mantooth02
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Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 12, 2009 14:08:27 GMT
This debate has come up in the recent theropod poll, entirely my own fault for that. What does everyone here think? I assume most people believe that birds evolved from dinosaurs but aren't dinosaurs themselves. This doesn't really make sense to me, humans haven't stopped being primates just because of a few million years of evolution. What do you guys think? Allow me to draw your attention to a poll conducted by Jeff Poling titled "Is it true that birds are "obviously" not dinosaurs?" It's an interesting and somewhat eye opening read. www.dinosauria.com/jdp/archie/poll.htm
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Post by schnautzr on Sept 12, 2009 14:48:57 GMT
Look at it this way:
Dinosaurs evolved from fish. Are dinosaur fish? Fish evolved from single-celled eukaryotes. Are dinosaurs single-celled? Single-celled eukaryotes evolved from archaea. Are dinosaurs archaea?
The reason humans are primates is because they meet all the requirements to be placed in that group. Taxonomy isn't about grouping creatures by their relation to other animals, it's about grouping them by their similarity to other animals. We do DNA tests to tell if something is a new species, and if there's enough of a gap, it's a new genus. If there's a more significant physical or behavioral difference, we go further and place them in a new higher level taxon, like a new order or family, sometimes even class (but that's very rare). Birds, mammals, reptiles, and amphibians are all very similar and technically would all belong to any of the several the fish classes if we use cladology.
At some point, the dinosaurs evolved enough that they were more avian than reptilian. That's when that particular divergent exited Theropoda and move on to Aves. Scientists haven't agreed yet where that point was for many divergencies, and you can probably guess why.
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mantooth02
Researcher
Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 12, 2009 15:13:38 GMT
Look at it this way: Dinosaurs evolved from fish. Are dinosaur fish? Fish evolved from single-celled eukaryotes. Are dinosaurs single-celled? Single-celled eukaryotes evolved from archaea. Are dinosaurs archaea? I don't think I need to tell you that the differences between birds and dinosaurs are significantly fewer than the differences between dinosaurs and single celled eukaryotes. I'm a bit insulted that you would go there with this. As for fish however, some scientists would argue that all tetrapods are technically sarcopterygian (lobe finned) fishes. Read " Fishes: A Slippery Subject" . Then I guess my question is to you what makes birds so significantly different from dinosaurs that they should be in an entirely separate class? What happened to them that they should be excluded from dinosauria which contain animals as different from each other as eoraptor, velociraptor, triceratops and stegosaurus? They don't lack or posses any major characteristic that is not shared with their ancestors except for perhaps flight. You cannot argue warm bloodedness as that is a feature likely shared with the majority of dinosaurs. You cannot argue feathers or body coverings as even ornithischians and pterosaurs have a body covering which shows it may have been a feature shared it their common ancestors. What is your argument? Whatever it is, most paleontologists don't acknowledge it as significant enough to make a difference.
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Post by schnautzr on Sept 12, 2009 16:50:42 GMT
Actually, whether dinosaurs are indeed sauropsidan reptiles has long been the subject of debate as well. If you ask me, warm-blooded dinosaurs are synapsid reptiles, not sauropsidan reptiles, but I'm not about to write a paper on that. I'll just deal with it until I do.
Birds are coated in flesh, not scales. I've heard of a bird covered in scales. Yes, the legs are scaly, but not the entire body. If you ask me, anything covered in scales is not a bird, and anything fleshy is not a dinosaur. The fish classes and Sauropsida are the only tetrapodal classes covered in scales instead of flesh. And ever since the revision of the word "reptile", it's gone without question that most dinosaurs are reptiles.
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mantooth02
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Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 12, 2009 19:12:50 GMT
Actually, whether dinosaurs are indeed sauropsidan reptiles has long been the subject of debate as well. If you ask me, warm-blooded dinosaurs are synapsid reptiles, not sauropsidan reptiles, but I'm not about to write a paper on that. I'll just deal with it until I do. Birds are coated in flesh, not scales. I've heard of a bird covered in scales. Yes, the legs are scaly, but not the entire body. If you ask me, anything covered in scales is not a bird, and anything fleshy is not a dinosaur. The fish classes and Sauropsida are the only tetrapodal classes covered in scales instead of flesh. And ever since the revision of the word "reptile", it's gone without question that most dinosaurs are reptiles. I don't know enough on the subject of dinosaur skin but umm...feathered dinosaurs do exist, are you saying under those feathers were scales and not skin? Also, feathers themselves are modified scales and scales themselves rest on top of skin. So are you saying feathered dinosaurs had feathers on top of scales on top of skin?
