Despite the large amount of evidence that birds are the direct descendants of a group of theropod dinosaurs some researchers continue to protest the association, one of the most vocal opponents of the idea being Theagarten Lingham-Soliar. Working with Alan Feduccia and Xiaolin Wang (two other outspoken critics of the same topic), Lingham-Soliar published a paper last year proposing that the "protofeathers" on the fossil Sinosauropteryx were collagen fibers and not feathers at all. I didn't buy the hypothesis (see this summary for an excellent take-down) and the paper seems to have been largely ignored (Feduccia and others have been flogging the ideas that many of the feathers found on dinosaurs coming out of China or collagen fibers for years), but now Lingham-Soliar is back with a new paper on the controversial "bristles" on another dinosaur, although the popular media has once again managed to confuse this issue.
In a report just out in the Telegraph called "Bald Truth About Dinosaur Feathers," reporter Roger Highfield falls flat on his face when discussing Lingham-Soliar's new paper and the implications the research has for bird evolution. The piece opens with this lovely summary;
Prof Theagarten Lingham-Soliar at the University of KwaZulu Natal, claims today to have "refuted" a suggestion that primitive bristle-like structures that adorn the tail of Psittacosaurus are prototype feathers, as claimed by those seeking evidence to back the widely accepted idea of avian origins.
*Smacks head against wall.* For those of you unfamiliar with the details of this issue, Psittacosaurus was a Cretaceous ornithischian dinosaur that is grouped in the Infraorder Ceratopsia, better known as the "horned dinosaurs." Being that ornithischians are about as old as saurischian dinosaurs (the Order to which bird ancestors belong), one of the earliest known representatives being the 210 million-year-old Eocursor, Cretaceous ceratopsid dinosaurs are about as distant from the direct ancestors of birds as you can get and still be a dinosaur. Psittacosaurus has nothing at all to do with bird-origins, then, and I don't know anyone who has marshaled the existence of "bristles" or "filamentous integumentary structures" as evidence for bird origins among ornithischians. Indeed, the phylogenetic distance between Psittacosaurus and feathered theropods has made the presence of integuments on the ceratopsid controversial, so I am curious as to how Highfield came up with such an assertion as was printed.
The comments of Lingham-Soliar in the article further muddy the waters;
Scientists must really now choose - belief in the nebulous idea of protofeathers or the reality of collagen, the dominant protein in vertebrates.
I am convinced from the nonsense spouted by many of the people who denounce collagen in favour of protofeathers that they have never actually seen collagen in its natural or decomposing state.
Pretty cranky words, surely, but from what I have read researchers have primarily highlighted the differences between "protofeathers" and the potential "bristles" of Psittacosaurus. In the paper "Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus" by Mayr, et al., the scientists describe the structures found on the Psittacosaurus fossil to be integumentary structures that are not homologous to the structurally different "protofeathers" found on theropods. Even if Lingham-Soliar is right about the bristles on Psittacosaurus being collagen, then, this does not immediately mean that each instance in which feathers have been preserved is just another case of preserved collagen. Such a statement would be doing exactly what Lingham-Soliar is accusing other researchers of doing, and as many of you know he certainly has an agenda to put forward when it comes to feathers vs. collagen.
So what about the new paper itself? I may disagree with Lingham-Soliar about his characterization of the issues presented in the popular press and his other interpretations, but that doesn't mean that I should dismiss anything he produces out-of-hand. Surprisingly, the paper does not address specimen SMF R 4970 or the issue of "bristles" on Psittacosaurus directly, the main thrust of the paper being a comparison between the Psittacosaurus specimen MV53 from the Lower Cretaceous of Liaoning Province, China and the decaying skin of a great white shark (Carcharodon carcharias). While the paper describes the integumental structures of Psittacosaurus, the illustrations accompanying the paper are blurry and generally of a low quality; half the time I don't even know what I'm supposed to be looking at. For those of you wondering (as I did initially) why a shark was chosen for comparison, Lingham-Soliar reports that the fiber arrangement in the specimen seemed similar to that seen in sharks. The structures that Lingham-Soliar observed, then, seem to show that Psittacosaurus had thick, tough skin, presumably to help protect it from weather and predators. (As a side note, Lingham-Soliar says that the skin of the nurse shark is exceptionally thick as a defense against predation, but there is an important caveat to this. The skin of nurse shark females is much thicker than that of males as male bite the females during copulation, so skin thicknesses differ between the sexes in nurse sharks and seem to be an adaptation to mating behavior rather than strictly predation.)
