I was in smacked city, heading off to snowboard. Somehow I got into a conversation with my dad and younger sister about dinosaurs and reptiles. Then my dad dropped the bomb on me and told me that chickens and birds came from dinosaurs. That then confused me because birds don’t have teeth. Where did they go?
In: Biology
Yes, Birds are descended from dinosaurs who had teeth, but teeth and jaws became beaks. Birds lost their teeth because they lost the bone structure needed for chewing. Bones are heavy, and birds have sacrificed a lot of bone strength in order to be able to fly well. If a modern bird had teeth, it would break its jaw if it tried to crush or tear with them. Teeth have been replaced by a variety of specialized beaks, some of which are actually quite sturdy. Others use their beaks for reaching into things, and then swallow their prey whole, which they then crush using muscles in the crop.
Most birds are no longer hunting mammals or other animals that are larger than them, birds still have jagged edges inside their beaks if you look closely but they simply don’t need large meat cutting teeth anymore
Birds swallow their food whole and it is ground up by the gizzard, a muscular organ in their stomach, so they can digest it. They therefore don’t need teeth to chew so teeth would be a waste of resources.
Firstly, birds don’t come from dinosaurs, they *are* dinosaurs.
The current thinking as to why birds don’t have teeth is because it was a side effect of faster incubation. If you’re hanging around in an egg for a long time you’re vulnerable – you can’t move, your parents have to defend you. It’s not ideal.
So there would have been a decent amount of selection pressure in favour of genes that sped up incubation. It would seem that, as teeth take a long time to form, that these speedier incubation genes had the side effect of simply not activating the ‘teeth genes’ – the embryo never gets to the teeth growing stage.
The previous thinking was that birds lost teeth to enable flight, but this doesn’t explain why numerous non-avian dinosaurs lost their teeth and formed beaks too (eg Oviraptor, ‘egg-thief’, a good example of why you don’t want to hang around in eggs too long).
There’s a lot of the usual answers to this so far, and while some of them are in a way correct, they’re not exactly spot on. It is true that teeth are heavy, and birds undergo several strategies to reduce their weight (hollow bones, reduction of organs, reduction in the number of bones), it kind of flies in the face of the evidence of the crop. In short, teeth may be heavy, but stones are heavier. So why would a bird give up teeth to take on an organ that often houses material used for the same purpose that is even heavier? The answer is physics.
Simply put, birds that fly need to have their center of gravity around where their wings cross their body’s longitudinal axis (this is where the “lift” acts upon the body). If the center of gravity was behind this point, the “butt” of the bird would always be dragging, and if it was ahead of this point the bird would always be in a nose dive. In either case, flying would be severely difficult if not outright impossible. So if a bird had teeth (at the very front of the animal) this could shift the center of gravity ahead of the wings, and then the bird would be unable to fly. The crop is typically right at the point of where the wings cross the longitudinal axis (or very close to it) so the center of gravity is enhanced at the position of the wings, as well as below this point, which helps to add stability to flight. We see a dynamic example of this sort of “focus on the center of gravity” scenario with the pelican. We all know the pelican has that enlarged gullet for carrying food items. When the gullet is empty, we can see the head held somewhat erect with an upright neck while in flight (I don’t think I’ve ever seen a picture of a pelican with its neck stretched straight out like a goose in flight, perhaps because of the weight of its own skull), but when the gullet is carrying something, we always see the head tucked back overtop the body, trying to keep that center of gravity positioned with the wings.
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