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Sinosauropteryx: not fuzz-less (long)




Jerry made some good points (for and against) the Lingham-Soliar et al paper, although he was more generous than I can manage after two readings of it. I urge everyone to read the paper, but in brief: Lingham-Soliar (et al) examined a new(ish) specimen of Sinosauropteryx (IVPP V12415) under a conventional microscope, and argue that the preserved soft tissue morphology is consistent with collagen, hence presto-change-o there are no protofeathers on any Sinosauropteryx specimen. Their own photos of specimen NIGP 127587 (figure 4a) seem to indicate two very different tissue types, one with extensive parallel fibers that are almost certainly not epidermal insulation, and a dorsal surface that does resemble proto-feather epidermal structures as described in the type specimen of Sinosauropteryx (and other bird and feathered dromaeosaur specimens). To explain this (and the proto-feather appearance of the type specimen) they postulate that this difference in morphology is due to "taphonomic degradation" of the collagenous tissuse, and cite the soft tissue preserved in the dorsal region of the neck of IVPP V12415 as representing an intermediate stage of decomposition (Fig. 2c), linking all of the preserved fiber types.


Their analysis is deeply flawed:

1) Despite David Marjanovic's assertation that Lingham-Soliar is an authority on collagen, little of that expertise is evident in this paper. To begin with, they never actually provide a method (e.g. morphology, chemistry, etc) to distinguish fossil collagenous tissue from other fiberous tissues in vertebrate bodies (e.g. muscle and elastic tissues). In particular, the tissue at the base of the neck of IVPP V12415 (figure 2c) is almost certainly not collagen. They note themselves that the _straight_ parallel fibers seem to converge from the neck towards "a point". That "point" is near the cervico-dorsal juncture, running from there to the posterior cervical vertebrae (http://skeletaldrawing.com/ext_photos/sinosauropteryx_stuff/fig2c.jpg). This is an excellent match for the cervical musculature of birds, and is also not dissimilar to the elstic ligaments seen in ratites. There are similar fibers running parallell between neural spines of the vertebrae (to clarify you can see the same image with photoshoped lines parallelling the fibers here: http://skeletaldrawing.com/ext_photos/sinosauropteryx_stuff/fig2c_fibers.jpg).

The fibers at the base of the neck not only resemble the neck muscles of birds in their location and orientation, they taphonomy practically demands that they be contractile or elastic fibers of some sort. The fossil is in the classic death pose, with the neck dorsaflexed well beyond the normal life position. This dorsaflexion pulls the neck back and shortens the tissues on the dorsal side of the vertebrae. Collagen fibers are not elastic, and they don't "shrink" like muscles and elastic ligaments will; if those straight fibers were collagen the neck could not have ventroflexed back into life position! Since collagen fibers are non-elastic, have tensile strength, but no comporessive strength a collagen frill on the dorsal margin could not be under tension with the neck pulled back. Collagen fibers in this situation would look more like this:

http://skeletaldrawing.com/ext_photos/sinosauropteryx_stuff/collagen.gif

Since the fibers of the neck are all clearly shortening substantially to take up the slack created by the death pose, they have to either be elastic fibers or muscle fibers. The latter seem more likely to me, in light their similarity to bird cervical musculature. Lingham-Soliar do not even attempt to explain these problems, and appear oblivious to the fact that a dorsally located collagen frill should not exhibit linnear fibers while the neck is retracted.

In short, they are clearly correct that the cervical fibers in this specimen are not epidermal insulatory structures, but they fail to make the case that the fibers are collagenous, let alone dermal in nature.

2) Establishing that the structures are either dermal or epidermal (or less superficial altogether), and either muscular, elastic, or collagenous is problematic on all the fibers preserved in IVPP V12415. Similar arguments apply to the tail (Fig 2 a & b); in particular, the supposed tail "frill" section with a solid dorsal margin exhibits a more gradual curve than the neural spines that it would overlay, looking more like taught tissue that has partially pulled away from the tail as it contracted, rather than a feature that extends the entire length of the tail (you can actually see it disapearing distalling the figure 1a). The taphonomy is consistent with this, as while assuming the death pose the main portion of the tail has actually pulled away from the tail tip and an otherwise articulated portion of chevrons. There was clearly enough connective tissue/musclature to hold portions together and pull the tail into the death position, but decay was also advanced enough that the caudal vertebrae were ripped away (while remaining otherwise articulated) from the chevrons and tail tip, which themselves remain in articulation. To claim that these fibers (which look different from the type specimen) are homologous with the structures seen in other specimens without the type of detailed comparison that the authors' themselves decry in other studies(!) is beyond careless: it's special pleading.

3) Taphonomy... speaking of special pleading... The paper attacks previous authors for ignoring the roll of taphonomy, and then...completely ignores the taphonomy of their specimens! For example, they repeatedly refer to the possible roll of wind and water "erosion" to play a roll in breaking down connective tissue into the appearance of insulatory structures, but don't even make a passing mention of the actual depositional environment of these specimens. Since current consensus is they are from low-energy fine-grained shallow lakebed sediments there is no evidence of significant water currents (it would take a lot to break down collagen) and wind seems unlikely underwater, to say the least.

4) They also show a photograph (Fig 4) of the tail of NIGP 127587. Despite claims in the paper, the photograph shows a dorsally located layer (apparently) consisting of dino-fuzz style insulatory structures, and a ventral layer of rigorously parallel non-epidermal fibers that are clearly not dino-fuzz (the taphonomy does not distinguish between collagen/elastin/muscle fiber hypotheses in this specimen like it does in IVPP P12415). Unless it is a trick of the lighting, the photograph seems to indicate the epidermal/insulatory layer is preserved on a more superficial layer of rock than the collagen/muscles fibers are. Worse yet, the proto-fuzz type fibers clearly extend down most of the way past the tail, indicating it is not a midline stucture.

5) Finally, the tone of the paper is inexcusible (to me). Even ignoring the hypocrasy of chastizing previous studies for failure to consider taphonomy and do proper comparative work...while ignoring taphonomy (if not outright contradicting it) and failing to do detailed compartive work, the intro and conclusion is rife with phrases urging us to avoid "recourse to arbitrary conjectures on feather origins" (discussion section) that "strengthened the resolve of many palaeontologists that
birds are direct descendents of theropod dinosaurs." (introduction) This type of pejorative wording is distasteful enough on cable news shows; it has no place in scientific publications (well, perhaps in an editorial).


In summary, the paper spends a lot of time accusing other studies of the same flaws it commits. The paper fails to make a good case that the fibers of IVPP V12415 are collagenous (especially the cervical tissues) or epidermal in nature. It fails to link the fibers in IVPP V12415 to the proposed proto-feathers of the type specimen, and in fact presents a photograph that appears to contradict the idea. They fail to provide a plausible mechanism that would decompose collagenous tissue into the appearance of insulatory strucutres, and the mechanisms they do postulate directly contradict the actual taphonomy of the specimens.

Hopefully this paper will be the stimulus for further research into the nature of the fibers preserved in Sinosauropteryx, feathered dinosaurs, mammals, etc. from Liaoning. In the meantime, let's all strive to write more papers taht are more responsible than this one, regardless of conclusions.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

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