Perhaps I'm missing something, but the new paper doesn't seem to say much of anything about the bristles found on specimen SMF R 4970, so Lingham-Soliar's statements in the Telegraph are especially bold. Admittedly I am not well-versed in the science of collagen and what happens to it during the course of taphonomic processes, but I see no reason why paleontologists should suddenly accept that any integumentary structure is just preserved collagen from the skin of the animal; the structures found on Psittacosaurus are still debatable and this paper doesn't do very much to resolve what they might be. Even the paper itself was not arranged or explained very well and the illustrations suffered from many of the same problems that plagued the Sinosauropteryx piece from last year, so hopefully a better description of the preservation of the soft tissues present in specimen MV53 will eventually be undertaken. I'm sure some creationists will jump on the popular reports as evidence that the dinosaur-bird relationship has crumbled, but given the content of the paper I'm not even sure it merited any popular media coverage at all.
[Hat-tip to Michael for bringing this to my attention.]
Lingham-Soliar, T. (2008) "A unique cross section through the skin of the dinosaur Psittacosaurus from China showing a complex fibre architecture." Proceedings of the Royal Society B, Published Online Tuesday, January 08, 2008
Mayr, G., et al. (2002) "Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus." Naturwissenschaften, Vol. (89), pp. 361-365
Osborn, H.F. (1923). "Two Lower Cretaceous Dinosaurs of Mongolia," American Museum Novitates, no. 95.
You took the words right out of my mouth: Lingham-Soliar does not address at all the issue of the "quills" of SMF R 4970 (for example, comparing widths of those elements to the collagen) AND no one has seriously discussed the proposed Psittacosaurus "quills" as homologous to feathers. So the popular reporting he is doing has practically nothing to do with the paper itself.
Now I don't even want to read this paper. Thanks for summarizing, Brian. Dr. Holtz is right--nobody has done an extensive study of Psittacosaurus' quills, and actually nothing has been written on them since the intial report (to my knowledge). I seriously doubt their homology to feathers. The quills seem to be just that--hollow, cyndrical structures with some amount of flexibility. Sure, feather quills are hollow and cyndrical, but you know what else is? Porcupine quills! Granted, porcupine quills are technically hairs, but you get the idea.
Great, but did you have to say "Infraorder" and "Order"? :-)
Also, Saurischia and Ornithischia are by definition sister-groups and therefore equally old. We just happen to know older saurischians than ornithischians at present.
BTW, the "Novitiates" are just Novitates.
nothing has been written on them since the intial report
This is unfortunately correct.
Interesting post. We do have a talent for conflating and confusing things.
Whereto Psittacosaurus Bristles
It could be a case of convergent evolution that didn't get that far. Any work on how the bristles arose? From what did they grow? How did they grow? Are any bristles known that show branching (as in feathers or of a different sort of branching)?
Then you have the ever popular question of how did the feature help the animal. Was there a difference in expression between male and female? Did the bristles make the animal look larger---thus less optimal as a meal---to a predator? Did the apparent larger size make a male appear more optimal as a sexual partner to a female?
A feature such as Psittacosaurine bristles doesn't persist unless either resources are so rich the feature presents no handicap to the animal, or it provides a benefit. Were resources so good the bristles were no real burden, or did they make a difference in survival? And what might they have evolved into had the ornithischian line continued?
Like some of the other commenter said, there haven't been any studies on the quills/bristles since their initial description, so many of those questions are still unanswered. Whatever they are, they're not homologous with the feathers on theropods like Sinosauropteryx, so they could have arisen for different reasons/from slightly different tissues. If you want to have a look at the Mayr paper I can send it to you.
