Feathered Dromeosaurs

21 02 2007

A few weeks ago I pondered whether it was accurate to say that all dromeosaurs (i.e. Velociraptor, Deinonychus, Utahraptor, etc.) had feathers based upon the possesion of feathers and feather-like integuments on fossils like Microraptor gui, Cryptovolans, and Sinornithosaurus, stating that perhaps it wasn’t the most responsible thing to say that all later dromeosaurs had feathers because of their presence in some of the basal forms coming out of China. The esteemed paleontologists Dr. Thomas R. Holtz and Dr. Mark Norell both responded to my queries, helping to illuminate the issue for me. Dr. Holtz had this to say;

Actually, at this point there are several feathered dromaeosaurid fossils: a couple specimens of Sinornithosaurus and the many specimens of Microraptor (incl. Cryptovolans). More to the point, there are no specimens of the integument of any dromaeosaurid lacking feathers, nor are there any specimens of dinosaur phylogentically closer to Aves than Dromaeosauridae that lack feathers. Even more, the specimens for which we have integument for the next series of outgroups to the dromaeosaurid-bird clade (oviraptorosaurs, therizinosauroids, alvarezsaurids, and Archaeoptyerx and Pedopenna, if they wind up there) have either honest-to-goodness feathers or protofeather fuzz.

Thus, the simplest inferences is that true feathers were already present in the common ancestor of Dromaeosauridae + birds. While loss of this trait in any given branch is certainly possible, to infer such a change without positive information is dishonest.

Our inference that all dromaeosaurids were feathered is the same inference that monotremes were furry.

Given the current evidence, it is up to those who argue for non-feathered dromaeosaurids to provide a reason to argue for that position, as the evidence supports feathered “raptors” as the basal condition.

Indeed, dromeosaurs had a suite of characteristics that are more derived and closer to birds than Archaeopteryx, so if any of the dromeosaurs lost feathers, as Dr. Holtz notes, we would be left to speculate as to how this occurred. Unfortunately preservation as exquisite as seen in the fossils coming out of China is rare, so North American dromeosaurs may have feathers that were not preserved because of taphonomy. Dr. Norell also had this to add, via personal communication;

From a parsimony perspective we would predict that all dromaeosaurs had feathers at least during part of their lifespan. That is not to say that they were completely covered with feathers like Microraptor is. Because both avialans, some dromaeosaurs, a troodontid, and oviraptorosaurs are known to have feathers, and the explanation for this is that they are descended from the same feathered ancestor, we would predict that all of the animals descended from this ancestor (velociraptor,Citipati, deinonychus, troodon, wetc.) would also have been feathered. That is the same argument we use for other groups. For instance we have just as much evidence that Velociraptor was feathered as we do that australopihticines like Lucy had hair. Hope this helps.

This is closer to what I originally intended to write before getting carried away on a tangent; I am not in protest of dromeosaurs having feathers but how do we know if they retained them during their entire life? Could it be possible that certain types of feathers were selected against or that “fuzz” was more adaptive for some dinosaurs than full blown feathers? The Lucy comment also reminds me of something my wife brought up when visiting the American Museum of Natural History this past weekend; we know Lucy had hair, but how much? In any reconstruction there is the information you have and then the inference you make, so even though I am not one to dispute that Lucy had hair or that most dromeosaurs had feathers for at least part of their lives, how do we know how much of the body was covered, what the structures looked like, what color? The issue of losing feathers or having feathers while a juvenile but not as an adult also has this problem; because of the way fossils are preserved it could be that a dinosaur like Utahraptor did not have feathers but because of its ancestry it could be inferred it had them, the door always open to it having feathers. There is always the possibility of one being found with the structures, so unless we find a specimen in an environment where the preservation is so exquisite that skin and soft parts are preserved without feathers, the best inference based on parsimony is that at some point it had feathers.

I think parsimony is a good measuring stick for science and certainly should be heeded; it definitely has helped weed out some really bad ideas over time. Even so, I wonder if it always works with observations, and I wonder if there are some instances where the simplest answer isn’t the correct one or there is more to the story than we currently know. This is not to say that we should disregard parsimony or entertain hypotheses of “ancient astronauts,” man living with dinosaurs, etc., but when I encounter a question of problem there’s always a part of me that wonders about if there is more to the story than I now understand. Maybe it’s because I’m trying to understand ecology and evolution together, as to me you can’t fully understand one without the other (species do not involve in a vacuum, but are shaped by their environment), and unfortunately when it comes to the fossil record there are more questions than answers when it comes to paleoecology at present. In any case, I am most thankful to D.r Holtz and Norell for setting me straight and clarifying things a bit, although I still think when it comes to reconstructions of dromeosaurs where we don’t have actual physical evidence of feathers at present it should be made clear that such reconstructions are based on inference and are speculative. Once again, I’m not suggesting such reconstructions are without merit, they are certainly our best hypotheses, but if we do not at least leave open the possibility that we are mistaken about what these animals looked like when more evidence is requireed, we have moved beyond science and into a kind of dogma, detrimental to all. I am certainly excited by the new finds of feathered dinosaurs and I think scientists should do more to tell people about these amazing fossils; the notion of feathered dinosaurs is popular but I’ve yet to see any documentary that goes into the topic in detail (then again I’ve haven’t had TV for almost a year). I can only imagine what else lies in the strata between the Jurassic and end-Cretaceous that will help us better understand how dinosaurs came to fly.



2 responses

14 06 2007
InWeDay 2007 « Laelaps

[…] with people you wouldn’t otherwise get to meet. I’ve been lucky enough to have Thomas R. Holtz comment on some of my assertions about feathered dinosaurs, J. Judson Wynne correct a mistake I made about […]

12 11 2015
Flat dinosaurs | K. M. Carroll, Author

[…] egg-shape. They draw them long and snakey, like the lizards they supposedly evolved from. Oh wait! You mean ‘feathered dinosaurs’ have always had feathers and nobody has found any transit… Like, maybe they’re just […]

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