Blah blah feathered ornithischians yawn

Base of tail of Tianyulong (modified from Zheng et al., 2009).

Base of tail of Tianyulong (modified from Zheng et al., 2009).

Ok, I am actually really rather excited by this development but as ever I don’t want to go down the route of simply reviewing the paper as that is what I suspect every other blogger and news outlet is doing right now. For those who are already lost, today in Nature a new paper came out showing an ornithischian dinosaur – Tianyulong – with large integumentary structures (protofeathers is definitely pushing it at this point and is a term I’ll be avoiding with respect to this taxon at least for a long time to come) which superficially at least look very similar to those of theropod dinosaurs that certainly are precursors to feathers in birds. The big deal of course is that now we have these kinds of structures in both ornithischian dinosaurs and saurischian dinosaurs (the really fundamental split at the base of Dinosauria) and not just in saurischians. This opens up the possibility that these kinds of structures were ancestral to dinosaurs and thus inherited by both clades and did not just evolve in the derived theropods. However there is much more to this than meets the eye, most notably the fact that this is manifestly not the first ornithischian to have been suggested to have such structures.

I don’t want to belabour the details, I suspect the vast majority of my readers will have been inundated with this kind of information elsewhere and in far greater detail, so let’s rattle off the basics on this. If some of it does come as a surprise, do let me know!

1. This is a heterodontosaurid. These are now considered to be one of the most basal of ornithischians which fits nicely with the idea that this condition might be basal for dinosaurs and inherited in both major lineages.

2. Despite being Cretaceous in age (yes, it’s yet another Jehol taxon) this means the taxon itself was probably quite derived, but the lineage as a whole is basal (i.e. evolved early on – modern lizards are obviously derived animals, but in terms of reptiles, lizards as a whole evolved early on).

3. Ornithischians are incredibly rare in the Jehol fossil record so in some ways it’s not a surprise that these things have simply not been recoded before. Such soft tissues are incredibly rare and this is pretty much our only source for them, so coupled with a lack of ornithischians it’s not a surprise we had not found one sooner.

4. We cannot say for certain that these structures are homologous with protofeathers or similar structures in derived theropods (i.e. the same structure, modified in the same way). I would say they are almost certainly an example of parallelism however (i.e. the same original structure modified in a similar way), but until the distribution of these structures across Ornithischia and indeed in basal dinosaurs on both sides and their composition and distribution on individual taxa, I would not want to call them homologues, and certainly not protofeathers or feathers, though they clearly are similar and in a fairly closely related group.

5. Despite a general lack of such fossils with exceptional preservation I think it is problematic that all we have is just one definitive ornithischian with such covering and no evidence of such things in basal dinosaurs, dinosauromorphs, sauropods or basal theropods in the sense that “all / many / most dinosaurs had this”. It could still be that this is convergence, parallelism, or was present in basal ornithischians and then lost in later clades etc. Certainly it opens up that possibility, but it does not make it so, or, to my mind, even likely at this point.

6. Their distribution on the body, especially the elongate set on the base of the tail is especially interesting in the light of what we know of the other alleged ‘proto-feathered’ ornithischian which is what I want to turn to now.

Yes, despite all the (justified) palaver, Tianyulong is the second, and not the first ornithischain to be reported with such features. That, perhaps dubious, honour goes to a Psittacosaurus specimen described in 2002 and the reason that this new dinosaur has had so much attention is that problematic work done on the aforementioned animal (for those who have not seen it, you can see a look at a decent image of it here).

First off, the integumentary structures in this one look very little like those seen in theropods (and indeed in Tianyulong, they are longer and stiffer in Psittacosaurus) which made researchers suspicious that perhaps they were not genuine (genuine bits of skin that is, they certainly are biological structures) especially in the light of at least some people wanting to interpret them as homologues to protofeathers. Their narrow distribution on the body (only really on part of the tail, and sparsely at that) hardly looked like a covering for insulation, display or anything else obviously functional, and several researchers have confidently asserted that these are in fact merely plant pieces that are simply in association with the skeleton and not part of the dinosaur itself (and the carbonisation process that seems to work in the Jehol certainly produces fossils of plants and other things that look all but identical to this). Certainly the structure of them is very fine and it would be hard to make any meaningful comparison to other feathered dinosaurs without better specimens. There are other Psittacosaurus specimens known from the Jehol which do have soft tissues preserved (and hundreds if not thousands of skeletons from outside) and none of which show such structures which again implies that these were not real. In addition, ceratopsians such as Psittacosaurus are derived ornithischians and again with such a big evolutionary and temporal gap between them and the derived theropods (of which there were far fewer feathered examples back them) it was difficult to draw good parallels. Finally the specimen is of, let’s say ‘questionable legality’ with regard to its export from China, and a large number of researchers have refused to work on it as a result meaning it has not been examined by some key researchers and relatively little work in general has been carried out on it. they are longer and stiffer in

