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re: altricial nestlings, PS



An explanation for "woven" bone texture:

  "Woven" bone texture is expected for all tetrapod neonates, as this is
the matrix for collagen and calcite formation of mature bone, prior to the
development of the periosteum. Woven bone texture has been noted in
crocodilians, birds, frogs, salamanders, fish, and even mammals. This is
thus a constraint for other animals that may NOT preserved an ontogenetic
condition in which woven bone occurs. Progression from a cartilagenous
stage (almost entirely embryonic) into a calcite deposition stage over
bone collagen (late embryogenesis, neonates, hatchlings, marsupial young,
etc.) and into a development of juvenile perisoteal cartilage and bone
(finished bone) in placental young, birds, crocs, and so forth, has been
extablished for some 300 years. It is unlikely, without an embryonic
series to account for the bone textures and ossification centers during
embryogenesis into maturity, that any other pattern has ever occured, or
that such bone texture represents _adult_ conditions (as in his hypothesis
regarding *Avgodectes*). Furthermore, there is not a tetrapod alive that
shows ossification of long bones from more than two or three centres of
formation, including the core of the long bone, and both epiphyseal
centres. Birds, crocs, and other reptiles, do not have such a condition,
but ossify from the center of the shaft distally.

  Something I should have brought up a while back, instead of living in a
theropod-centric world with the lovely new dinosaurs being described in
_Nature_ this October:

  There is a wonderful story regarding the taxonomy of Lambeosaurinae
species, most especially those ascribed to the taxa *Chenosaurus* and
*Procheneosaurus.* Without taking bone texture into account, they have
been split up and multiple age-related species have been allometrically
"sorted," resulting in the "collapse" of *Corythosaurus* and
*Lambeosaurus* species along with *Procheneosaurus* and *Cheneosaurus*
into what are now regarded as the modern synthesis: *Corythosaurus* used
to have something like 10 species, now it has 1, all species being size
and crest-shaped variants, much as has been noted for cassowaries of the
same species; *Lambeosaurus* may only represent up to three species,
instead of something like 6, but only two of these were based on any form
of cranial material; *Procheneosaurus* and *Cheneosaurus* are, for the
most part, not considered obsolete collections of polyphyletic non-adult
specimens of *Corythosaurus,* *Lambeosaurus,* and *Hypacrosaurus.* As
recent work has shown by the efforts of Dodson, Ostrom, Chapman,
Brett-Surman, Godefroit and many others, these taxa are NOT synonymous at
the "genus" level, but show widely divergent clines of parallel evolution
of their various cranial ornaments.

  Bone texture has been a major catalyst in new work sorting out juveniles
and adults from one another, and helped demonstrate synonyms among
arthrodires, salamanders, *Eusthenopteron,* primitive morganucodontid
mammaliaforms, and so forth, and has been supported by the modern
embryonic literature, even applied to crocs and birds. There is no reason
to doubt this utility. Because of this, and not bringing up the OTHER
reasons, Dave Peters' theory that *Avgodectes* is more mature than a
embryo or neonate is false. This does not mean that the artifacts being
seen in sediment are false, but at least as far as the Wang and Zhou
specimen goes, they were right to begin with.

  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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