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Re: altricial nestling bone fossilization

> I'm interested in rates and degrees of ossification in tetrapods that
enter this world essentially helpless. Unable to feed or defend themselves.

BTW, that's not what your newborn or even unborn pterosaur babies look like.
They look like they could even fly. They don't look like newly hatched
passeriforms that can barely lift their huge heads off the nest floor.

> And those that grow fast, within a few weeks or a season. Do their bones
show delayed ossification, perhaps because 'soft' bones grow faster than
hard ones do?

I'm not sure what you mean by delayed ossification. If you mean a later
_start_ of ossification, then no -- in all tetrapods ossification starts at
rather embryonic (as opposed to fetal) stages. If you mean a slower _speed_
of ossification, then yes -- even though nowhere near as dramatic as needed
to explain your pterosaur babies as unossified.
        Largely unossified bones would get deformed if they grew so fast.
(That's called rachitis when it does occur.) They do show woven bone
texture, though, and unossified articular ends (that's why they can't move
well). I'm sure you've read some popular explanations of *Maiasaura*
        I don't know if ducks qualify as precocial here... in any case, I've
got an impressive digital photo of a duckling's sterna plus one coracoid (I
don't know what precise age). The sterna are two flat plates, there's no
trace of an ossified keel, and the two bones aren't even sutured yet -- even
though the coracoid is completely ossified, and the facets for the sternal
ribs and the coracoids are fully formed in bone, too.

> What would also be intriguing is how long thin bones, such as heron or
flamingo tibiae and metatarsals grow.

I'll risk a guess: they start out short and stubby and then grow mainly in
length. Though not quite as impressive, our own extremities are a case of
just this happening.