From what I understand, birds evolvd from small dinosaurs that were probably already covered in feathers. But from (artists’ impressions) pictures of Archaeopteryx (one of the first “birds”, I believe), its head looked somewhat like a lizard’s, complete with teeth. So it’s somewhat easy to see why all birds have feathers (the first birds inherited feathers from their dinosaur ancestors). But it doesn’t appear that the first birds had beaks. While it’s easy to see why beaks might be advantageous for some, why didn’t some birds continue to evolve with some sort of different mouthparts? Maybe it has something to do with flight, but insects and bats seem to do fine without beaks.
So why did birds evolve beaks, and why do ALL birds have beaks now? Why haven’t ANY birds kept teeth?
I believe the standard explanation is that beaks are much lighter than regular jaws with teeth, thus making them hugely advantageous for flight. Since all birds have beaks, they most likely arose very early on in the evolution of flight.
This is just off the top of my head. I’m sure Colibri will be along shortly to offer a more authoritative explanation.
There were lots of toothed birds. It’s just that every lineage of toothed birds went extinct at the end of the Cretaceous, and only toothless birds survived.
The simplest explanation is that it was just random chance. Most species went extinct, and by chance some beaked bird species survived, and all modern birds evolved from those that survived.
I’m going to throw out a WAG here: When a bird flies, its mouth parts are the farthest forward part of it. If it were made of teeth and bone, it would take either a lot of effort or a counterweight to keep the bird from tipping over in flight. So it’s not so much the weight as it is the torque.
Darwin’s whole theory came about largely from watching Galapagos finches and how the beaks varied so significantly as they found unfilled niches and adapted to them. The beaks were one of the most variable aspect of the different species and its obvious that beaks could repurpose pretty quickly. Thus, you had birds eating insects, seeds, fruits, etc. with the proper beak for each purpose.
So the answer may be that simple - perhaps beaks are more easily adaptable than teeth. Thus, beaked birds would adapt more quickly to new niches than toothed birds. By filling more niches, they increase the odds that at least some survive an extinction… and they spread that much faster following the extinction. A less adaptable toothed bird would rarely find an unfilled niche and would have to really excel at its current one to survive.
Of course, that is mostly a WAG. The logic is sound enough, but we really don’t know.
Both correct, to a degree. The adaptive value in the ancestors of modern birds was probably that the loss of teeth made the skull much lighter. However, many successful lineages of birds in the Cretaceous had teeth. The fact that only beaked birds survived the end of the Cretaceous may have been a matter of chance. We don’t know whether the weight advantage on the part of beaked birds might have enabled them to outcompete toothed birds in the long run if the latter had survived the KT extinction event.
In any case, modern birds in some cases have evolved tooth-like modifications on the bill, such as falcons and other raptors, some pigeons, and some fish-eating ducks. The most extreme was probably the extinct Pelagornis.
You’re joking, but of course if mammals had beaks they wouldn’t be able to suckle. And there are two kinds of mammals - the platypus and the echidnas - that do have beaks. However, the young don’t suckle, because the females lack teats - instead they just lap up the secreted milk.
Mammals have adopted a different strategy, we’re the only group that has highly differentiated teeth. In the other vertebrate groups the teeth don’t vary much in shape, being for the most part just conical pegs. Additionally in each species the teeth tend to be uniform: all curved, or all rounded or all spikes etc. Look at the teeth of a crocodile or a fish, they vary in size but you can mostly replace any tooth with any other tooth just by scaling. There are a few exceptions to this rule of tooth uniformity, but even there the solution has often been fusion of teeth rather than true differentiation.
In mammals not only do different species having different teeth, but we have radically different types of teeth within the same jaw. The success of mammals depends in large part on the fact that we’ve evolved evolvability of our teeth. The other vertebrate lineages never seem to have evolved that evolvability, and so it wasn’t open for birds. As a result when birds needed adaptability they took another route, that of modifying the jaw and jaw covering.
The mammalian strategy is obviously superior since it allows a far greater diversity of food to be consumed. However the avian solution isn’t too bad.
Ok then, why (on dracoi’s reasoning), don’t fish or reptiles (all of them) have beaks, or why aren’t all mammals like platypuses?
The point is that no quite general advantage of beaks over teeth (as dracoi proposes) is going to work as an explanation, when all sorts of non-birds have teeth and not beaks.