If the quills were real they could have played a role in signaling, species/sex recognition, or even defense, but despite the controversy around them very little work has been done on them. If some more skeletons with the bristles came to light it'd definitely help determine answers to some of these questions, but for now the issue is largely enigmatic.
Did the bristles make the animal look larger---thus less optimal as a meal---to a predator?
Unlikely, because they are only on the tail.
And no, the quills don't branch. All others of your questions are good questions, but unanswered at present, and most of them are unanswerable as long as we only know bristles on this one specimen. :-(
Hum, let us say they ARE homologous to feathers, just for the sake of argument:
1. Saurischians had feathers/protofeathers.
2. Ornithischians had protofeathers.
3. The last common ancestor of both groups had protofeathers.
Since it is widely hypothesized that protofeathers evolved as a form of insulation for creatures with a ramped-up metabolism, doesn't this suggest that endothermy was primitive to dinosaurs? I suppose it could be secondarily lost in big critters likely to overheat, but it makes Bakker's stubborn insistance that all dinosaurs were endotherms seem a little less absurd, no? Of course if they ARE callogen fibers, (or elongate scales, etc) then forget it ;).
Well, they're NOT collagen fibers. Neither are the feathers on Sinosauropteryx. The scientists advocating that view clearly have an axe to grind. When I originally saw the psittacosaur quills, I originally thought them to be homologous to Stage 1 protofeathers (tubular shafts), just elongated ones. I now think that's unlikely, as there's a chasm of phylogeny between coelurosaurs and ceratopsians, and it would appear that protofeathers originated among coelurosaurs (although that view could change).
Endothermy among theropds is a near-certainty, sauropods maybe not so much, and improbable among at least ceratopsians (there's an excellent paper about that in Horns and Beaks.
David: The quills may well have been on other body parts as well, as there seems to be an uneven state of preservation on the quilled psittacosaur.
seem a little less absurd
It hasn't been absurd for a long time to insist that all ornithodirans were/are endothermic and homeothermic.
sauropods maybe not so much
Then what was the bird-type respiratory system good for? And how was the extremely fast growth possible?
and improbable among at least ceratopsians
Hard to imagine that they weren't endothermic, but I have the book and will read it.
The quills may well have been on other body parts as well, as there seems to be an uneven state of preservation on the quilled psittacosaur.
Possible. It does have scales in any case, though, which are also preserved on lizards and champsosaurs from the Jehol Group (and on a few other Psittacosaurus specimens from there), as well as on the occasional mammal tail, but not on theropods.
A nitpick, but ceratopsids are members of Ceratopsidae (which Psittacosaurus was not), when referring to members of Ceratopsia, use "ceratopsian".
I think that Feduccia and its collaborators are missing the point.
As D. Esker comment, if the structures from Psittacosaurus are homolog to proto-feathers, it only implies that proto-feathers are present in a common ancestor of Saurischia and Ornithischia (or even Archosauria, if they are homolog with Longisquama). If they are homoplastic, and even if Sinosauropteryx feathers are not homolog with bird feathers, it does not count as evidence against birds-as-dinosaurs, the same is for the 'problem' of finger homology.
Feduccia and the other researches need to provide an explicit cladistic analysis (i.e. with scored matrix) if they seriously want to show that bird are not dinosaurs.
How could that material be collagen? Collagen may look a bit like hair, but it is arranged more like clumps of wires or fiber-optic fibers than hair, and were they internal, the impression would most likely show them continuing down into the bone (like in the fossil of Corythosaurus). These bristles, however, not only seem to sit just on top of the bone (indicating it was a surface structure), but they also seem to "behave" like locks of hair.
Admittedly I am not well-versed in the science of collagen and what happens to it during the course of taphonomic processes, but I see no reason why paleontologists should suddenly accept that any integumentary structure is just preserved collagen from the skin of the animal; the structures found on Psittacosaurus are still debatable and this paper doesn't do very much to resolve what they might be.