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Acording to current scientific knowledge, birds descend from theropod dinosaurs. This evolution had, as usual, some transitional forms, like Archaeopteryx.

Following this evolutionary path, we notice that the birds lost their teeth in favor of a beak. But, from my research, it is not entirely known how birds lost their teeth. And even though some scientists mention that Archaeopteryx had a sort of beak, I don't think its skull is much diferent than, say a Velociraptor of sorts (that's my uninformed, layman opinion).

Archaeopteryx skull

For my world, I would like to have some kind of reverse evolution, where a bird of prey develops some dinosaur-like properties. I am not interested in detailing on my book the evolutionary pressures that would lead to this, so feel free to extrapolate acording to what will make your answers more plausible or easy to respond.

What I am interested in... is that this transitional form is fully functional (otherwise, it would go extinct) and that it would have a beak and teeth simultaneously (so as to illustrate where it came from and where it is going to).

As I said, the Archaeopteryx model doesn't seem to highlight the beak thing too much... I would lean more on the Triceratops model, but alas, that was a herbivore, not a carnivorous species (as I would like it to be).

Triceratops skull

So, my question is: how would this creature's skull be? Should I go with the Archaeopteryx model, since it has been tried and aparently been successful for some million years? Is there a way to have a carnivorous Triceratops model? Or could you guys figure out another alternative?

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Birds are dinosaurs, specifically they are maniraptoran coelurosaurs, more specifically eumaniraptorans--just like Velociraptor. For an indication of how the jaws of toothed birds would look like see Ichtyornis and Hesperornithes, true birds (Avialae) which lived in the Mesozoic and had functional teeth. (Modern birds have the genes for making teeth, they just don't express them.)

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    $\begingroup$ Ironically that train of thought helped me to solve the old question of "which came first, the chicken or the egg," and due to evolution, and crossbreeding of similar enough of stock, I came to the conclusion the egg(s) came first. $\endgroup$ – Jesse Cohoon Jan 3 '17 at 4:14
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    $\begingroup$ @JesseCohoon A simple way to think of it is that a chicken is genetically identical to the egg it hatches from but not to the egg it lays. Therefore for every chicken there is a preceding chicken egg, but for every non-chicken there need not be a resultant non-chicken egg. Therefore the first chicken egg precedes the first chicken. $\endgroup$ – ApproachingDarknessFish Feb 3 '17 at 18:20
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There are several oviraptoridae with teeth. Keep in mind birds don't chew they swallow and let the gizzard do the processing. The oviraptors have a few spiky teeth in addition to the beak. there are also Hypsilophodonts with a beak on the upper jaw and teeth on the lower in addition to chewing teeth.

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There is a dino-guy who's doing something along this line... well, specifically he wants to create a dinosaur from a chicken but thats not the point.

The genes to create teeth in birds still exists, it's just not turned on (in fact the dino-guy managed to create a bird embryo with teeth but due to ethics he had to terminate it). Therefore there would not necessarily be obvious 'transitional' forms as such. It could just be that a species of bird is born with teeth, and they're not harmful to the organism. That bird would then go onto reproduce, which would allow an entire population to be born with teeth. If the teeth become useful they they'll become widespread and permanent.

I'm not sure if this is useful or not but thats my knowledge on the situation.

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I would expect it to develop initially in fish-eating sea birds or waterfowl. Simple teeth are quite useful for holding on to slippery fish.

In fact, this has already happened. Ducks and geese do not have true teeth, but they do have serrated surfaces on their bills that serve the same function. And penguins do not have visible teeth on their beaks, but they do have them on their tongue. And the roof of their mouth. And the inside of their throat.

Most birds that would have a use for teeth find an alternative because teeth are heavy and flying is important for birds. But a flightless water bird that did not opt for the Sarlacc pit solution of the penguin's ancestors might plausibly revert to a dinosaur-like form.

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Some birds started to evolve teeth-like structures, check geese, toucans with saw-like beak extensions, and there is also a species of hummingbird with spikes on beak that looks like teeth.

Evolution never goes backward, so instead of growing their ancestor's teeth, birds could invent "teeth" again.

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  • $\begingroup$ Atavisms might be viewed as evolution "going backwards", depending on how they arise (eg. mutation knocking out a suppressor gene). $\endgroup$ – Starfish Prime May 26 at 18:39
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Some carnivorous birds already did this. It's most obvious in pelagornithids, also known as pseudotooth birds. In addition to being among the largest birds ever to fly, they had false teeth which were actually outgrowths of the jawbones.

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Raptors also have something similar, albeit in a much more subtle form. Tomial teeth are sharp little projections found in the beaks of birds of prey, and also a couple of other groups like shrikes and butcher birds. They assist in killing prey.

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Geese and their relatives have comb like structures in their mouths called pectens; these can be quite terrifying. In flamingoes, they have been modified into filter feeding organs, kind of like the baleen of mysticete cetaceans.

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Penguin mouths are quite horrifying, not least because of their awful tongues. Yes, their tongues are covered in large tooth-liked spikes, known as lingual papillae, which presumably help them munch fish.

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Speaking of papillae, a lot of birds also have these things called choanal papillae, which are backward facing spines which are found deep inside the mouth, around what's known as the choanal slit.

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I think that all of these qualify for your hypothetical transitional species with both a beak and teeth. As often happens with these questions, it seems that nature did it first.

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