RE: Troodon/Orodromeus hypothesis

[Jaime Headden <qi_leong@hotmail.com>]

Pardon the length of this post.

Let's summarize for those not following along.



  Claim 1. "[A]dult oviraptorids were eating hatchling *Byronosaurus*."

  Claim 2. "[Y]oung *Byronosaurus* left their nests and immediately tried to 
feed on oviraptorid hatchlings or eggs."

  Claim 3. "[A]dult Byronosaurus were nest parasites on oviraptorids."

Jason Brougham wrote:

<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.>

  Do note that nowhere do I declare that prismatoolithid eggshell or the 
"ootaxon" *Prismatoolithus levis* are extrapolatable across the entirety of 
*Troodontidae*. Just that *Prismatoolithus levis* was referred to *Troodon 
formosus*, where I not-jokingly coughed at the referral of skeletal and 
non-skeletal remains to a tooth-taxon, and that the prismatoolithid "oofamily" 
has been expanded across *Troodontidae* generally. I never said I agreed with 
this argument, nor did I say it settles the case I was arguing for.
 
<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.>

  You do not need to ask me twice, nor once, that I refrain from making broad 
assertions when I have made the same plea in the past. But note that it was my 
assertion that Bever and Norell HAD settled the issue, in that a broad reading 
would argue the authors assumed the eggshell was oviraptorid through and 
through; while Norell et al. HAD argued this strictly, and Bever and Norell 
referred to that work in remarking on the nests and egg identity, I figured it 
was sufficient; this is why I did not edit out the citations in the quote. I 
did make a mistake in affirming the quote saying what I argued, when it fact it 
did not (just assumed what I argued was already known, or inconsequential).
 
<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.>

To put my argument in context, although I wonder if a flow chart of this 
conversation would be so much better, I'll use another thing you write out of 
order here; I wrote:

<<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.>>

  <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?>

  First, I provided critique of three options you wrote for the association, 
one of which was troodontids feeding on the eggs, and the other being nest 
parasitism. In the first, I assumed you could be using the perinates and 
predators as well as adults, and argued primarily with the former premise in 
hand; I assumed the adults _could_ predate eggs and were likely to "partake" of 
the meal as opportunity arose. It would be a done deal, and a non-argument. In 
the second, though, applying juvenile predation on the nest would require the 
arguments I listed, and the reason for the quote. This was to help enforce the 
idea that I could reasonably preclude any and all juvenile predation on _eggs_ 
simply because of the size of the perinates. The only other option would be: 
Adult predation with juvenile exploitation, which is also entirely possible 
(there was no adult associated with the nest in question).

<No one has suggested that the preserved Ukhaa Tolgod eggs are Troodontid, have 
they? What doubt about association is there?>

  Note above where I refer back to the argument made about nest parasitism. I 
argued against this. How did you thin nest parasitism would occur? My first 
argument was that the eggshell was not troodontid, at least as far as 
*Prismatoolithus levis* implies troodontid eggshell, while the second was that 
oviraptorids are consistently elongatoolithid; since all the eggshell 
associated with the nest and embryos/perinates is apparently elongatoolithid, 
it is unlikely (not _actually_ -- I've been using "likelihood" modifiers all 
through this argument) that the perinates were occupants of the nest, rather 
than arrivals at it, or having been brought there.   
 
<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?>

More out of order stuff; I wrote:

<<Mere size alone prevents them from being predators of eggs; certainly the 
hatchlings, but the eggs, definitely 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.>

  Note now that the skull size issue is relevant. The "attendant predator" 
(nestlings joining in with mom/dad as predator) or "food" (food) options are 
equally likely initially, as no data seems to explicitly reject either, yet 
Norell et al. note both developmental concerns (the skulls do not seem to be of 
a precocial development, as they are unsutured and lose) while the skull size 
itself implies they could not have been good effective consumers of anything 
but the most delicate of foods. Mommy would have to be there to crack the eggs. 
Being unlikely (in my esteem) to be precocial, their presence at the nest 
implies they were "food" (food), rather than "attendants" (along for the ride).

  If you want a beer, say, at this year's SVP in Las Vegas, I'll get you one of 
your choice. I am not a betting man. But my argument does not make an absolute 
claim, it makes a likelihood claim. I've been continually stressing this 
_because_ of the unknowns involved. Getting a Djadokhta Formation troodontid 
egg would be very strongly useful in this discussion, and would likely settle 
the issue of what to make of the association of MPC 100/972 and 974 with 
oviraptorid eggs.
 
<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.>

  I'm not sure what the fourth claim is, I've been assessing the three listed 
above. Yes, the data can support all three. Lack of any supportive data on 
feeding prevents 1 from being directly refuted (no coprolite or similar 
"digested" remains, as the bones are not "etched" or abraded, crushed, etc.), 
and lack of evidence of non-elongatoolithid eggshell prevents 3 from being 
refuted; but I am fairly certain I have refuted 2, as it is unlikely the 
perinates could have broken eggshell thicker than their teeth that they 
themselves could fit inside, and how as no egg-eating animal isn't larger than 
the egg it seeks to consume.

  Specifically, you are correct that I cannot disprove that these particular 
troodontids were nest parasites, but there is similarly no evidence they 
_were_, just using that as a possible reason for the association. I'd like to 
know why specifically I should think of these perinates _as_ nest parasites, 
and what specifically you use to affirm this.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Ever since man first left his cave and met a stranger with a different 
language and a new way of looking at things, the human race has had a dream: to 
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