[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Bird/hibernation/torpor

Jim Kirkland, your post gave me the enjoyable task of re-reading your
_Dinosaur Eggs and Babies_ paper.  I agree with practically everything in
it but I would make the following comments regarding your post as
it relates to your paper and my own ideas.

     You say that dinosaurs were able to withstand millions of
years of egg predation and ask, in different words: What, then,
could have changed towards the K/T to cause extinction via this

     I claim new mammal and bird species may have had an
influence here.  

You say: "Although both _Gobiconodon_ and _Didelphodon_ were
large enough (cat-size) and physically capable of eating dinosaur
eggs, there is no evidence of this having taken place."  And
Betty Cunningham also wonders why we have found no such
associations if they indeed occurred.  Are the following good

1. Mammals are smarter and generally more behaviorally talented
(gestation and lactation allows the development of a relatively
bigger brain).  They don't get caught as easily as reptilian egg
thieves.  In (I think) three years of observation of ostrich egg
predation, Bertram (ref. if needed) did not find one instance of
penalty against thieves.  This was because the damage was done
either when the ferocious ostriches were absent (by Egytptian
vultures) or at night when the Os seem to have no response to
animals such as jackals and hyenas (the former would never try
this in the day time).

2. Mammal nest attack (if it happened) might have occurred in a
relatively narrow evolutionary time period.  This lowers the
likelihood of any being found.

3. I think mammal bones don't fossilize as well as dinosaur

By the way, I once read of Andrew's expedition that they pulled
(Zalambdalestes?) skulls out of dino nest beds (protoceratops?). 
Has anything more been said about that?

4. We haven't yet found all mammalian contenders.  

You say: "Because most, if not all, dinosaurs, probably buried
their eggs to at least some degree...raiders of dinosaur nests
would have to have the ability to dig open the nest.  Such an
ability is unlikely for most...birds."

First of all, I think it likely that birds took a terrible toll
on hatchlings.  Like Marshall eagles which today snatch ostrich
chicks from under their parents' beaks, pre K/T birds may have
decimated dino babies.  This claim is bolstered by recent
molecular clock evidence using the "quartet" method for
calibration (is there consensus that this is reliable, I'm not
sure).  Anyhow, this states that all modern birds had a common
ancestor way back 98 mya.  This leaves plenty of time for the
development of _Falconiforms_.  There is also a likelihood that
F. analogues in the enantiornithines existed.

     But to argue your point directly, I have seen crows exposing
sand covered eggs (eggs that I have covered).  They do it by
flicking their beak.  I have also seen them rifling through trash
throwing chunks of this and that unceremoniously around the
place.  And why not some chicken scratching bird?

     These claims are criticized on the basis of lack of hard
evidence.  But, as you know, there is _no_ direct evidence of egg
predation of any kind (I think).  And yet there is no doubt that
it existed at some frequency.  I'm not sure I could say why
people are comfortable with the statement: "egg predation
occurred", and not with: "mammals and birds preyed on dinosaur
eggs and babies".  Are these statements qualitatively different?

You say: "There was ground cover at many Mesozoic sites as
indicated by densely and finely rooted paleosoils.  In many cases
it was ferns."

But ferns have flagellated sperm and require water to reproduce. 
They are (today, anyway) usually restricted to damp environments. 
Faunal density is higher in these environments.  This is not
analogous to desert margins and savannah.  My point is that
grasses provide cover in areas that were inaccessible to mesozoic
plants.  In so doing they allow refugia to dry-tolerant big egg
layers where predator densities are low.  This allowed ostriches
a means to escape extinction that was unavailable to non-avian