[Mariana (OP)]

Claire asks:

Since birds are the evolutionary descendants of dinosaurs, why don't birds have teeth, and when did they lose them?

Do you know the answer?

[RD]

Since birds are the evolutionary descendants of dinosaurs, why don't birds have teeth ...

Some still do (atavism) but it's "as rare as hen's teeth" ...
https://www.sciencedirect.com/science/article/pii/S0960982206000649

[evan_au]

Some dinosaurs had beaks and no teeth, for example:
http://dino.wikia.com/wiki/Gallimimus

[Perorysa]

I know this reasonably But the advice from somebody anyway

[Petrochemicals]

I know this reasonably But the advice from somebody anyway

What does that mean ?

[Universal_learner]

Claire asks:

Since birds are the evolutionary descendants of dinosaurs, why don't birds have teeth, and when did they lose them?

As birds needed to fly, they needed to reduce their density, so it make sense it is a weigth reduction that made an adapatative advantage.

[OokieWonderslug]

It takes longer to grow a muzzle and teeth than it does to make a beak. Eggs that hatch earlier are much more likely to live and reproduce. So any birds that had teeth had fewer chicks. Kinda simple.

[Monox D. I-Fly]

Claire asks:

Since birds are the evolutionary descendants of dinosaurs, why don't birds have teeth, and when did they lose them?

As birds needed to fly, they needed to reduce their density, so it make sense it is a weigth reduction that made an adapatative advantage.

So... Do flightless birds not have teeth?

[evan_au]

A recently documented toothed bird, preserved in amber:
https://www.abc.net.au/news/science/2020-03-12/fossil-of-hummingbird-like-dinosaur-found-in-myanmar-amber/12033634

[Anad Rutner]

The scientific consensus is dinosaurs were reptiles: cold-blooded. 

Birds are warm-blooded.   Next?

[Kryptid]

The scientific consensus is dinosaurs were reptiles: cold-blooded. 

You might want to update your knowledge about dinosaurs a few decades.

[Bored chemist]

You might want to actually get your information from something other than comic books.

You might want to stop acting like the kind of kid who is still reading comic books.
https://en.wikipedia.org/wiki/Physiology_of_dinosaurs#What_the_debate_is_about