When you add all that up you can see why the specimens was and has been treated with quite a bit of caution, and as a result why the new one has got so much acclaim. It remained a possible example of a derived ornithischian with some kinds of modified integument, but equally it was very problematic for practical (making comparisons and a lack of corroboration) and philosophical reasons (both in terms of evolutionary theory and the legality of the material). However, in the light of the Tianyulong it seems that more attention will have to be paid to this specimen.

The fact that we do now have something that shows with far greater clarity and certainty that such structures are in the Ornithischia, and with a heterodontosaurid showing them the evolutionary gap between derived theropods and ceratopsians has been narrowed considerably. It certainly gives more credence to the idea that other ornithischians had such structures and corroboration from other specimens of these two and other taxa will be eagerly sought.

What interest me particularly is that in both cases there is a concentration of these things on the base of the tail which certainly supports the case for the Psittacosaurus specimen being genuine. However it still does not explain the odd pattern of structures in the ceratopsian or why they might be present at all. At the risk of leaving a lamentably obvious and unhelpful closing line, this really is the next twist in a long saga over feather evolution and indeed skin evolution in general in dinosaurs and reptiles as a whole and certainly opens up new possibilities and provides new evidence, but, as ever, more reseach is needed.

27 Responses to “Blah blah feathered ornithischians yawn”

  1. 1 Richard 19/03/2009 at 7:49 pm

    Some interesting points Dave. But with regard to your point 5 how many dinosauromorphs, basal theropods, basal sauropodomorphs, basal ornithischians (ignoring Tianyulong) are preserved in deposits that preserve soft tissues? Off the top of my head I think the answer is almost none. These integumentary structures could easily have been widespread. We urgently need a terrestrial Lagerstatten somewhere in the Middle Triassic-Early Jurassic…

  2. 2 David Hone 19/03/2009 at 8:06 pm

    That is true of course, but then we do have a bunch (in not large numbers) of skin impressions and fossilsied for various taxa with no signs of any kinds of filaments etc. so that point is partially supported, kind of.

    I really just wanted to emphasise caution on interpretation when I havbe already seen a couple of blogs stating that these are homologues when the paper makes it quite clear, even explicitly clear that this is only a possibility right now.

  3. 3 Richard 19/03/2009 at 8:11 pm

    You’re right of course to be cautious, but again I think the skin impressions are almost entirely for post-Middle Jurassic large-bodied taxa. I think it’s entirely possible that filamentous integument could have been widespread amongst small-bodied basal dinosaurs but we need exceptional preservation to test this. Absence of evidence isn’t evidence of…etc etc.

  4. 4 David Hone 19/03/2009 at 8:33 pm

    Well yes as ever I take that point too, you can’t overlook it. I would just really like there to be something from more basal groups, or another definitive ornithischian or two before even starting down the ‘all dinosaurs were fuzzy’ route. Of course it’s a possibility, perhaps even a strong one, but give the issues with the psittacosuaur specimen, there is also a tendency here (by some) to make a trend out of one data point. Two classics really and here opposing each other, do we risk overinterpreting one specimen to apply to all (or even many) other taxa, or treat the lack of corroboration as a genuine lack of that feature rather than jsut a lakc of speciemns. Pays your money and tkaes your choice I suppose.

    At the risk of then getting entangled in the ‘did only small taxa have such coverings?’ issue which might only make things worse, you are right that there are few skin impressions for stuff at the bottom end of things (bar the base of the feet, which hardly count, obviously) and / or for smaller taxa, but there are quite a few impressions etc. for Cretaceous taxa of various clades. IF this was very prevalent in Ornithischia as some people think / hope then again you might expect to have found a few more examples by now.

