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Natural Science Forum / Biology / Paleontology / July 2005Reptiles to Birds
This topic has been covered many times before, but I want to get a final word, if not a balance of preponderances. Were birds descended from some form of dinosaur, possibly some type of meat eating theropods (saurischians), or maybe something else (possibly ornithchians), and if so, what were they? Or did birds branch off earlier from the stem reptiles, about the same time that the saurischians and ornithchians were diverging from each other, possibly in the Triassic or slightly later? Where did pro-avis come from? Is the evidence relatively unequivocal on this subject? > This topic has been covered many times before, but I want > to get a final word, if not a balance of preponderances. [quoted text clipped - 3 lines] > maybe something else (possibly ornithchians), and if so, > what were they? Birds are theropods. Nobody can identify the ancestral species by name (or any ancestral species of anything, for that matter), but it's a fairly good bet that their closest relatives are the dromaeosaurs and/or troodontids. > Or did birds branch off earlier from > the stem reptiles, about the same time that the > saurischians and ornithchians were diverging from each > other, possibly in the Triassic or slightly later? No, this is not a viable alternative. > Where did pro-avis come from? Pro-avis is an imaginary intermediate between "thecodonts" and birds. Since it's imaginary, it came from someone's fertile brain. If instead you mean Protoavis, that came from the fertile brain of Sankar Chatterjee. > Is the evidence relatively unequivocal on this subject? Yes, unless you talk to one of the three or four people who still refuse to believe it. That would be Larry Martin, Alan Feduccia, Storrs Olson, or John Ruben. > > ... > ... > Pro-avis is an imaginary intermediate between "thecodonts" and birds. > Since it's imaginary, it came from someone's fertile brain. If instead > you mean Protoavis, that came from the fertile brain of Sankar Chatterjee. Hmm. So you are saying that birds are descended from thecodonts. Well, thank you. x >>>... >> [quoted text clipped - 6 lines] > > Well, thank you. That is not what Dr. Harshman said. Birds are descended from theropods. Thecodont is an obsolete term for a number of pre dinosaur archosaurs. Birds are descended from some of those archosaurs since the dinosaurs that birds are descended from count those basal archosaurs as ancestors. Ken >>>... >> [quoted text clipped - 6 lines] > > Well, thank you. No, no, a thousand times no. "Thecodont" is just an obsolete term referring to any archosaur that isn't a dinosaur or crocodylotarsan. It's a wastebasket group, and saying that birds are descended from thecodonts means no more than saying that birds are archosaurs (which they are). Birds are maniraptoran theropod dinosaurs. > This topic has been covered many times before, but I want > to get a final word, if not a balance of preponderances. [quoted text clipped - 6 lines] > saurischians and ornithchians were diverging from each > other, possibly in the Triassic or slightly later? Without exception, every bird species now surviving is a descendant of the walking cuckoo, which no longer exists. But the dodo was just a mistake. > This topic has been covered many times before, but I want > to get a final word, if not a balance of preponderances. [quoted text clipped - 10 lines] > > Is the evidence relatively unequivocal on this subject? Don't all the 2 legged walking dinosaurs look like plucked chickens? T-rex, alloasauras, and some of the smaller ones like velociraptor. I think they all evolved as birds and are still with us. Some may have gone extinct. The vulture may be old T-rex. >>This topic has been covered many times before, but I want >>to get a final word, if not a balance of preponderances. [quoted text clipped - 15 lines] > I think they all evolved as birds and are still with us. Some may have gone > extinct. The vulture may be old T-rex. Now that's a highly Lamarckian (in the original sense) viewpoint. Vultures are T. rex. Chickadees are Diplodocus. Blue jays are Stegosaurus. No, I'm afraid that birds are all descended from a single species of theropod, somewhere in the vicinity of dromaeosaurs. All other theropods not ancestral to that particular species are extinct without descendants. That includes T. rex. I love this stuff. Here we go. The most recent findings really provide evidence that yes, birds descend from somewhere around Dromaeosaurids. For the Strange Creature that posted this thread, Dromaeossaurids are very specialized Maniraptors, who are very specialized Theropods. Maniraptors are very special in that their hands are quite different from most other Theropods, hence the name 'Mani' raptor. A special condition in the wrist causes the digits to be pointed back into the body, and also allows for fusion of some of the digits, which is present in all birds+ Check out the Hoatzin on Google. I mean sweet. It has a finger or two sometimes in it's younger stages, and then fuses them as an adult. Dromaeosaurs, check out Microraptor to see exactly what that entails I gotta go! ~albaradru > I love this stuff. Here we go. The most recent findings really > provide evidence that yes, birds descend from somewhere around [quoted text clipped - 4 lines] > 'Mani' raptor. A special condition in the wrist causes the digits to > be pointed back into the body, Well, it allows them to be *folded* that way. > and also allows for fusion of some of > the digits, which is present in all birds+ What condition allows for fusion? > Check out the Hoatzin on > Google. I mean sweet. It has a finger or two sometimes in it's [quoted text clipped - 5 lines] > > ~albaradru > > Maniraptors are very special in that their > > hands are quite different from most other Theropods, hence the name [quoted text clipped - 7 lines] > > What condition allows for fusion? IIRC, /we/ in the womb have fused digits, or webbed anyway, at an early stage. The cells die away and the fingers un-fuse from each other? So you'd just have to skip doing that part? However, human unfused digits are going to be low-functional - like wearing mittens all the time. A different design of wrist might allow the fused organ to be more useful. Have I misunderstood? > > > Maniraptors are very special in that their > > > hands are quite different from most other Theropods, hence the name [quoted text clipped - 11 lines] > stage. The cells die away and the fingers un-fuse from each other? So > you'd just have to skip doing that part? I assumed that albaradru was talking about fusion of the *bones* in the digits, a condition present in almost all living birds. > However, human unfused digits are going to be low-functional - like > wearing mittens all the time. A different design of wrist might allow > the fused organ to be more useful. "Useful" depends on the context. In the case of bone fusion in the wings of birds, it results in a wing that's more rigid. > Have I misunderstood? Could be, but then I might have as well. I love this stuff. Here we go. The most recent findings really provide evidence that yes, birds descend from somewhere around Dromaeosaurids. For the Strange Creature that posted this thread, Dromaeossaurids are very specialized Maniraptors, who are very specialized Theropods. Maniraptors are very special in that their hands are quite different from most other Theropods, hence the name 'Mani' raptor. A special condition in the wrist causes the digits to be pointed back into the body, and also allows for fusion of some of the digits, which is present in all birds+ Check out the Hoatzin on Google. I mean sweet. It has a finger or two sometimes in it's younger stages, and then fuses them as an adult. Dromaeosaurs, check out Microraptor to see exactly what that entails I gotta go! ~albaradru > Don't all the 2 legged walking dinosaurs look like plucked chickens? Surely the closest the actual fossil evidence can come, is chicken bones? Or, rather, mineral deposits in the shape of chicken bones? Of course, reasonable inferences can be made as to how much flesh used to be there on the bones that also used to be there, and so forth. Thus we reconstruct creatures that look like plucked chickens, but probably that's partly because we kind of expect them to look like plucked chickens. >>Don't all the 2 legged walking dinosaurs look like plucked chickens? > [quoted text clipped - 6 lines] > probably that's partly because we kind of expect them to look like > plucked chickens. And of course the evidence from China is that many of them looked like unplucked chickens. |
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