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Post by schnautzr on Sept 12, 2009 20:02:08 GMT
As best I understand it, yes. I have not seen any evidence of non-scaled dinosaurs, although at some point there was obviously a change, otherwise we wouldn't have birds. That's where the gray area would fall using my reasoning. Several (at least 3 or 4) dinosaur mummies have been uncovered. Particularly, Dakota. Dakota displays scales. Here's a news release from March last year: news.nationalgeographic.com/news/2008/03/080318-AP-dinosaur-mu.html
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mantooth02
Researcher
Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 12, 2009 21:52:00 GMT
As best I understand it, yes. I have not seen any evidence of non-scaled dinosaurs, although at some point there was obviously a change, otherwise we wouldn't have birds. That's where the gray area would fall using my reasoning. Several (at least 3 or 4) dinosaur mummies have been uncovered. Particularly, Dakota. Dakota displays scales. Here's a news release from March last year: news.nationalgeographic.com/news/2008/03/080318-AP-dinosaur-mu.htmlI realize there are dinosaurs with scales though they are quite different from those in lizards and snakes. I'm talking about animals like microraptor and archeopteryx, do you have any evidence that they had scales under their feathers? I doubt they did.
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Post by schnautzr on Sept 12, 2009 22:06:09 GMT
You're correct there. Also, what about beaks? All avians that scientists agree are avians have beaks. Many scientists will argue that a few with beaks weren't birds, or that a few without beaks are, but every specimen that all scientists DO agree on has a beak. Surely beaks and scaleless skin didn't happen at the same time. I'll have to do some research later, but I think this gray area of divergence from reptile to avian falls within Avialae.
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mantooth02
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Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 12, 2009 22:31:22 GMT
You're correct there. Also, what about beaks? All avians that scientists agree are avians have beaks. Many scientists will argue that a few with beaks weren't birds, or that a few without beaks are, but every specimen that all scientists DO agree on has a beak. Surely beaks and scaleless skin didn't happen at the same time. I'll have to do some research later, but I think this gray area of divergence from reptile to avian falls within Avialae. These questions would not need answering if birds were obviously not dinosaurs. There are many extinct birds with teeth. Archeopteryx has teeth and is classified as a bird. Hesperornis is another. There are also dinosaurs with beaks, such as oviraptor and other archosaurs as well such as pterosaurs. The lack of or presence of a beak does not define a bird and beaks are well known among various archosaurs. As for scaleless skin, I suspect feathered dinosaurs shared this feature with birds. Dinosaurs weren't skinless, their skin was under their scales. It only makes sense IMO that feathered dinosaurs like birds would have no need for scales where their feathers were. As for which came first, beaks or feathers. Feathers came first and thus I suspect scaleless skin came before beaks as well. Some scientists suspect feathers or feather like structures existed even before the dinosaurs in basal archosaurs and that the scutes possessed by dinosaurs evolved from them and not the other way around. There is an article about it, I'll have to see if I can find it. It sort of makes sense since both orders of dinosaurs along with pterosaurs all are known to have had a body covering in at least some species. Who knows, maybe body coverings were the norm in dinosaurs. Also the chemical makeup of scutes (dinosaur, bird and crocodile scales) are very similar to that of feathers but the scales of other reptiles are quite different in their makeup from feathers.
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Post by schnautzr on Sept 13, 2009 0:09:30 GMT
I may need to refresh myself on birds...I was thinking the beaks usually had teeth, especially in the case of ducks and other waterfowl. I won't say teeth make something a reptile or bird for that reason. I believe you're suggesting (and if you're not, I am) that feathers must be a highly specialized series of genetic mutations of scales, meaning that they replaced scales entirely rather than covering scales. Having arrived at this argument, I would venture to guess that the "hard feather-shaped structures" found recently on certain specimens must be the sort of scale-feather that existed during this series of mutations. It certainly makes sense to me that scales must become larger and then lighter but more durable during this process. A feather is less likely to break than a scale during a gliding process, so the survival of those reptiles (or birds) which had more featherlike scales led to the further development of feathers as we know them. Correct me if I'm wrong about the following: | Reptiles (sauropsidans and synapsids) | Birds | Warm-blooded | sometimes | yes | Beak | sometimes | yes | Teeth | yes | sometimes | Bipedal | sometimes | yes | Wings | sometimes | yes | Clawless pectoral wings | no | almost always | Handless pectoral wings | no | yes | Scaleless except hind legs | sometimes | yes | Feathered | sometimes | yes | Stunted lumbar vertebral column | no | yes |
Edit: Lol...asked my dad. Here's his response: "Birds are warm-blooded and have feathers." "What about Archaeopteryx" "What's that?" "Basically a lizard with wings that could fly" "I dunno; it's extinct so all that matters is the warm-bloodedness and feathers."
