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Re: Herrerasaurus skin?



Ralph W. Miller III wrote-

> _Pelicanimimus_ "skin" impressions were apparently subcutaneous muscle
> tissue, which tells us nothing about its exterior appearance except that I
> recall that the specimen apparently displays evidence for a dewlap under
the
> chin;

Actually, some skin is preserved in Pelecanimimus.  It's present on at least
the throat pouch, but Briggs et al. (1997) are not very specific regarding
which areas preserve skin, which preserve muscle and which are just outlines
of microbial mats.

"These occur in the throat region, flanking the more proximal neck
vertebrae, in the vicinity of the ribs, and behind the elbow. In addition a
small triangular area at the rear of the skull was interpreted as a possible
occipital crest. Analyses confirm that these features represent mineralized
traces of soft tissues. They are preserved both as replicas of the original
skin and muscle tissue, and as impressions on microbial mats or veils that
grew over them."
"In some places, such as the region under the throat, muscle tissues retain
some three-dimensional detail, including the sarcolemma.  They have been
replaced in an iron carbonate. A distinct cross-hatched patterning on the
surface of this material represents wrinkling of the hide of the dinosaur.
The surface of the skin is smooth and lacks any visible dermal structures
(e.g. feathers, scales, hair)."
"Elsewhere the soft tissues of Pelecanimimus are preserved by the outline of
phosphatized microbial mats that overgrew the carcass. These mats consist
mainly of thin layers of coccoids embedded in a film that may represent
mucopoly-saccharide sheaths surrounding the cells (i.e. a glycocalyx). Where
the margin of these white phosphatized mats forms a well defined line it is
assumed that this represents the outline of the dinosaur. Closely spaced
lineations running parallel to the bones are the result of micron-scale
cracking of the mats. The mats also display polygonal cracking presumably
due to shrinkage associated with the mineralization."
"Our analysis confirms the existence of either a throat pouch or dewlap, and
soft occipital crest in Pelecanimimus, and demonstrates the importance of
microbial mats in preserving such details."

Mickey Mortimer