Paleontology (Dinosaurs)/from dinosaurs to birds
Thanks for your reply! I have a few more questions which stem from your response.
You say that birds evolved from a group of theropods. Aren't theropods all lizard-hipped dinosaurs as opposed to bird-hipped? It seems like such an awkward transitional form from a heavy-tailed, small-armed scaled dinosaurs into a light, great-winged (a bird must have a reletively great wingspan if it is some kind of sea bird that flies a lot) feathered avian, especially if it had to change from lizard to bird-hipped. If evolution is a survival of the fittest, any animal in a transitional from such as that would not survive, correct? It be neither suited for the land nor suited for air.
Also, the proteins that make up a flight feather are extremely different than the proteins that make up a down feather, and since the proteins are coded by the DNA, then that means that the DNA must have changed, right? How could new information be added to create something new? I've seen plenty of instances where the DNA is lost, but to make a different kind of feather some different DNA codes must be added, and that'd be impossible, right?
If the surronding environment caused reptiles to change into birds, why didn't other animals also adapt to the environment? I know that there are many kinds of fossils in even the Cambrian layer that we still have living today. Why did the reptiles and other animals change but some animals still stay exactly the same, even though it is a supposedly much different environment today?
Sorry for all the questions but I really am very curious. Thanks for the time!
Being a creationist, I find your profile very interesting. I do not know much about the view of the supposed evolution of dinosaurs to birds (and I suppose that even there I'm rashly assuming that you hold that view), so I would just like to ask some fair and curious questions. If dinosaurs did evolve into birds, into what kind of birds did all the sauropods such as diplodocus evolve? Or T-Rex? Wouldn't it have made survival easier for the creatures anyway if they had stayed dinosaurs instead of evolving into birds? What kind of global conditions would have arisen that would have cause dinosaurs to have lived out "the survival of the fittest" by turning into birds?
Thank you very much for your time!
Hello there! Thank you very much for your interesting question - I am SO sorry that it has taken me so long to respond. I have been busy lately and haven't checked my email in about a week - not a very good excuse I know. Anyway on to your question.
Evolution does not work the way you seem to think. Any group of related animals has a single common ancestral species. Birds evolved from dinosaurs (and yes I hold that view - the evidence is overwhelming), but ultimately from only one species of dinosaur. By rigorous analysis of the skeletal features of the earliest birds (such as Archaeopteryx) we can pin down pretty closely the group of dinosaurs from which birds evolved. That group was part of the larger group known as theropods (think T-rex, Velociraptor etc. - the two-legged predators). Sauropods did NOT evolve into birds. And neither did most theropods - they either went extinct or gave rise to other theropods which went extinct or gave rise to other species ... and so on and so on, right up until 65 million years ago, at which point there were a) lots of ornithischian dinosaurs, b) lots of sauropods, c) lots of theropods that weren't birds (scientists call these non-avian theropods), and d) lots of theropods that WERE birds (having all been descended from the first bird, which was itself simply a feathered theropod that could fly). A lot of the non-avian theropods had feathers, as some very fine fossils from China have shown recently. It is possible that T-rex had feathers too.
Then came that great extinction event, which killed all of the ornithischians, all of the sauropods, all of the non-avian theropods, and MOST of the birds. It may have been pure luck that the only dinosaurs to make it through happened to have been birds, but I think it more likely that the flying habit of birds saved them. Perhaps the survivors were seabirds, which were still able to catch fish while the land-bound dinosaurs starved in the terrible conditions that followed the meteorite impact (or volcanic activity, or both, depending on which extinction hypothesis you subscribe to).
Feathers evolved for some purpose other than flight - possibly for insulation. Flight was a beneficial side-effect, and selective pressure for more efficient flight then steered feather evolution in a more flight-oriented direction. The earliest birds were not great fliers by modern standards - they lacked the keeled sternum which provides anchorage for the flight muscles in today's birds, they had long bony tails (like other theropods) and instead of beaks they had bony jaws with teeth (also like other theropods). In fact one skeleton of Archaeopteryx was mis-labeled for years as a non-avian theropod called Compsognathus for many years - the two animals were THAT similar (skeletally).
Evolution has no forward-thinking purpose, no 'goal', no conscious direction - it is not 'aware'. It is simply the process by which species adapt to suit their current conditions. If their conditions change over time, species will slowly change until they are different enough from their ancestors that we can say that they have evolved into new species. The change from dinosaurs to birds may seem huge now, but it was made up of lots of very small changes that took tens of millions of years to occur. During that time, each animal in that chain of descent was very nicely suited to its habitat - it would have to have been, otherwise it would have gone extinct.
So dinosaurs had absolutely no choice in whether they 'stayed' dinosaurs. By current scientific definitions, birds are in fact still dinosaurs, and will forever remain so no matter how different they become. Just as we remain primates and mammals.
I hope I have answered your question to your satisfaction, but I am more than happy to elaborate on anything you're still unclear about. Thanks again for your question!
Yes theropods were 'lizard-hipped'. But so were the first birds. The characteristic 'bird hip' evolved in birds later and merely involved the pubis gradually swinging backwards to lie alongside the ischium. That this also happened in bird-hipped dinosaurs is an example of convergent evolution.
In the transition from one species to another, or from one larger group to another, the transition is seamless. There is never an animal that is 'awkward' or that 'doesn't quite work'. You are right - such an animal would not survive. There ARE, however, plenty of animals that are less good at something (e.g. flying) than others. You seem to be demanding that ace-flying seabirds with huge wingspans descended immediately from non-flying dinosaurs. Well, it didn't happen that way! The first birds were poor fliers. That doesn't mean they weren't very good survivors. There are plenty of birds today which aren't very good fliers, yet can survive very well. It all depends on their lifestyle. A turkey is a terrible flier in comparison with a peregrine falcon, but who is to say which is the more successful species? In terms of numbers, it's the turkey.
The first birds are thought to have evolved on small islands in the central European archipelago. There weren't a lot of predators around, so they did not need to fly very well. They were scaly AND feathered, and yes they had long tails. BUT they had hollow bones (like many non-avian theropods), so they weren't all that heavy.
No, it's not impossible for DNA to be added. DNA segments can be added, lost, or replaced by means of copying errors. It happens all the time, and on occasion the resulting effects have a useful side-effect.
The environment does not dictate a single direction for change, and it does not dictate change for every animal. Each animal has to have a place, a niche, in the ecosystem. A change in the environment may be as subtle as a food plant developing thorns to protect itself from hungry herbivores - this may then lead to a particular species of hungry herbivore developing a longer tongue. The change that led to the evolution of flight in a certain species of feathered dinosaur may have simply been the improvement of flight in the insects that they fed on. This would not have affected crocodiles or sauropods in the least - they had their own challenges to face.
Some animals remain unchanged for long periods of geologic time, by virtue of their having settled into a niche that remains valid despite numerous large changes in other environments. You mentioned Cambrian animals - well there aren't exactly a lot of animals that have remained unchanged since the Cambrian, but one of them is possibly the little mollusc Neopilina, which is very similar to molluscs found in the Cambrian. It lives on the ocean floor at great depths - an environment that does indeed remain pretty stable.
All of this is pretty basic stuff. I suggest if you really want to get a handle on how evolution works, you pick up a book on the subject. And I don't mean one written by a creationist! :)