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mantooth02
Researcher
Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 13, 2009 1:11:08 GMT
The chart appears mostly correct but in looking at what makes a bird it's necessary to look at all birds beginning with the first animal classified as one. If archeopteryx is a bird than features like clawed hands, teeth and a beakless mouth can all be changed to "sometimes". No living birds have teeth. What ducks have are called lamellae and are just projections on the beak. Birds that did have teeth had them set in sockets, a characteristic of all archosaurs. When considering the origin of feathers it is important to remember that they didn't initially evolve for flight. Many dinosaurs had proto-feathers that were useless for flight but great for insulation, protection and display. I found that article I mentioned before, you might be interested in it. It's fairly old, before all of the recent feathered dinosaur discoveries. It seems to have been written in the late 90's at about the time Sinosauropteryx was discovered. It also suggests feathers evolved into scutes but it could be the other way around, scutes evolving into feathers. Feathers, scutes and the origin of birds www.dinosauria.com/jdp/archie/scutes.htm
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Post by schnautzr on Sept 13, 2009 1:47:13 GMT
I'll certainly give it a look. I think it is important now that we do clarify what one another sees as a bird. So far, the following tetrapods have been mentioned. Let me know which ones you feel are a bird or a reptile. (I left out Stegosaurus, Triceratops, and Centrosaurus, assuming you would not dare call those birds...) Archaeopteryx | reptile | | Sinosauropteryx | reptile | | Hesperornis | reptile | | Anas | bird | | Gallus | bird | | Compsognathus | reptile | | Hadrosaurus | reptile | | Oviraptor | reptile | | Eoraptor | reptile | | Velociraptor | reptile | |
I feel it's important to add a few others which are borderlined; feel free to add any you feel appropriate. Moa | bird | | Apteryx | bird | | Casuarius | bird | | Dinornis | bird | | Wellnhoferia | reptile | | Confuciusornis | bird | | Ichthyornis | reptile | |
By the way...I just noticed earlier you said you were insulted by my comment about fish...sorry if you found that insulting. I was using it merely to make a point that your initial reasoning wasn't quite solid. Confuciusornis was the most difficult for me to define, since it had hands. However, the avian characteristics outweighed the reptilian.
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mantooth02
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Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 13, 2009 2:20:32 GMT
Forced to decide I would consider Wellnhoferia, Archaeopteryx and Hesperornis all birds because they have one characteristic that they don't share with any of the other animals on that list, the ability to fly. Truthfully I look at birds as living dinosaurs and thus as reptiles so I personally don't need to make a decision. This is why the terms "avian dinosaurs" and "non-avian dinosaurs" exist because it is nearly impossible for scientists to come to a conclusion, the line on what is or isn't a bird is blurred. There are birds some argue are dinosaurs and dinosaurs some argue are birds. Surely if velociraptor could fly it would be classified as a bird, if flight is what makes birds what they are than that characteristic alone is not enough for them to qualify as non-dinosaurs and thus non-reptiles. Bats can fly but are still mammals. Birds can fly but are still theropods. I have no problem excepting birds as reptiles or as dinosaurs, in fact I like it, I think it's awesome that dinosaurs are still alive. Our current system of classification is flawed. After all, the closest living relatives of birds are crocodilians. Crocodilians are actually more closely related to birds than they are turtles, yet birds are given their own class and crocodilians and turtles share one. It makes no sense.
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Post by schnautzr on Sept 13, 2009 2:30:53 GMT
So what you're suggesting is that ratites, penguins, and other flightless birds are actually synapsids. I'm assuming you didn't consider the non-ratites, and I can see where one might consider a ratite such as Casuarius or Apteryx a reptile, although personally I consider them birds with wings incapable of flight.
You're right, the topic isn't relevant to life, so a decision does not need to be made. However, I enjoy discovering other people's views and learning their reasoning. It helps me realize my own reasoning.
From this conversation, I've discovered that from now on, when I say bird, it is a warm-blooded tetrapod that has feathers, wings, a stunted lumbar vertebral column, and a beak. Before today it was a rather blurry description.
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mantooth02
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Dieter the Saurornitholestes [F4:ManTooth02]
Posts: 134
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Post by mantooth02 on Sept 13, 2009 2:39:13 GMT
So what you're suggesting is that ratites, penguins, and other flightless birds are actually synapsids. I'm assuming you didn't consider the non-ratites, and I can see where one might consider a ratite such as Casuarius or Apteryx a reptile, although personally I consider them birds with wings incapable of flight. No, I don't consider birds to be synapsids. Mammals are the only living synapsids. Birds and all other reptiles are Sauropsids. because ratites and other flightless birds are secondarily flightless, having evolved from a flying answer they are in fact birds. They are birds with wing incapable of flight like you say. That's not what I'm saying. I'm saying that for me personally I know how I view birds. There is no question in my mind that birds are dinosaurs and since dinosaurs are reptiles so are all birds. I'm just trying to help you determine how you see them in your mind, trying to find out what makes birds non-dinosaurs in your opinion and help you get an idea of what exactly a bird is.
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