I’m not sure that’s a serious objection. The dolphins have beaks for all intents and purposes, insofar as the narrow jaw protrudes from the front of the skull and effectively lacks lips so the young are incapable of sucking. Yet the dolphins still have teats and the young thrive despite that limitation. They get around the problem by squirting milk into the young’s mouth. The young swallow a bit of salt water, but not huge amounts. On land the mechanism would be even more efficient because the milk wouldn’t get diluted.
The need to suckle might explain why mammals evolved from animals without beaks, and it might explain why bird never developed lactation, but it can’t explain why mammals don’t have beaks, because a few mammals do have beaks and they get on with the suckling just fine.
I wouldn’t be too sure of that conclusion. For one thing, there are more different species of birds than species of mammals. For another, a lot of mammals have limited diets, and some birds are quite omnivorous. Crows, jays, and ravens, for example, not only eat a diverse range of food.
The fish are a different kettle of… well, fish. Most species are vacuum feeders, meaning they open their mouths and suck food in. That strategy is excellent in a dense medium like water, but obviously won’t work in air. Vacuum ingestion also obviously won’t work with a beak. Oddly enough the predatory fish that don’t feed via vacuum ingestion do mostly have beaks of some form. The herbivores don’t have beaks because beaks are a pretty lousy way of processing tough plant foods, which is one reason why so very few birds eat leaves.
Of the living reptiles, the turtles tend to be water dwellers and face the same problems as fish. The tortoises feed on tough plant material and while they have a horny “beak” of sorts you wouldn’t really call them beaked animals, indeed they have shorter rounder skulls than most species. The lizards generally feed on relatively large prey and need the crushing power of their jaws intact. Birds have secondarily evolved a way around this by developing tearing beaks, but there’s no obvious way for a reptile preying on large animals to evolve a beak directly, they need to pass through a phase of eating small prey first. The snakes lack limbs and feed on prey bigger than themselves, so it is impossible to have beaked snake. You could have a beaked monitor I guess, but the fact that such hasn’t evolved isn’t indicative of much.
As for why all mammals aren’t like the monotremes, it’s because we have a better, more adaptable feeding adaptation in our variable teeth.
I agree. My remark wasn’t intended to support dracoi’s statement, but rather to point out that the fact that mammals suckle may make the development of a beak more difficult.
I wasn’t intending it as a serious objection. There are a few mammals with beaks, and as you mention there are work-arounds so that young can be fed even if, as in whales, they don’t have cheeks.
Some have, of a sort. Pigeons feed their young with a “milk” produced in the crop, but of course don’t suckle.
Being speciose doesn’t tell you anything about the diversity of diet.
1)The most omnivorous mammals have far, far more diverse diet than the most omnivorous birds. Omvivores such as bandicoots, pigs and bears will eat pretty much anything, including bones and grass. Crows can not eat such foods because they lack teeth.
The dietary range of mammals as a group is far higher than that of birds as a group. While large numbers of mammals eat exactly the same foods as any bird, large numbers of mammals eat foods that are eaten by almost no birds. So, for example, large numbers of mammals eat bones, krill, tubers, grass, tree leaves etc. In contrast very few birds are capable of eating such foods and the few that do tend to be highly specialised (though there are a few geese and similar that graze).
A lack of teeth has forced specialisation on birds. So while a fox will happily prey on healthy animals as large as itself and still eat fruits and vegetables, fish and carrion, any bird that wants to eat prey as large as itself needs to have such specialised beak structure that consuming fruits and vegetables ceases to be an option. Similarly a squirrel or a rat can make a good living off acorns and grass seeds and remain effective predators. A bird that lives of grass seeds or acorns needs such specialised beak and digestive structures that predation creases to be any sort of option.
There can be no doubting the conclusion that mammalian teeth allow a greater diversity of food to be consumed. Mammals consume a greater diversity of foods. A greater proportion and diversity of species consume any given food type. Specialist mammals have a more diverse diet than specialist birds, omnivorous mammals have a more diverse diet than omnivorous birds.
I would attribute the greater diversity of birds than mammals to flight rather than diet. The second most diverse group of mammals (after rodents) is bats.
For the most part birds are incapable of subsisting on a diet made up mainly of leaves (as many mammals can). Leaves take more time to digest, and flying birds can’t afford to crate around all that extra weight while they are digesting. Birds generally require more high-energy food sources like insects, seeds, and fruit. (Of course there are some exceptions like geese.)