  5. 5 Søren Rafn 20/03/2009 at 4:08 am

    Maybe these structures are merely modified spines? I am not very much into dinosaur morphology but are working with asian theraphosid spiders. In these you will find spines and setae which are ranging from flat rounded knobs, stout spines, dagger-like, club-like and clavate- filiform- plumose- setae. Basically all from the same kind of spination. What I am pointing on is that as far as I remember there has been some dino skin impressions that showed knobs, nodules and such. Is it possible that the hairlike filaments are merely such skin structures that have been extremely elongated? Just my five cents 😉

  6. 6 Zach Miller 20/03/2009 at 9:13 am

    Hmmm…I’d wondered why more work hadn’t been done on that famous Psittacosaurus, so thanks for answering that one.

  7. 7 David Hone 20/03/2009 at 12:11 pm

    Soren (sorry, can’t do the O peoperly in your name), you are not too far from the mark. These various feathers and filaments and annoying but suitably named ‘integumentary structures’ are themselves modified skin / scales in any case. It is pretty certain that those in the Psittacosaurus are also (if real) made from skin or more likely sclaes, the question is are they homologous with those seen in the others, or did they evolve independently? It could be that they are simply like some kind of wierd rachis or modified feather (think of the long plumes of a peacock’s tail without the eye-spots – it would still be a feather and homologous with feathers while not looking very much like one anymore) but currently we jsut don’t know.

  8. 8 Roger 21/03/2009 at 11:41 am

    I don’t know if you’ve read much about the Early Cretaceous site I work at on the Victorian coast (Flat Rocks, near Inverloch), but we have a few basal ornithopods—formerly classified as hypsilophodonts—that were probably active during the three months of polar darkness. John Long has speculated that they may have been feathered or fur-covered in order to stay warm in these frigid conditions; this discovery gives some credence to that notion. Add to that the possibility that our hypsis burrowed like the one in Montana, and you’ve got some pretty funky little dinosaurs!

  9. 9 David Hone 21/03/2009 at 2:13 pm

    That does sound cool Roger. Sorry but I’m not up on my ornithischians or Auzzie dinos so I had largely missed this stuff. Thanks for sharing.

  10. 10 P-Easy, K-Shizzeh [PenaltyKillah] 07/04/2009 at 10:43 pm

    Yikes! Feathers are a paleontologist’s enema.

    I suspect those Ornithischian “feathers” are just shaggy furlike material to keep dinosaurs like Tianyulong warm. They come off in the summer. So there!

  11. 11 David Hone 08/04/2009 at 7:59 am

    I’m not really sure what your point is there. I am cautioing against calling them feathers (as indeed did the authors of the paper). They are still an integumentary structure, the question is are they homologous to feathers or not. Ands as for keeping them warm, this animal lived in a tropical environment so a ‘winter coat’ seems pretty unlikely, especially as it only seems to cover the spine and not the flanks, nor is it fine and thin like an insulating layer would need to be to trap air.

  12. 12 Joshua Dyal 15/04/2009 at 3:47 am

    Caution is well and good, but too much of it makes one start to wonder what exactly is going on. If these are indeed “protofeathers” similar in nature to those of more basal coelurosaurs, then the most parsimonious explanation is that they are indeed a synapomorphous feature. Of course, maximum parsimony isn’t necessarily “right” but with a judicious caveat, it can still be applied as “most likely.”

    For that matter, I suspect personally that we’ll eventually find that the “proto-feather” structures in dinosaurs and the “ptero-fuzz” are synapomorphic features that underwent further derivation to became pennaceous feathers on the run up to birds, and that the controversial impressions around Longuisquama will prove to be very early versions of the same feature. But that is putting the cart before the horse a fair bit.

    My point is; I can understand the point of being cautious and not rushing forward too fast to make a judgement here, but at some point the scientific establishment starts to come across as overly conservative sticks-in-the-mud when divergent lines of evidence—much of it circumstantial, to be sure—all starts pointing the same way and yet all we hear are cries of caution. And all of that to NOT make a parsimonious deduction!

