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Re: altricial nestling bone fossilization



I would be asking a different question, one perhaps not so loaded towards
altriciality or otherwise:

  "What is the effect of age on bone permineralization?"

  One can then step into the effects of altricial versus non-altricial
animal bones and how they would be preserved. I don't think modern studies
have addressed this topic. I know of someone who is trying to practically
test methods by which soft-bodied animals are preserved, but not bone, as
yet.

Trueman, C. N., and D. M. Martill. 2002. The long?term survival of bone:
the role of bioerosion. _Archaeometry_ 44(3):371-382.

Abstract:
  "Fossil bones (N = 350) spanning more than 350 million years, and
   covering a wide range of depositional environments, were studied to
   compare the distribution of microbial destruction features in fossil
   bones with previously published data sets of bones of archaeological
   age. The distribution of bioerosion in fossil bones is very different
   from that found in bone from archaeological sites. Fossil bones
   typically show little or no bioerosion. Under normal conditions, if a
   bone is to survive into the fossil record, then rapid bioerosion must
be
   prevented (or halted). This conclusion suggests that early post mortem
   processes, such as the mode of death, influence the potential of any
   bone to survive into deep time."

  In other words, age may not really matter at all, as it seems
preservation of bone is really a matter of not being damaged biotically
(in some cases, age may be a null factor: around 1/5 of dinosaur fossils
known to date are based on juvenile or subadult animals; in several cases,
juveniles may be better represented for some species than adults, by
factors of preservation, like the difference between the juvenile
*Scipionyx* -- so well preserved there are internal bones and a patina on
the bone that is generally absent from lagerstätt-preserved fossils -- and
the German "adult" and closely-related *Compsognathus* in which this
patina and degree of preservation is lacking and bone is cracked, eroded,
and degrading so that very few natural margins are present in the
postcrania).

  It would perhaps serve well to those who would hold that precocial or
altricial animals don't NEED ossified skeletons to actually TEST their
statements. Even in human altricial young, ossification occurs in the bone
plates and most long bones, though not in the ends of bones, that given
structural integrity to loading forces, including those that effect bone
movement (e.g., crawling) where attempts to move against ground force are
most important. There are reasons for the need to develop bone formation
_quickly_ and humans AND birds do this very quickly, as opposed to
extended duration of a semi-embryonic state post-natally, as in
marsupials.

  Check out the following, for instance:
http://www.stanfordalumni.org/birdsite/text/essays/Precocial_and_Altricial.html

  I personally would like to see some demonstrative work on bone formation
or lack thereof in juvenile organisms before conclusions based on
single-person observations are explained as examples of such.
Developmental biology, and indeed, in keeping with evolutionary biology
for the developmental biological evolution synthesis, has held for some
time that bone formation in unsupported young (animals clinging to their
mothers are NOT "unsupported").

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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