Re: archie feathers

[Colin McHenry <cmchenry@westserv.net.au>]

----- Original Message ----- 
From: "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>

> Actually, no: there are yet more possibilities:
> *Ontogenetic variation (after all, the feather IS smaller than the
retrices
> and remiges of the Archies with good feather impressions)
> *Seasonal variation (although in modern avialians, such changes are
> predominantly color-related)
> *Taphonomic variation: the lone feather, after all, is preserved via
> carbonization, while the others are through impressions. Furthermore, any
> 2-dimensional (or nearly 2-D) representation is a 3-D object suffers from
> distortions; the same object might produce one of several different forms
> when projected onto a 2-D surface.

Is the possibility that the isolated feather is a detached down or contour
feather included in these?  Paul Davis (1995)states that these feathers
become detached from the carcass before the flight feathers (alluding to a
system of decay stages that he details in a later publication - Davis &
Briggs 1998).  Are there down or contour feathers preserved on any of the
_Archaeopteryx_ specimens for comparison?  My impression has always been
that the specimens show the impressions of the flight feathers only.

He also states that the _Compsognathus_ specimen from the Solnhofen "may for
all taphonomic intents and purposes be treated as a small featherless bird"
[p91].  The implication is that, if small dinosaurs like _Compsognathus_
were feathered (as was its close relative _Sinosauropteryx_), why are there
no feathers preserved on the Solnhofen _Compsognathus_, despite the famous
frequent preservation of feathers in the limestone?  He doesn't specify what
stage of decomposition the specimen is at, but it would seem possible that
the specimen was preserved at a stage of decomposition after the loss of the
integumentary structures.  In which case, if it is not a down or contour
feather from _Archaeopteryx_, then might the lone feather be from
_Compsognathus_?

The Solnhofen _Compsognathus_ has been interpreted as an animal that died on
land and which was swept into the lagoon by flood water.  However long it
had been dead, the skin - or at least the peritoneal cavity - was not
breached before deposition, as evidence by the lizard in the stomach.
Judging from the articulation of the specimen, Davis estimates that the
animal had been dead for a short time - 1 to 3 days - before burial.  This
doesn't seem like enough time to lose whatever feathers might have been
present, however downy they might be.  However, Davis seems to have based
his estimates of decay time on experiment work that monitored decay of
submerged carcasses (published in the 1998 paper).  In contrast, the land
near the lagoon has been described as being semi-arid (Barthel et al 1990,
quoted in Davis 1995).  Based upon my own observations of carcasses in semi
arid regions, it seems possible for a small animal to be dead for quite some
time before the integument is disrupted, as long as it is not disturbed by
scavengers.  This may provide the opportunity for loosely attached
integumentary structures to become detached before the integument is
disrupted.

Cheers
Colin



Colin McHenry
Geology Building
University of Newcastle
Callaghan  NSW 2308
Australia

Tel +61 2  4921 5404 (work)
      +61 2  4997 1038 (home)
            0428 131 858 (mobile)

cmchenry@westserv.net.au