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RE: Troodon/Orodromeus hypothesis



Jaime,

Thanks for the correction. As you write, it was Norell et al. 1994, not
Bever, Norell 2009, where they mentioned the convex surface of the
eggshell.
I also missed that Figure 3F is eggshell from one of the Byronosaurus
skulls. Odd, then, that the authors did not explicitly suggest that the
eggshell is oviraptorid.

I agree that it is most parsimonious to assume that a character state seen
in one sample from a clade is the same throughout the clade. Thus, all
troodontids can be assumed to build nests and to have prismatoolithid
eggshell. However we both know that, as sample sizes have increased, the
distribution of many characters across maniraptora has turned out to be a
bewildering thicket of convergence, reversals, and mosaic evolution (I'm
thinking of pygostyles in oviraptorids and avialae, edentulous beaks in
Confuciusornis and neornithes but not in basal ornithurines, unfused pubic
symphyses and carinate sterna in alvarezsaurs, etc). I feel that you
should also be cautious in making categorical statements about Troodontid
eggs being unornamented, since Grellet-Tinner and Chiappe (2004) reported
ornamentation in Troodon eggshell. I think that Jackson (2009) cleared
that matter up, that it was a misinterpretation of the terminology by the
former authors, and you and I agree that no published sample of Troodon
eggshell is ornamented in the strict sense. But we also both know that
Troodon is just one species in a speciose, diverse, clade that persisted
from the Jurassic until the end of the Cretaceous.

I renew my suggestion that all of us on the dml, including me, refrain
from making categorical statements based on a priori reasoning. In other
words I fear that, if we relied on armchair logic, we could spend weeks
vehemently debating whether it is anatomically possible for a snake can
swallow an egg bigger than its own head. But if we had simply consulted
the literature we would have quickly settled the matter and learned that
the answer is that they can and do.

In the case of Byronosaurus chicks attempting to prey on oviraptorid eggs
no one has suggested that they could crack the eggshell by biting it. And
we all agree that it is silly to imagine paravians cracking huge eggs by
flinging rocks at them. However, it is also silly looking when adult
vultures and eagles actually do it successfully. It is also silly -
looking when a stoat rolls a kiwi egg down a hill until it hits a rock and
cracks open. Silliness, therefore, should not be our measure of truth. I
wish there were extant, precocial, predatory birds, preferably flightless
ones, so we could observe whether those hatchlings are attracted to nest
sites.

Perhaps we can all agree that all manner of small predators are attracted
to the nests and eggs of larger animals (hairy armadillos, stoats, rats,
opossums, etc) whether or not they can successfully predate the eggs
therein. Perhaps the body or the droppings of the brooding oviraptorid
even attracted insects? Flies certainly are attracted to any large animal
in the Gobi today. I think it is entirely plausible that precocial
Byronosaurus chicks dispersing into the bleak Djadohkta landscape could
have investigated an oviraptorid nest long enough to get killed by the
parent oviraptorosaur and/or to be fossilized there in a sand flow.

Bever and Norell (2009, pg. 3) described the fossil nest from the Xanadu
locality  as containing at least six eggs. I have never suggested that any
of those eggs are troodontid, and I don't think anyone else did either.
However, in Norell et al 1994, one of the Byronosaurus skulls is described
as being found in a nodule lying 3cm from the oviraptorid egg. It is
perfectly plausible that this small nodule represents a fragment of a
troodontid egg, though the authors concluded and I agree that the evidence
does not support this possibility.
Jain=me Headden wrote:

>   First, the surface texture of *Prismatoolithus levis* (referred to by
association with troodontid embryos to *Troodon formosus* -- COUGH) is
absent: There is none. Smooth as a baby's bottom.

I agree with you, but Grellet-Tinner and Chiappe do not agree with you and I.


>   Second, the eggs of the troodontid clutches from Montana are generally
laid out in a pattern somewhat different from those of nests at Ukhaa
Tolgod, where the eggs are mostly vertical rather than horizontal. While
this doesn't stop some birds from ignoring that one of their eggs looks
funny, or that they are dealing with an egg half their own body size or
larger, or -- DAMN that chick is as big as mommy! -- it's interesting
that
> such a discrepancy raises doubt about association.

I don't follow you. No one has suggested that the preserved Ukhaa Tolgod
eggs are Troodontid, have they? What doubt about association is there?

>  Then there's this, from Norell et al.:
>
>   "Although these skulls are slightly longer than the skull of the
oviraptorid embryo, when the relatively short length of oviraptorid
skulls
> is taken into account they are quite similar in length. The outer
surface
> of the eggshell adhering to one of the dromaeosaurid skulls is in
contact
> with the skull, which indicates that the skull was not enclosed by that
particular egg." [pg. 781]
>
>   This is why the skulls are called "perinate," as they cannot be
reasonably said to be hatchling or prenatal, but there would have been
almost no difference in size. So these guys are the very age they would
need to be to be hatchlings or embryos torn forcefully from the egg.
Nonetheless, the lack of any indication of the latter implies the
perinates were _not_ in eggs at the nest. I would thus discount the idea
that the perinates are the product of nest parasites. But again, this is
just a "likelihood" game.

The first sentence offers little useful information and could be written
more clearly. I am disappointed that you cited it. The skulls are the size
they need to be to: 1) have been predated by an ovirpatorid in their eggs
2) have been predated during or just after hatching 3) have been still
within their own eggs in a host nest 4)  have been hatching or recently
hatched in a host nest. What we need is evidence that makes one of the
four more or less likely, not evidence that supports all four equally,
don't you agree?

In contrast, the second sentence is an excellent choice. It (weakly)
contradicts possibility 3. Therefore it does accomplish something, it
makes possibility 1, 2 and 4 the most likely (and they are equally likely)
of the four hypotheses. Please remember that 4 involves nest parasitism.


>  Mere size alone prevents them from being predators of eggs; certainly
the hatchlings, but the eggs, definately not. Maybe they were waiting
around for the eggs to hatch, then BAMM! free lunch. Hmmm. What about
adult troodontids eating eggs? Well, that's where dentition gets
ya.

That's the sort of language I encourage you to reconsider. If we were
betting men, and I could find even one documented case of a small animal
opening a big egg, you could wind up owing me a beer.

No one has suggested the troodontids would wait patiently for an egg to
hatch. We know that small predators investigate nests with eggs in them,
it is not far - fetched.