|
Agahnim -> RE: Microraptor: We have to admit it, folks (3/9/2008 1:34:24 AM)
|
quote:
Thanks for the kind words, Agahnim. [:)] I deeply appreciate them. You seem like a pretty awesome guy, yourself. You're on deviantArt, too?! Awesome! I'm Tyrannosaur17, if you want to look me up there (I'll be getting more artwork up there, I promise!).
Something makes me think I’ve looked at your art there before. Have you commented on any of my or my girlfriend’s submissions in the past? (My girlfriend’s account is http://ferahgo-the-assassin.deviantart.com/ .)
By the way, I hope you aren’t offended by my “Occam’s Razor” comic series. I don’t have anything against the few intelligent and reasonable creationists I’ve interacted with such as you, but as I mentioned before, I’ve found creationists like you to be exceedingly rare. At least 90% of the creationists I’ve known in my life fit the portrayal in my comics.
quote:
I just did some research on Archaeopteryx on Wikipedia, and found an interesting bit of info (if it proves correct). There's been a debate about which fingers develop to maturity (those which are manifested in the adult skeleton) during embryonic development in dinosaurs and birds. Birds' fingers develop from digits 2, 3 and 4 (if I remember the order correctly) while the three fingers found in most theropod dinosaurs seem to develop from digits 1, 2 and 3, though it's harder to tell in dinosaurs, since we can't exactly see every stage in embryonic development with a long-extinct animal.
It seems that Archaeopteryx has its digits growing from fingers 1, 2 and 3 (the same as dromaeosaurs and other theropods). That and a couple of other features lead me to revise my opinion and say that Archaeopteryx may well have been a feathered dinosaur and not a bird (if the Young-Earth account is true, that is). It's interesting that AiG, in their determination to not admit any feathered dinos, beats this fact to death about which fingers grow in the two animal groups, but they say Archaeopteryx is clearly a bird and leave this little tidbit out of their writings, at least to my knowledge.
You’re right that the wings of birds develop from digits 2, 3, and 4, while theropod dinosaurs seem to have lost their outer two digits. (4 and 5.) However, there’s a type of mutation that could have caused the genetic coding for digits 1, 2, and 3 in an animal to become copied to digits 2, 3, and 4, which has been observed causing similar changes in living animals. It’s known as a “frame shift”. One of the most famous examples of a frame shift mutation is the one that gave a bacterium the ability to digest nylon; perhaps you’ve heard of that example.
As you might expect, in a transition that’s documented only by fossils, it isn’t possible to find any direct evidence about whether and when a frame shift mutation took place. But since this is clearly something that happens, the fact that the transition between a theropod hand and a bird hand would have needed to involve a frame shift isn’t a reason to dismiss the idea of them being related, if other lines of evidence support it.
quote:
Agahnim, I would like to know if you can present any features indicating Archaeopteryx's state as a true bird. It is indeed an enigmatic animal, and I would love to get to the bottom of this. Really, I'm not that knowledgeable about animal anatomy, but I try to look at the features shared between dinosaurs and birds and point them out.
Although I could give you a list of features in Archaeopteryx that are associated with birds, (Talk.Origins lists a few of them here), the same problem with Linnaean taxonomy that I described in my essay at CF applies here also. Among maniraptoran dinosaurs and early birds, it’s almost impossible to identify certain features as “uniquely avian” or “uniquely dinosaurian”, because almost all traits normally associated with one group or another are found in animals from both of them. The bony chevrons you mentioned in the tail of dromaeosaurids is the only exception to this I can think of, since that’s a predatory adaptation which is completely specific to dromaeosauridae.
If you look at the Talk.Origins article, you’ll notice that the only feature of Archaeopteryx listed as completely unique to birds is the opposable hallux, but this part of the article might be out of date—Microraptor gui is widely considered to have an opposable hallux also. Even Archaeopteryx’s asymmetrical primary feathers, which are an aerodynamic feature that’s specific to powered flight in birds, are also found in Microraptor gui.
But there isn’t any sort of clear line separating Archaeopteryx from later birds, either. This diagram shows a comparison between the hands of two birdlike dinosaurs, Archaeopteryx, a slightly less primitive bird called Confuciusornis, an extinct flightless bird called a phorusrhacoid, and two modern birds. Robert Bakker has a similar illustration I’ve uploaded here which includes the hand of the Hoatzin, arguably the most anatomically primitive bird alive today, which as a chick has a pair of Archaeopteryx-like claws on its hands that it uses for climbing. It also has the same swivel joint in its wrist that’s found in Deinonychus and Archaeopteryx, albeit fairly modified at this point.
Although I often hear Archaeopteryx described as having a “mosaic” of avian and dinosaurian features, I think a better way to describe it is as representing the midpoint between the features associated with dinosaurs and those associated with birds, for those few features that can be associated specifically with one group or the other. Its shoulder joint is a good example of this. Although I mentioned it having the same type of shoulder joint that theropod dinosaurs have, I was simplifying slightly. You can see in this diagram that in theropods such as Syntarsus, the muscle to lift the arms pulls straight in one direction, whereas in Archaeopteryx it has a slight pulley-like setup. The pulley system becomes more developed in more advanced birds such as Confuciusornis, although I wasn’t able to find a picture of it in that animal, until it reaches the state that exists in modern birds.
Man, I wish this forum would let me include images in my posts.
quote:
I have an idea about the similarities in the two animals being explained in a Young-Earth paradigm, but I'll have to post it tomorrow to sufficiently develop it (time constraints, and what have you). Thanks for your time. My response will be finished soon.
I’ll be interested to see it. But remember, the most important question that needs to be answered is why in some cases animals with these similarities are related to one another, while in other cases God would have made it appear exactly the same way even though they aren’t.
|
|
|
|