Slashdot Mirror
How Birds Lost Their Teeth
An anonymous reader writes A research team from the University of California, Riverside and Montclair State University, New Jersey, have found that the lack of teeth in all living birds can be traced back to a common ancestor who lived about 116 million years ago. From the article: "To solve this puzzle, the researchers used a recently created genome database that catalogues the genetic history of nearly all living bird orders--48 species in total. They were looking for two specific types of genes: one responsible for dentin, the substance that (mostly) makes up teeth, and another for the enamel that protects them. Upon finding these genes, researchers then located the mutations that deactivate them, and combed the fossil record to figure out when those mutations developed. They concluded that the loss of teeth and the development of the beak was a two-stage process, though the steps basically happened simultaneously. The paper states: 'In the first stage, tooth loss and partial beak development began on the anterior portion of both the upper and lower jaws. The second stage involved concurrent progression of tooth loss and beak development from the anterior portion of both jaws to the back of the rostrum.'"
6005.99999 years ago, one of them flipped God the bird and so He did Smite them and lo their teeh were no more and there was lamentaion and suffering.
Also, beaks are much lighter than teeth, which was probably a significant factor.
Also also, if you're thinking about mammal teeth, you're probably imagining it wrong. One of the unique things about mammal teeth is their complexity relative to the other branches of the vertibrates. Studying mammal evolution has been described as an exercise in studying teeth.
It's thought this advanced tooth development went hand in hand with warm blooded development during the pre-mammal period as more adavanced, inerlocking teeth were requied to mash up food better for quicker digestion which was required for a faster metabolism.
Most reptile teeth look primitive by comparison. Except that simple teeth are easily replacable and so reptiles can regrow lost teeth much more easily (later on some mammals in the ungulates developed open roots for continuous growth which was useful for grazers, whereas others hae a large stock of teeth then starve to death when they run out). The specialisation makes these much harder.
It seems likely that birds did not have the great teeth for supporting warm blooded metabolisms, but rather the simple, robust general purpose teeth of other reptiles, so in this sense there were not losing nearly as much. They also solved the grinding problem in a different way, using a gizzard (this may well predate birds: crocs have gizzards as well and it is speculated that some dinosaurs did). As a result they were replacing the bit that grips and possibly does some initial cutting of food with a much more lightweight structure.
SJW n. One who posts facts.
The problem is you are not smart enough (no one is - except perhaps god) to understand all the intervening steps.
You don't 'give up' teeth, you get a mutation and are stuck with it. They are not making conscious decisions to evolve, that is just plain ignorance. If you can find a way to survive without the teeth, you continue on. Eventually you get another mutation, and maybe it evolves to take the place of something you lost.
Birds found a way to survive without teeth before they gained a beak. Possibly it was those rocks some birds swallow and use to grind up large chunks of food (I don't know when or if all do this).
Maybe teeth became a liability. People used to die from a rotten tooth, maybe there was an epidemic of bird tooth infecting microbes. It doesn't matter.
As for gender based on-single cell organism, you have that wrong also. Sex evolved from eating - the victim's genes survived inside the single cell that tried to eat it, and it's grew from there. At that point all those single celled life forms were hermaphrodite - they could eat or be eaten and their DNA would survive in the eater. Eventually, the hermaphroditic single celled life forms developed into two varieties - one that could eat and absorb the DNA (female) and the other that could be eaten and pass on their DNA (male).
Also there was no clear line between single celled life forms and multicelluar life forms. First came colonies that learned to cooperate but could also survive on their own.
excitingthingstodo.blogspot.com
The gizzard came first. I remember reading about dinosaur fossils found with small, smoothed stones where a gizzard would be. It seems likely that the saurian ancestors of birds already had gizzards. They had tearing teeth but no chewing teeth and depended on the gizzard to break down their food.
They have the loss of teeth and the development of the beak, but where did the gizzard develop? They would not have been able to loose their teeth and develop a beak without one, and birds are the only animal (That I know of) that has one.
Plus gizzards are great when fried. ;)
According to Wikipedia, many reptiles including dinosaurs have/had gizzards.
Apparently they were more successful than the ones with just teeth. That's all it takes.