Re: Preservational bias revisited

[John Bois <jbois@umd5.umd.edu>]

On Mon, 16 Jun 1997 jamolnar@juno.com wrote:
> The rate
> varies from very quickly in a rain forest to leisurely in a northern
> woodland, but the recycling happens.  This makes for lousy preservation,
> unless it gets so acidic it becomes bog-like and suppresses the
> decomposing bacteria.

If memory serves, one of the points from the earlier thread on
preservational bias was that occassionally there are events such as ash
falls , etc. which nevertheless inter forest dinosaurs.  So why not any
eggs which may have been present?  I understand that this is a rare
occurrence but why not _any_?
        Also, on e would think that forested riparian environments might have 
been
subjected to preserving deposition.   I'm just now reading Horner's
_Digging Dinosaurs_.  He describes an island surrounded by trees, but the
nests are in the clear, not among the cover!  They would have been
preserved, though, if they were in the cover.

> 3) The ground in a wooded area is not easy to mound up or dig into, due
> to the dense packing of roots from forbs, shrubs, ferns and trees.  The
> mound-like nests found for dinosaurs so far are easier to build from
> other (drier sedimentary?) materials.  This is not to say that dinosaurs
> couldn't take mud from a forested riverbank or stream and build up a
> mounded nest in the woods,...


How would they move it.  Some of those nests have quite a large volume of
nest material?

> ...but most mud under those circumstances would  have a lot of organic
> matter in it, and therefore be more likely to
> decompose after use.  Just as in birds, dinosaurs would not reuse a nest
> the next season, or the parasite load would get intolerable.

Horner believes some dinosaurs at least revisited nest sites year after
year.

> 4) If dinosaurs in woodlands were more secretive, due to a larger
> diversity of potential predators being present, they might choose to nest
> in hollow logs or tree bases, or even dig a den of some sort.  Those
> types of nests are not easily preserved either.

Again, if memory serves, dinosaurs were unlikely to be den diggers due to
morphology.  Also, mammals, lizards, and, toward the end of the cretaceous
at least, snakes may have made laying eggs in hollow logs and tree bases
rather difficult.  I know I asked a general question but, to focus on the
late cretaceous for a minute, there were no really small dinosaurs
(actually, if one argues that there _were_ close-cover nests but they have
been simply obliterated by some of the forces you mention, couldn't one
also argue that there were small close-cover dinos which suffered the same
fate), chicken-sized and above would be less likely to lay in these micro
nesting sites--or am I wrong about that?