Meet Dave:
NGMC 91, aka “Dave.”
Dave is the nickname for a particularly interesting and complete specimen of dromaeosaurid. It is also called NGMC 91, a specimen designation. It has been referred to the taxon Sinornithosaurus [1], but the authors considered that it was potentially viable it was a new species and so did not refer it to the only known species (at the time), Sinornithosaurus millennii [2]. (Currently, there are two species, now supplemented by Sinornithosaurus haoiana [3].)
There’s a lot to be said about Dave. Here’s a few oddbits.
1. Dave, unlike many fossils from the Liaoning lagerstätten, is not just covered in “dinofuzz,” but is completely covered in it. The only region of the body that seems to not bear any filamentous integument is the foot (which preserves scales) and the tip of the nose (which doesn’t seem to preserve anything in detail).
2. Dave is covered in a variety of different types of integument, from thin filaments (stage 1 feathers of [4]), bound and bunched clusters, and a pennaceous “true” feather.
3. These are not distributed around the body in converntional forms: The pennaceous feathers are not barbulated, preserving only the barbs and rachis. Thus, they are not truly “vaned.” This type of feather occurs in birds today, and is considered both degenerate from a true vaned plume, and as an antecedant to it [4]. These features are known in Dave only at the tip of the tail and in the base of the hindlimb. They are not present in the forelimb, or elsewhere on the hindlimb. In direct contrast to Microraptor gui [5] (a closely related taxon), the arm and leg did not have “wings.” Sinornithosaurus millennii also doesn’t seem to have true “wings,” as filamentous integument are found on the arms of the holotype [2].
4. Dave is not an adult, it seems: Portions of its body appear juvenile, including the proportion of the head to the body, and of the limbs to the body, while many features suggest it is a specimen of Sinornithosaurus millennii. It’s not unlikely that the specimen is its own, unique taxon, related to Sinornithosaurus millennii, but it has been considered less likely in the extent that it is preferable to not name juveniles as the basis of taxonomy when there are also likely adults present.
5. Dave is strange. Several bones of the body are actually longer than those of Sinornithosaurus millennii, despite variation in the proportions and indications Dave is a juvenile of the other taxon. This is one good reason why Dave is not always considered a specimen of Sinornithosaurus millennii, even if it is still a juvenile. Ontogeny is not well understood in dromaeosaurids due to a lack of juveniles but also because microraptorian dromaeosaurids are even more different from conventional dromaeosaurids due to their skeletal features, proportions, etc. .
Dave’s Feathers
So what does that mean? Dave is important, and not fully described, which makes much of this preliminary. But there are certainly several things we can glean from what is presented to us. First, let’s compare the two taxa we’re talking about:
Sinornithosaurus millennii and “Dave” compared.
Dave is pretty small, although larger than Microraptor zhaoianus, and has some odd proportions: a very short tail, a large triangular head, and relatively shorter arms. These seem to be ontogenetically younger features. But scaling does not compare among other animals, for some of Dave’s limbs are very close to the “adult” size, despite other portions being vastly smaller. It is likely a subadult, but is it necessarily a subadult of Sinornithosaurus millennii? That’s left Dave in the grey area phylogenentically.
Dave is also particular for preserving a variety of integument. This includes simple filaments, complex basally-branching filament bundles, and long raches with barbs, effectively plumulaceous feathers. The last set are only know from the rear of the leg, and are limited to the thigh. You can see this distribution below:
Skeleton of “Dave,” based on NGMC 91, with overlays of integumental structures. Blue, single-filament “stage 1 feathers” and basally-bound branching filament “stage II feathers” interspersed across most of the body; Red, plumulaceous central-rachis “stage 3 feather” arising only from the femoral region; Green, scales around the metatarsus, without traces of feathers.
IVPP V12811, the holotype of Sinornithosaurus millennii, preserves only “stage 1 feathers” (see [4]), around the legs, chest and arms, and tail, where they are present in NGMC 91. But the latter specimen elaborates this, while showing that the tip of the snout and the feet were likely unfeathered. Some have argued, however, that despite this, the integument can be adapted or expanded beyond the preserved or likely limits of what we’ve found, but I’ll get to that in a later post.
