Lingham-Soliar's Comments on Fossil Preservation -- Redux

[Jaime Headden <qi_leong@hotmail.com>]

  Previously, we were joined with Lingham-Soliar (hereafter TLS) on the 
argument that the tissue structures in "dinobirds" were degraded collagen. 

  See 
http://qilong.wordpress.com/2009/09/22/lingham-soliars-review-of-chinese-fossil-preservation/
 for a full accounting of this discussion.

  Since the last time I posted on this topic, TLS has published a commentary 
with G. Mayr on the topic of *Psittacosaurus* integument, but this story has 
become a little more convoluted. For you see, TLS has not only published two 
further papers on the subject of integumental structure, but two other papers 
have also come out on the topic with the recovery of putative melanosomes in 
various fossils.

  Lingham-Soliar, T. & Plodowski, G. in press. The integument of Psittacosaurus 
from Liaoning Province, China: Taphonomy, epidermal patterns and color of a 
ceratopsian dinosaur. Naturwissenschaften Online Preprint, DOI 
10.1007/s00114-010-0661-3

  Abstract (it's a doozy):

  "Preserved skin of small dinosaurs is rare. Here, a specimen of the 
ceratopsian dinosaur, *Psittacosaurus,* presents some of the best preserved 
epidermal scales observed to date in a relatively small dinosaur, over wide 
areas extending from the head to the tail. We study the preserved epidermis of 
SMF R 4970, the different types of scales, color, and patterns, and their 
respective locations in the body. We use modern application of high-power 
digital imaging for close-up analysis of the tubercles and fragments of 
preserved color. Three types of scales are preserved, large plate-like scales, 
smaller polygonal scales or tubercles, and round pebble-like scales. The sizes 
of the plate-like scales vary in different parts of the body and vanish 
altogether posteriorly. Light and dark cryptic patterns are created by the 
associations of the tubercle and plate-like scales, and there is also evidence 
of countershading in the proximal caudal region, the body darker dorsally and 
lighter ventrally. Perhaps most impressive are the distinctive pigmented 
impressions of scales over most of the skeletal elements. The pigmentation 
follows the curvature of the bones implying that when it was deposited, the 
skin was still pliable and able to wrap around the visible parts of the 
elements. The present record of color is the first in a non-theropod dinosaur 
and only the second record in a non-avian dinosaur. Because of its resistance 
to degradation and ability to produce various color tones from yellows to 
blacks, we suggest that melanin was the dominant chemical involved in the 
coloration of *Psittacosaurus.* The data here enable us to reconstruct the 
colors of *Psittacosaurus* as predominantly black and amber/brown, in cryptic 
patterns, somewhat dull, but useful to a prey animal. Indeed, skin pigment 
within a partially degraded bone indicates that *Psittacosaurus* was scavenged 
shortly after death. The theropod dinosaur *Sinosauropteryx* has recently been 
reported to have naturally pigmented integumental structures, which th!
e authors
 as proof that they are protofeathers and not support fibers of collagen. Our 
findings in *Psittacosaurus,* on the other hand, indicate a more parsimonious 
and less profound alternative explanation, i.e., decomposition of the skin 
releases pigments that readily permeate underlying structures."

  One of the more fascinating aspects of this paper is the specimen, the famous 
"quilled" *Psittacosaurus,* which putatively incorporates detailed colors of 
patches of "skin" over various bones and between them. Just as fascinating is 
the expression of constant naysaying about how this material is preserved. TLS 
& Plodowski refer to the structures of color and scales as being "impressions," 
and leaving "traces" on the bones, but describe raised and detailed 
associations of structures quite distinct from both bone and the meaning of the 
word "impression;" these are, in fact, the carbonized remnants with their 
pigmentation intact of various integumental structures, as reported by the 
authors. How this doesn't apply to *Sinosauropteryx* (the shape of the 
structures being different means that the structures preserved there must NOT 
be supraintegumental, but subintegumental!

  The authors even claim that their work represents the first case of 
widespread integumental preservation inferring color in Liaoning, referring 
otherwise only to *Sinosauropteryx* but restricting its color to the tail. The 
authors reflect briefly on the possibility that the colors they discern are 
natural, referring instead to circumstantial data (e.g., countershading) to 
imply their frequent use of the term "color" is parsimonious. However, the 
authors cite Zhang et al., 2010 on the appearance of "color" in 
*Sinosauropteryx* (more on this below), but do not reflect on recovering 
melanosomes in their detailed microscopic photographs. It seems an oversight on 
two fronts: Zhang et al studied more than just *Sinosauropteryx,* and that the 
detail of the microscopic study fails to investigate melanosomes (largely due 
to not utilizing SEM on this specimen). 

  A comment at the end of the paper (the last paragraph, in fact) bears 
reiteration, as it extends from the discussion of apparently previously 
reported discussion of color in fossils from Liaoning (disputed by TLS & 
Plodowski):

  "Most recently, an SEM image on the theropod dinosaur, *Sinosauropteryx* 
(Zhang et al. 2010) from the Jehol biota purportedly shows the presence of 
melanosomes (see Lingham-Soliar and Glab (2010) for an alternative explanation) 
in the integumental structures of the tail, which the authors state is evidence 
that these structures were pigmented protofeathers and not support fibers of 
collagen (e.g., Lingham-Soliar et al. 2007). Our findings in *Psittacosaurus* 
on the other hand indicate a more parsimonious and less profound alternative 
explanation (accepting for the present that the structures identified were 
indeed melanosomes)–pigment in the integumental structures of *Sinosauropteryx* 
could easily have been absorbed from the overlying decomposing skin, a 
phenomenon amply demonstrated in the present study in *Psittacosaurus* SMF R 
4970, also from the Jehol biota."

  You will all note (as I do) that some aspects of this paragraph are 
troubling. First, TLS & Plodowski only mention *Sinosauropteryx*, while the 
study they cite also used *Sinornithosaurus*, *Confuciusornis*, and an isolated 
"avian" feather. Structures analyzed in that paper covered isolated areas of 
integument as well as regions overlying bone. Second, the authors are willing 
to accept the existence of melanosomes in other fossil specimens, and their 
relation to accurate preservation of supraintegumental structures, but instead 
decide that they would rather interpret them as decomposed remnants of degraded 
skin, overlying the subdermal collagen they have previously argued for.
                                          
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