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Natural Science Forum / Biology / Paleontology / March 2006Fossil ruffles feather evolution theory
http://www.cnn.com/2006/TECH/science/03/15/unfeathered.dinosaur.ap/index.html Fossil ruffles feather evolution theory NEW YORK (AP) -- A 150 million-year-old fossil from southern Germany has paleontologists ruffled over how feathers arose in the line of dinosaurs that eventually produced birds. The fossil is a juvenile carnivorous dinosaur about 2 1/2 feet long that paleontologists have named Juravenator for the Jura mountains in southern Germany where it was found. It would have looked similar in life to the fleet-footed predators that menaced a young girl on the beach during the opening scene of "The Lost World," the second "Jurassic Park" movie. The fossil's exceptionally well-preserved bone structure clearly puts it among feathered kin on the dinosaur family tree. Because all of its close relatives are feathered, paleontologists would expect Juravenator to follow suit. But a small patch of skin on Juravenator's tail shows no sign of feathers. And the skin also doesn't have the follicles that are typical of feathered dinosaurs, said Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County. He and Ursula B. Gohlich of the University of Munich describe the fossil in Thursday's issue of the journal Nature. "It has a typical scaly dinosaurian skin," Chiappe said. The paleontologists believe Juravenator's closest known relative may have been a fully feathered dinosaur from China, Sinosauropterix. There are a number of possible explanations for Juravenator's nakedness. Feathers could have been lost on the evolutionary line leading to Juravenator after arising in an ancestor to both it and its feathered relatives. Or feathers could have evolved more than once in dinosaurs, cropping up in sister species at different times and places. It is also possible that this particular fossil of Juravenator, which appears to be a juvenile, only grew feathers as an adult or lost its feathers for part of the year. But there is another possibility as well, said Mark Norell, curator of paleontology at the American Museum of Natural History: It is entirely possible that Juravenator did have feathers, but they simply failed to fossilize. "Feathers are really just difficult things to preserve," Norell said. To support his hypothesis he pointed out that several fossils of the oldest known bird, archaeopteryx, lack feathers. Whether or not the new specimen raises interesting questions about how feathers -- and thus birds -- evolved, most experts do not see it as a challenge to the widely accepted view that modern birds are descended from dinosaurs. on Thu, 16 Mar 2006 01:42:11 GMT, rms <rsquires@flashremove.net> sez: ` http://www.cnn.com/2006/TECH/science/03/15/unfeathered.dinosaur.ap/index.html ` Fossil ruffles feather evolution theory ` NEW YORK (AP) -- A 150 million-year-old fossil from southern Germany has ` paleontologists ruffled over how feathers arose in the line of dinosaurs ` that eventually produced birds. ` The fossil is a juvenile carnivorous dinosaur about 2 1/2 feet long that ` paleontologists have named Juravenator for the Jura mountains in southern ` Germany where it was found. ` It would have looked similar in life to the fleet-footed predators that ` menaced a young girl on the beach during the opening scene of "The Lost ` World," the second "Jurassic Park" movie. ` The fossil's exceptionally well-preserved bone structure clearly puts it ` among feathered kin on the dinosaur family tree. Because all of its close ` relatives are feathered, paleontologists would expect Juravenator to follow ` suit. ` But a small patch of skin on Juravenator's tail shows no sign of feathers. ` And the skin also doesn't have the follicles that are typical of feathered ` dinosaurs, said Luis Chiappe, director of the Dinosaur Institute at the ` Natural History Museum of Los Angeles County. ` He and Ursula B. Gohlich of the University of Munich describe the fossil in ` Thursday's issue of the journal Nature. ` "It has a typical scaly dinosaurian skin," Chiappe said. ` The paleontologists believe Juravenator's closest known relative may have ` been a fully feathered dinosaur from China, Sinosauropterix. ` There are a number of possible explanations for Juravenator's nakedness. ` Feathers could have been lost on the evolutionary line leading to ` Juravenator after arising in an ancestor to both it and its feathered ` relatives. ` Or feathers could have evolved more than once in dinosaurs, cropping up in ` sister species at different times and places. It is also possible that this ` particular fossil of Juravenator, which appears to be a juvenile, only grew ` feathers as an adult or lost its feathers for part of the year. ` But there is another possibility as well, said Mark Norell, curator of ` paleontology at the American Museum of Natural History: It is entirely ` possible that Juravenator did have feathers, but they simply failed to ` fossilize. ` "Feathers are really just difficult things to preserve," Norell said. ` To support his hypothesis he pointed out that several fossils of the oldest ` known bird, archaeopteryx, lack feathers. ` Whether or not the new specimen raises interesting questions about how ` feathers -- and thus birds -- evolved, most experts do not see it as a ` challenge to the widely accepted view that modern birds are descended from ` dinosaurs. How about the possibility that feathers developed as a feature that could be switched on and off, like the colour of fur in arctic mammals - they were grown in winter, shed in summer; or more cleverly, were grown when the species moved into cold territory, and suppressed when they lived in a warm climate. A difficult trait to demonstrate, but also might be hard to discount... I wonder would that be a good solution for an animal that might have had limited internal thermoregulation...  