Image via Wikipedia I said I'd blog about this, so here goes...

Back in April of this year, David Baum (a professor of botany at the University of Wisconsin) and Susan Offner (a Massachusetts science teacher) wrote an article in The American Biology Teacher titled "Phylogenetics & Tree Thinking". Overall, this was a fairly good article, but there was one major flub up in my opinion.

Nearly at the end of the article, they wrote:
"...students will be amazed and inspired to learn that Tyrannosaurus rex had feathers (Xu et al. 2004), putting the origin of feathers well before the origin of flight."

However, what Xu et al. actually wrote was:
"The presence of the similar structures in IVPP V11579* provides the first direct evidence showing that tyrannosauroids possessed protofeathers. Furthermore, the filamentous protofeathers are branched as in other coelurosaurians. This is a distinctive morphological feature of modern feathers, suggesting that this important modification occurred early in coelurosaurian evolution. Large, derived tyrannosauroids were reported to have scaled skin, but the presence of two kinds of body covering is not unexpected. However, current understanding of the integumentary morphology in non-avian theropods is hindered by poor information on distribution. Given the diverse morphologies of integumentary structures in living birds, it is possible that non-avian theropods had different integumentary morphologies on different regions of the body, and derived, large tyrannosauroids might bear both scale-like and filamentous integumental appendages. Alternatively, the lack of filamentous structures in derived tyrannosauroids is correlated with the large size, a physiological strategy also adopted by some mammals such as elephants, which lose most of their body hairs as they mature." (Xu et al., 2004: 683)

* - Dilong paradoxus

I pointed this out in my response to Baum and Offner with two basic points:
1. There is a lack of direct evidence for feathers in Tyrannosaurus rex.
2. Xu et al. (2004) did not explicitly state that Tyrannosaurus rex had feathers, they only suggested it as a possibility (and even offered some reasons why it might not have--such as the presence of scaled skin in other derived tyrannosauroids which might imply a similar absence of feathers in Tyrannosaurus rex).

I also suggested a more contentious point, that Dilong paradoxus had not been recovered as a basal tyrannosauroid in a cladistic analysis of coelurosaurs by Turner et al. (2007), leaving no evidence for feathers in tyrannosauroids.

To this, Baum and Offner offered this reply:
"Based on the phylogenetic inference that the feather-bearing dinosaur Dilong paradoxus is a tyrannosauroid and the fact that the sister clade (including birds) of the tyrannosauroids also had feathers, Xu et al. (2004) reasoned that all tyrannosauroids probably, but not certainly, had feather-like structures. We are grateful to be informed that Dilong may not be a tyrannosauroid (Turner et al. 2007, supplemental Figure 1), rendering the Xu et al. (2004) conclusion questionable. This is an excellent example of the dynamic nature of phylogenetic knowledge, especially in regards to fossils, for which the lack of DNA sequence data often makes tree reconstruction imprecise. We believe that students can readily be engaged by a question such as: Did T. rex have feathers? The resulting discussion will highlight the various sources of uncertainty that scientists must consider, and how rigorous evolutionary conclusions can be arrived at once one understands phylogenetic reasoning."

Baum and Offner did not address the point I gave in my comments:
"Martin and Czerkas (2000) noted the presence of skin impressions preserving scales in other derived tyrannosauroids. "

They accepted my point about Turner et al., however. But Tom Holtz emailed me with a comment that I think is substantial (and I hope he doesn't mind me pasting it here):
"However, I would point out that using Turner et al. as evidence against a tyrannosauroid position for Dilong is extremely weak, as that matrix has very little anatomical or taxonomic coverage in the basal coelurosaur part of the tree. Other analyses with better sampling in the relevant part of the tree consistently yield a tyrannosauroid position for Dilong."

He is absolutely right. This wasn't a good argument at all. So effectively, 1/3 arguments I made for the absence of feathers in Tyrannosaurus rex was not valid.

However, because I don't feel this is contentious enough yet, I'll tear down my other arguments.

As I said above, there is a lack of direct evidence for feathers in Tyrannosaurus rex. There is also a lack of integumentary preservation in Tyrannosaurus rex. We have nothing. No imprints showing scales, naked skin, or protofeathers. Nada. Zilch. Likely, we can infer that they had one of the three, but we don't know which.

It's true that skin impressions have been reported in the past, but those haven't been published at all, aside from a brief mention in one paper. As far as I know, no further description or photographs of these impressions exist publicly. We don't know what part of the body they came from or anything about them. It's entirely possible, as Xu et al. suggested, that tyrannosaurids might have had both scales and protofeathers.

So to answer the question of whether or not Tyrannosaurus rex had feathers or not, I'd say the answer is something along the lines of yes, no, and maybe.

If anyone is interested in a PDF of the comment and reply that is exponentially smaller than the one available through BioOne, feel free to ask.

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