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At 11:33 AM 10/30/96 -0700, Jeff Martz wrote:

>> Compsognathus-grade coelurosaurs are not particularly close to the origin of
>> birds: more so than Carnosauria, for example, but less so than
>> dromaeosaurids, oviraptorosaurs, etc.
>     When the discussion about Velocirpator patagiums was going on, who 
>mentioned the juvinile dromeosaur skin impressions?  Do those show scales 
>or smooth skin?

I do not remember.  I have not seen this specimen, either in person or in print.

>    If _Paleocanimimus_'s features are really homologous with feathers, 
>it could seriously screw up my "T.rex young din't have feathers" argument. 

Indeed.  And, the name is _Pelecanimimus_ ("pelecan" is Latin for pelican).

>> There are no good specimens of ornithischians, sauropodomorphs, ceratosaurs,
>> "megalosaurs", or carnosaurs found in such fine-grained sediments.  These
>> are all fairly big animals; not the sort of critter normally found in
>> lithographic limestones of any age.
>    Again, does the sediment really have to be especially more fine grained 
>then sediments that can retain skin impressions?

Oh, my, yes!!  It looks as if only the most fine-grained sediments
(lithographic limestones) can preserve feather impressions, whereas almost
any mudstone or fine grained sandstone (much coarser rocks) can preserve
skin impressions.

>If sediment is fine grained enough that you can press skin into it
>and leave an impression, why can't you do the same with feathers?

Because only the most fine-grained of sediments can preserve the details of
feathers.  Any sediment that preserves feather impressions can probably
preserve skin impressions, but not vice versa.

(Similarly, the record of wing impressions of pterosaurs are similarly
restricted to lithographic limestones.  Even the relatively fine-grained
Niobrara Chalk does not preserve wing impressions of Pteranodon, whereas the
Solnhofen Lithographic Limestone is noted for excellent impressions of
Rhamphorhynchus, Pterodactylus, etc. wings).

> What sort of sediment do the _Paleocanimimus_ impressions come from?

The Las Hoyas is a lithographic limestone, similar to the Solnhofen.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"There are some who call me...  Tim."
-- Tim the Enchanter, "Monty Python and the Holy Grail"
---------- subtitle --[Monty Python ik den Holy Grailen]

"Tim?!?  They called me TIM?!?!"
-- Tom the Paleontologist, on seeing "The Ultimate Guide to T. rex" :-)