Signature========================================================================== vincent@triumf[munge].ca Pete Vincent Disclaimer: all I know I learned from reading Usenet. > on Thu, 16 Mar 2006 01:42:11 GMT, rms > <rsquires@flashremove.net> sez: ` > http://www.cnn.com/2006/TECH/science/03/15/unfeathered.dinos > aur.ap/index.html <snip> > How about the possibility that feathers developed as a > feature that could be switched on and off, like the colour [quoted text clipped - 6 lines] > I wonder would that be a good solution for an animal that > might have had limited internal thermoregulation... Or feathers were just for sex display, or combat/competition like antlers and lions' manes, or only present in juveniles, like Bambi's spots, or a passing fad, or... I say, if fossils want to be understood more clearly, they should be make themselves more available. SignatureCheers, Gruebait "Real men don't click." >> on Thu, 16 Mar 2006 01:42:11 GMT, rms >> <rsquires@flashremove.net> sez: ` [quoted text clipped - 20 lines] > I say, if fossils want to be understood more clearly, they > should be make themselves more available. Feathers are unique structures in the animal kingdom. Feathers have two primary morphologic functions: Insolation, and flight. All modern birds that use feathers for sexual display do so as a secondary function, or else have evolved behaviors that use feathers originally intended for those primary functions for sexual display. Regardless, there is no doubt that the primary function of these unique structures was for insolation and/or flight. As such, it is highly unlikely that feathers would originate for sexual display as a primary function within any group of animals. George > >> on Thu, 16 Mar 2006 01:42:11 GMT, rms > >> <rsquires@flashremove.net> sez: ` [quoted text clipped - 35 lines] > flight. As such, it is highly unlikely that feathers would originate for > sexual display as a primary function within any group of animals. You got any evidence for this bald assertion? A downy coat of feathers may have originally been for insulation but it is highly unlikely that flight feathers developed directly from either scales or downy feathers. Look at the feathers on Archy's tail. They may have had some utility in flight but it also seems much more likely that it was primarily for display purposes. Some of the more recent feathered dinosaurs also had long feathers in places not useful for insulation or flight but common for sexual display. Ken >> >> on Thu, 16 Mar 2006 01:42:11 GMT, rms >> >> <rsquires@flashremove.net> sez: ` [quoted text clipped - 52 lines] > > Ken If you will re-read what I wrote, nowhere in my post did I say that flight feathers did or did not develop from either scales or downy feathers. I made no claim one way or the other in that regard. My claim was that there is no evidence that feathers for the purpose of sexual display evolved independently of their evolution for insolation or for flight. In other words, the evidence is that sexual plumage evolved from pre-existing feathers, regardless of the function of those original feathers. The reference to the use of horns and antlers in sexual displays fails to mention the fact that horns pre-date such usage. In other words, there is evidence that horns were originally used for defense, and that sexual display was a later adaptation. Even today, all horned/antlered animals use such appendages for both defense and sexual display. In fact, it can be argued that sexual display itself is a form of defense, and likely an offshoot behavior. As for the feathered dinosaurs, it is clear that the ones discovered to date are much younger, geologically speaking, than archeoptyrx, the oldest known bird. That indicates that feathers were evolving for quite a while before these younger feathered dinosaurs show up in the geologic record, giving them plenty of time to adapt feathers from some original purpose to that of sexual display. There had to be a reason for feathers to evolve in the first place, and I don't think sexual display fits that bill. Species in general evolve from more simple, generalized individuals to more complex, highly specialized individuals. Sexual plumage is a highly specialized trait in birds, as are antlers in mammals, and I see no reason to assume that that wasn't the case with dinosaurs, if they indeed had such plumage. George > >> >> on Thu, 16 Mar 2006 01:42:11 GMT, rms > >> >> <rsquires@flashremove.net> sez: ` [quoted text clipped - 39 lines] > >> for > >> sexual display as a primary function within any group of animals. See here bald assertion^^^^^. > > You got any evidence for this bald assertion? A downy coat of feathers > > may have originally been for insulation but it is highly unlikely that [quoted text clipped - 16 lines] > words, the evidence is that sexual plumage evolved from pre-existing > feathers, regardless of the function of those original feathers. I did, you should try it. > The reference to the use of horns and antlers in sexual displays fails to > mention the fact that horns pre-date such usage. In other words, there is [quoted text clipped - 3 lines] > be argued that sexual display itself is a form of defense, and likely an > offshoot behavior. What reference to horns and antlers are you talking about? Certainly not in my post. Please erect your straw men elsewhere. > As for the feathered dinosaurs, it is clear that the ones discovered to > date are much younger, geologically speaking, than archeoptyrx, the oldest [quoted text clipped - 8 lines] > to assume that that wasn't the case with dinosaurs, if they indeed had such > plumage. What are you talking about? Evolution is not a progressive process. Also I didn't exclusively discuss the later feathered dinosaurs. I primarily mentioned Archaeopteryx. All the various arguments of why Archy's ancestors started to fly ignores a salient detail. How did those dinosaurs get the long feathers need to even start limited flight? A logical