  13. 13 David Hone 15/04/2009 at 7:16 am

    But currently I do not think ti is the most parsimonious deduction without confirmation that the features are homologous and at least soem of that can come from examining their strucutre in detail which has yet to be done. I am most cautious about using the term ‘feather’ as that is heavily loaded, and as I note above these cannot be featers rather by definition, not tat does not make them not homologous with feathers. We really do need better evidence to confirm a direct assocaition, or at least more ornithischians / basal theropods with simialr strucutres. I honeslty think it will come, but as you say, to cliam that already is jumping the gun.

  14. 14 Joshua Dyal 15/04/2009 at 8:49 pm

    True; I’m assuming that the structures are what they claim to be. That assumption may be unwarranted, and that seems to be the biggest area of caution.

    However, I’m surprised as I’ve read the reactions to this, of a lot of talk about convergent and parallel evolution of feather-like structures, and paleontologists being all thrown for a loop and confused by the find. Maybe it’s easy for me because I EXPECTED that something like this would turn up someday (although my money was on finding it on a “hypsilophodont”, not a heterodontosaur) so the possible implications don’t seem unusual to me at all. But, again, assuming that these trace fossils are in fact what they are claimed to be, how is making the conclusion that they are a synapomorphous structure that goes back to before the Ornithischian/Saurischian split not become the most parsimonious explanation?

  15. 15 David Hone 16/04/2009 at 9:20 am

    I dont’t think you need be too cautious about these being genuine strucutres and not fkaed, part of a plant, or a chiumeric fossil (see the post I did on Chinese fakes with respect to this).

    As for the homology issue, I think it’s a function of exactly when and where these things appear. As I said, we still have no basal theropods, no sauropodomoprhs and no other ornithischains with these things. While there are structures in pterosaurs thier phylogenetic poisiton is uncertain. As a result we only have these in derived theropods and 1 or 2 ornithischians. If you map that on a phylogeny you are left with mutiple gains and losses however you do it (gain at the base of Dinosauria / Ornithodira, then loss in Sauropodomoprha, loss in derived ornithischia, or independent gain in Tetanurae and Heterodontosauria). When you include the possibe absence in Ornithomosauria it gets still more complex.
    Obviously this is heavily infulenced by our lack of specimens from certein times and places – if we have a few more Triassic and Early Jurassic lagerstaaten this may fx the issue and in general ornithischhians are pretty rare in the Jehol and Dahougou, so perhaps we are just not finding them.
    I think therfore there that the caution is valid without further evidence. There is a strong possibility that these are homologous (or derived from earlier homologous structes, making this perhpas parallelism rather than convergence or strict homology) but right now we don’t know. There is, obviously, evidence that these features may have already arisen multiple times (depending on what you do with pterosaurs, and of course generally speciliased scales in reptiles are common – osteoderms come and go regularly, veraious skin frills and webbing comes and goes as do enlarged scales and horns in things like iguanas – reptiles are potentially quite plastic in their integumentary evolution) which also cautions against saying ‘these are homologous’. May prople probably think they are already, but personally I want to wait for more evidence and a better understanding of what these are. We have yet not had a detailed analysis of the structures of the ‘things’ in Tianyulong – it may be that they are quite different in detail to those of say Beipaiosaurus, or almost identical and that alone might swing the balance. I’m going to wait and see.

  16. 16 Joshua Dyal 18/04/2009 at 4:29 am

    Well, that’s certainly fair enough. I’m probably guilty of being a little over-enthusiastic to come to the conclusion that I wanted to, and which I already believed and was just waiting for the right evidence to prove in the first place.

  17. 17 David Hone 19/04/2009 at 1:44 pm

    That’s about it. There is *some* ecidence that this is truly homologous with those of the saurischains, just not *much* as of yet. It will, I suspect, come, but until then it’s not so much bet hedging as natural scientific caution and parsimony to assume that this is only a possibility and not a probablity until we know more.

  18. 18 Django 02/03/2011 at 5:33 am

    Longisquama has been showing up as basal lepidosauromorph in a lot of cladograms recently, and it’s not really even clear what its structures are. Other than that, I agree with you.

  19. 19 Django 03/03/2011 at 10:17 pm

    Crap! I meant basal diapsid.

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