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Re: altricial nestling bone fossilization



----- Original Message ----- 
From: "david peters" <davidrpeters@earthlink.net>
Sent: Thursday, October 14, 2004 1:15 AM

> Nope. It demonstrates nothing more than that you saw something and
> interpreted it as a pterosaur -- influenced by the fact that you know what
> pterosaurs normally look like. That the face on Mars looks like a face
while
> nobody expected one there isn't any evidence for its existence either.
>         I've never meant to say you were making it up. I'm just saying
that
> you desperately try to see _anything_ in the empty matrix, not necessarily
> anything _specific_. It's a Rorschach test.
>
> >>>> That can be true. Illusions do exist. So the bar must be raised and
some things that one sees cannot be accepted because they don't meet the
higher criteria. There are still a number of examples in which the baby
matches the mother in every detail except a short list of proportional
differences that are essentially constant across the Pterosauria.

That's still not enough.

> Some give insight into the mother that cannot be obtained directly, but
matches sister taxa. More importantly, in my desperation I should be seeing
babies everywhere. I don't. And believe me I look. Ratio of mothers to
non-mothers across 100+ taxa? About 30+%. Some taxa are entirely free of the
matrix, unfortunately.

This sounds better. Someone should test it, though.

> > The bottom line to my questioning is still this: which grows faster? A
> fully ossified bone eroding and redepositing itself? Or a softer sort of
> bone, held together by pterosaurs' unique 'Chinese handcuff/coaxial cable'
> woven -type ossification pattern, loose, poorly ossified and wonderfully
> expandable at first - increasingly dense and inflexible as maturity
> (puberty) arrives?
>
> The former.
>
> >>>>>> How can you compare one type of bone growth which is real, to one
that you claim is unreal?

Because I thought I had understood what you meant with that ossification
pattern. I hadn't. Could you explain what you mean? Just ordinary
fibrolamellar bone? Or are you alluding to the trabeculae inside a pneumatic
bone?

> But histologically pterosaur bones are unique in their structure.

You have the JVP article -- Padian, Horner & de Ricqlès, 24(3), right after
Jouve's -- that shows that the investigated pterosaur bones, at least, are
completely normal in their structure. All that's unique is the extreme
degree of pneumatization in the most derived clades. Or, see above, have I
misunderstood what you mean?

> How do you imagine an expandable bone? Twenty separate ossifications
> embedded in rapidly growing and slowly ossifying cartilage? Not only is
such
> a thing entirely unknown,
>
> >>>>actually the aftermath of that scenario can be seen histologically, in
fossilized adult pterosaurs.



> it also wouldn't have _any_ mechanical stability
> compared to the size of the animal, which couldn't stand on its legs, or
> cling to its mother without all its long non-bones bending rachitically.
>
> >>>> Think about it. In this scenario bending is okay. And maybe,
considering the stresses it would be under, selected for. The baby is only a
hitchhiker, not a walker. It seems to me, hypothetically speaking, the major
stresses on the bones -- not compensated for my the springy joints -- would
be compression and tension, as g-forces rule -- something coaxial cable and
Chinese handcuffs handle quite well without changing the volume of their
interiors drastically.

There we have it, compression and tension. The same as in standing and
climbing. The cartilages would be permanently deformed, and then they would
ossify in that deformed shape. Each and every pterosaur would be horribly
rachitic, and would never have learned to fly because its wings would have
been far too deformed. It just doesn't work. If you aren't just floating in
water and above a rather microscopic size, you need some sort of rigid
skeleton.
        Remember what cartilage is. Your ears have a cartilaginous skeleton.
See how pliable they are.
        Do you know what shark skeletons are made of? Of cartilage, yes, but
of _calcified_ cartilage. In mechanical terms, of de-facto bone. That's an
adaptation to the stresses of locomotion, which are smaller but more
sustained than those you experience if you wiggle side-to-side in bed.
(Assuming you don't lie on a side.)

> > What predators were climbing through the trees looking for babies in the
> Triassic? I'm not sure I can think of many, other than small lizards and
> that sort, some with gliding ribs.
>
> Drepanosaurids.
>
> >>>>> Prior to drepanosaurids this method seems to have arisen. And
drepanosaurids are in the club.

Müller's analysis, which includes prolacertiforms, finds them as the
sistergroup to the diapsid crown-group, which means they have a ghost
lineage that reaches back into the Permian. Not surprising for arboreal
animals.

(next post)
> PS:
>
> Of course, pterosaurs might have grown bones exactly like birds grow
> bones, via redeposition from embryo on up, but then there would still be
> that woven pattern that you see on pterosaur long bones left
> unexplained. However, if we attribute the weave to a unique method of
> bone growth and deposition, hypothetically speaking, of course, than no
> stones are left unturned.

I've read Padian et al., and I don't know what pattern you mean.

> And D. Marjanovic[...] still owes me/us some pterosaur baby + mama
> sketches or tight descriptions. Just throwing two genera into a ring is
> not good enough. I want museum numbers and parsimony.

Guilty as charged. I'd love to try some tracings on my own. The problem is
just that I don't have any pterosaur photos with a resolution that could be
taken seriously. I'd be very grateful if you could send me some.