Dave tells us that there’s more about integument evolving in theropod dinosaurs than we know, and that modern avian feathers, derived from a core model, are all exapted from a type III-IV feathers [4], but many of their precursors lacked any such thing as a modern avian feather. Dave’s feathers lack barbules, which link barbs together and are inherent to the form of a pennaceous feather (you cannot have a “vane” without barbules, as the barbules link the barbs into said structure). Yet despite this, Dave also has some feathers around its pollex (“thumb”), which may be termed an “alula” with only the faintest twinge of regret. That’s because the alula in birds certainly arises from the first digit (mdI), but in this case it likely have to do with the fact that, with the apparent exception of the tip of the snout and the actual exception of the tarsus and pes, Dave is entirely coated in feathers, including the entire manus [see above].
[1] Ji Q., Norell, M. A., Gao, K.-q., Ji S.-a. & Ren D. 2001. The distribution of integumentary structures in a feathered dinosaur. Nature 410:1084-1087.
[2] Xu X., Wang X.-l. & Wu X.-c. 1999. A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China. Nature 401:262-266.
[3] Liu J., Ji S.-a., Tang, F.-c. & Gao, K.-q. 2004. A new species of dromaeosaurids from the Yixian Formation of western Liaoning. Geological Bulletin of China 23(8):778-783.
[4] Prum, R. O. 1999. Development and evolutionary origin of feathers. Journal of Experimental Zoology 285:291-306.
[5] Xu X., Zhou Z.-m, Wang X.-l., Kuang X., Zhang F.-c. & Du X. 2003. Four-winged dinosaurs from China. Nature 421:335-340.
Jaime A. Headden
The Bite Stuff 
Now that’s one gorgeous fossil.
Yes, little Dave is certainly one of the best preserved of the Liaoning fossils available.
Do you think that Dave is a secondarily flightless bird?
As it was a dromaeosaurid, no, it was certainly not a bird. It’s ancestry, with one general dissent, tends to point at an ambiguous polarity in regards to whether or not IT’S ancestors were capable of any form of “flight.” If it were descended from parachuters or gliders, and it seems that Microraptor and Archaeopteryx were incapable of flight itself, then it would NOT be secondarily flightless. Note that Dave is, currently, referred to Sinornithosaurus.
By “one general dissent” do you mean folks like Feduccia, Paul, Martin, etc?
People who present the idea that non-avian maniraptors were secondarily flightless?
Actually, I am pointing only at Paul, who wrote a very well-read and accessible book on the subject. The issue with Feduccia or Martin is entirely different, especially as it has morphed to accept things it formerly fought against. They, unlike Paul, assume that maniraptorans can fly and do not derive into flight-less forms unless they are like typical birds which become flightless for various reasons. This “secondary flightlessness” is not only hard to quantify, it has virtually no phylogenetic utility (save that it does not seem to reverse), and implies that the forms that precede CAN fly. As I mentioned before, a recent study suggests that Archaeopteryx would not be able to “fly” in the sense of propulsion and sustainable lift above a glide trajectory due to its feather construction, although the precise abilities it had seem unknown [1]. And if Archie cannot fly, even in Paul’s scheme, then the whole 2nd flightlessness theory begins to crumble.
[1] Nudds, R. L. & Dyke, G. J. 2010. Narrow primary feather rachises in Confuciusornis and Archaeopteryx suggest poor flight ability. Science 328:887-889.
Could Dave fly?
Dave is a juvenile and lack pennaceous feathers on its arms; the shoulder is undescribed, and it has a lot to do with determining muscle position and orientation; and the wrist appears to be certainly unfused and the carpals small rather than large. So, no.
http://en.wikipedia.org/wiki/Archaeopteryx
“Archaeopteryx is not thought to be a true ancestor of modern birds but, rather, a close relative of that ancestor (see Avialae and Aves).”
So whether Archaeopteryx could fly or not, does not invalidate or validate Paul’s ideas.
It invalidates the premise of “secondary flightlessness” as a concept which has any sort of meaning beyond morphological adaptation. I will eventually get around to discussing Paul’s theory, if you’d like to withhold commenting until then on the subject, because I have relevant posts on the topic in preparation (of which Dave was only the first).
Thanks for the interesting post!
“Dave’s feathers lack barbules, which link barbs together and are inherent to the form of a pennaceous feather (you cannot have a “vane” without barbules, as the barbules link the barbs into said structure).”
Does this mean, then, that Dave’s feathers were like the ones modern ratites have? As far as I see, they lack barbules and make the birds look “hairy” instead of feathery.