answer is that they were developed for sexual display. I can easily see Archy doing a mating dance not unlike those of various ground nesting birds of today. Ken >> >> >> on Thu, 16 Mar 2006 01:42:11 GMT, rms >> >> >> <rsquires@flashremove.net> sez: ` [quoted text clipped - 45 lines] > > See here bald assertion^^^^^. Umm, Ken. Do you have evidence that any group of animals evolved feathers for sexual display only, and before feathers evolved for any other purpose? <snip> >> The reference to the use of horns and antlers in sexual displays fails >> to [quoted text clipped - 9 lines] > What reference to horns and antlers are you talking about? Certainly > not in my post. Please erect your straw men elsewhere. So, you are telling me that you jumped into this discussion having only read my post and no others? Try going back and reading all the post so you will know what is being discussed here. >> As for the feathered dinosaurs, it is clear that the ones discovered to >> date are much younger, geologically speaking, than archeoptyrx, the [quoted text clipped - 17 lines] > > What are you talking about? Evolution is not a progressive process. Says who? It certainly has bneen shown time and time again in the fossil record that groups of animals start out with very simply forms and gradually over time become more diverse, and more complex. Take a look at crinoids, for instance. They started out in the pre-cambrian as soft-bodied, structually simple animals. As one progresses through the geologic column, these animals become progressively more complex and advanced, and by the time we see their heyday in the middle Mississippian, they are among the most complex, and specialized hard-bodied sessile organisms around. Similarly with humans. You cannot tell me that you don't recognize that modern humans are more advanced that Neanderthals, or Homo Erectus, or Australopithicus. Evolution is change over time. It isn't always positively progressive, but it is almost always progressive. There are exceptions, of course (such as with horseshoe crabs). > Also I didn't exclusively discuss the later feathered dinosaurs. I > primarily mentioned Archaeopteryx. [quoted text clipped - 3 lines] > need to even start limited flight? A logical answer is that they were > developed for sexual display. Why is that a logical answer? Why not grown horns, or larger dorsal fins, or longer tongues? Feathers have a very complex structure. There is no logical reason (and certainly no paleontological evidence) to support the idea that feathers evolved originally so that polly could have sex. See below. I can easily see Archy doing a mating > dance not unlike those of various ground nesting birds of today. > > Ken I have no doubt that that is probably true, but like I said, sex generally doesn't occur in unless they can first 1) protect themselves from predation and the elements, and 3) acquire food. Most likely, feathers evolved in an arboreal animal (undoubtedly a dinosaur) in response to the need to flee predators and/or obtain food. Archy could well have been a decendant of one of those arboreal creatures. George >>>>>>>on Thu, 16 Mar 2006 01:42:11 GMT, rms >>>>>>><rsquires@flashremove.net> sez: ` [quoted text clipped - 48 lines] > Umm, Ken. Do you have evidence that any group of animals evolved feathers > for sexual display only, and before feathers evolved for any other purpose? It seems to me that both of you are very adamantly defending theories for which we have almost no data. We have three reasonable possibilities: feathers evolved for a) flight, b) thermoregulation, or c) display. I really can't see a rational way to choose among them. The earliest known feathered animal is Archaeopteryx, but it's obviously not the primitive condition. The animal with the likeliest approach to a primitive condition is Sinosauropteryx, but of course it had been evolving with its feathers for even longer than Archaeopteryx. You are both left with untestable evolutionary scenarios. By the way, the display function was suggested quite some time ago by the late Ned Johnson. [snip] > Says who? It certainly has bneen shown time and time again in the fossil > record that groups of animals start out with very simply forms and [quoted text clipped - 9 lines] > modern humans are more advanced that Neanderthals, or Homo Erectus, or > Australopithicus. As regards crinoids, you are correct as far as I can judge from my rather meagre knowledge of the critters, but I don't think modern humans are any more advanced than neanderthals, erectids, or australopithecines, except presumably in behaviour. Then we've got parasites, who tend to simplify as they specialize. >> Says who? It certainly has bneen shown time and time again in the >> fossil [quoted text clipped - 17 lines] > humans are any more advanced than neanderthals, erectids, or > australopithecines, except presumably in behaviour. We see a similar phenomenon with dinosaurs as well. They started out as small simple, generalized forms, and by the Cretaceous, had evolved into many highly specialized, usually large, often bizarre forms (Pachycephalosaurus, hadrosaurs, triceratops, protoceratops, etc). If you don't think that modern humans are more advanced than Neanderthals and Homo erectus, explain the modern phenomenon of civilization, and why the previous species never achieved it. > Then we've got parasites, who tend to simplify as they specialize. I have no idea what you are trying to say here. George >>> Says who? It certainly has bneen shown time and time again in the >>> fossil [quoted text clipped - 25 lines] > Homo erectus, explain the modern phenomenon of civilization, and why the > previous species never achieved it. It's a cultural thing. It most likely is not the result of enhanced abilities. >> Then we've got parasites, who tend to simplify as they specialize. > > I have no idea what you are trying to say here. > > George |
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