digest it as quickly as possible, which makes it impossible for them to crush and digest food by chewing slowly like reptiles. Correspondingly, birds have evolved a special digestive system. Swallowed food is first stored in a well-developed crop, where it is softened and ground up before being digested and absorbed by other parts of the digestive system.