More thoughts on Gigantoraptor

I received my pdf copy of the new Nature earlier today and had a chance to look at the paper describing the newly announced Gigantoraptor I blogged about earlier today. If you have a Nature subscription, you can have a look at “A gigantic bird-like dinosaur from the Late Cretaceous of China” by Xing Xu, Qingwei Tan, Jianmin Wang, Xijin Zhao, & Lin Tan at the journal’s website.

[PZ Bora and Grrlscientist have blogged the news as well]

I know Darren from Tetrapod Zoology could do a much better job at describing this find (and because I took an extra day to write this post, he already has, and he provides tons more information on new dinosaurs you probably haven’t heard about yet) and its relevance than I could, but I wouldn’t be much of a blogger if I just waited around to see what everyone else thought and then parrot that. In any case, the first issue that came to my mind was that of feathers; the beautiful painting that has accompanied many of the press releases has Gigantoraptor bearing feathers, (see my previous entry) with Xu Xing stating;

We think it’s the largest feathered animal ever to have been discovered.

Upon hearing that statement and seeing the reconstruction I was hoping for some juicy photos of feathers from a fine-preservation environment, but there aren’t any to show. Xing recognizes this, but still maintains the assertion, stating;

Some experts may not believe this dinosaur had feathers, as it is so big, and we did not find traces of feathers, but from the evidence we unearthed, and all the tests we have done, we are confident in our research.

The notion that this dinosaur had feathers, however, primarily comes from its relationship to dinosaurs on which we have found evidence of feathers. From the Nature letter;

As an oviraptorosaurian, Gigantoraptor is remarkable in its gigantic size, about 300 times as heavy as basal oviraptorosaurians Caudiperyx and Protarchaeopteryx, species known to bear pennaceous arm feathers and other types of feathers as well. A size disparity so dramatic might cause a change of integumentary coverings, such that large-sized forms lose filamentous integuments for insulation, as is the case in some mammals and is inferred for the tyrannosaurs. But Gigantoraptor might have at least retained arm feathers or their homologues from its ancestors, if not other types of feathers, given that the primary function of arm feathers is not to insulate the individual and their development is probably not related to size.

I’ve tread these waters before when contemplating how dinosaurs are portrayed in the media, and while I’m not suggesting that this dinosaur (or Deinonychus or other theropods with avian characteristics) didn’t have any feathers whatsoever, I think that it’s best to be tentative at this point. Evolution may or may not have retained the feathers of this dinosaur, and while it would seem more likely that it had some feathers (potential skin changes would be important to losing feathers as a body covering, which helps to case for a feathered Gigantoraptor), whatever reconstruction we come up with is going to be speculative. Even looking at the reconstructed skeleton above, the gray areas are parts of the skeleton we don’t have, so while we have a lot of important information on how big and impressive this animal was, there is still much to be learned from future specimens that may come to light.

Back to the feather, the Supplementary Information section has this to reiterates the researcher’s main point;

The evidence supporting the presence of feathers on arms and tail of Gigantoraptor is mainly derived from the fact that basal oviraptorosaurs bear pennaceous feathers on their arms and tail. There is no persuasive evidence to expect a loss of arm and tail feathers in the gigantic Gigantoraptor as in some large mammals and possibly tyrannosaurs because arm and tail feathers’ primary function is not insulating the individual and their development is probably less affected by large size. Additional indirect evidence for the presence of feathers on Gigantoraptor comes from oviraptorsaur’s brooding behavior. There is direct fossil evidence supporting the presence of bird-like brooding behavior in oviraptorosaurs. The arm feathers are suggested to be used to brood the nest in oviraptorosaurs. If Gigantoraptor retains this behavior from its ancestry and the Hopp and Orsen’s hypothesis holds true, Gigantoraptor would be expected to bear feathers on its arms. Nevertheless, the presence of feathers in Gigantoraptor needs additional confirmation by empirical evidence.

To put it more succinctly, feathers along the arms or tails of these animals (if present) wouldn’t have caused problems with body temperature as they got larger like a body-covering of feathers might. Plus, the arm feathers might have been useful in covering/warming the nest of a Gigantoraptor brooding over its nest, providing a reason for the preservation of the feathers. Essentially, given that the ancestors of these animals had feathers, and that it might have been difficult evolutionarily to lose feathers, feathers are assumed even if there is not yet direct evidence of them in the fossil. Indeed, as I have been told by several scientists (and is echoed in this paper), if these dinosaurs lost their feathers a mechanism or reason for this loss needs to be given, but unfortunately we do not have an entire series of all maniraptoran dinosaurs exquisitely preserved where the presence of absence of feathers in all types and ages could be determined. I’m not saying “Don’t you dare draw that dinosaur with feathers,” but merely “Hey, let’s be careful about this.”

Indeed, as I noted in the last post many media outlets are claiming that this new dinosaur throws a monkey-wrench in the hypothesized evolutionary origin of birds. While Gigantoraptor does have some very bird-like characteristics we wouldn’t expect to find (especially in the femur, which isn’t as bulky as that of a Tyrannosaurus), it doesn’t mean that birds really originated from giant maniraptorans like the reports seem to imply. As I noted yesterday, the bird Confuciusornis predates Gigantoraptor by more than 30 million years, so Gigantoraptor is not rewriting history in the way that some have suggested.

Truth be told, however, I am an amateur compared to other bloggers out there, so please have a look at these links for more informed opinions on the new dinosaur.

Tetrapod Zoology: Gigantoraptor, Eocursor and… baby Toni [This is required reading, no excuses!]
Hairy Museum of Natural History: Gigantoraptor!
DinoBase: Gigantoraptor erlianensis: a gigantic oviraptorosaur!

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