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RE: Troodon/Orodromeus hypothesis



Jason Brougham wrote:

  < This is an important point because the eggshell on the Byronosaurus could 
be troodontid eggshell if the mother Byronosaurus laid her eggs in the 
oviraptorid nest as a nest parasite. The byronosaurus specimens are perinates, 
meaning they could have hatched from their own eggs in the oviraptorid nest.>

  Very well, I'll give it to you that the text does not even imply that the 
eggshell adhering to the perinates was elongatoolithid.

  Let's assume that the eggshell is therefore unknown in provenance. We should 
not assume it _is_ oviraptorid, nor should be assume the shell is troodontid. 
We'll leave those options as equal results when asking the hypothetical of 
whether the eggshell associated with the troodontid skulls are troodontid. The 
first line of research is whether these eggs are of a dinosauroid-prismatic or 
a ornithoid-ratite morphology; the former indicates a similarity with 
*Prismatoolithus* from NA and associated with troodontid embryos, while the 
latter indicates *Elongatoolithus* (among others) and identical to the 
oviraptorid's "confirmed" eggshell (because of the embryo). One way to 
distinguish elongatoolithid eggs is by surface ornamentation, but another is by 
section; Norell et al. 1994 actually provides closeups of the work on the 
fragment of shell adhering to MPC [GIN (IGM)] 100/972 (fig.3f), so this is 
pretty easy to help answer this question.

  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. *Elongatoolithus*, on the other hand, 
especially the shells associated with the embryo, have surface ornamentation 
without reticulation, lumps, etc., but are extended into ridges ending in 
sometimes prominent tuberculae (this differs among species). So 
*Elongatoolithus* has ornamentation on its surface, *Prismatoolithus* does not.

  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.

  Compare now that figure. 
http://www.lowellcarhart.net/ebay/papers/a-theropod.pdf if you don't have a 
copy (easiest online version I could find not behind a paywall --- eBay?). The 
surface ornamentation is vermiform, not smooth. This implies the eggshell is 
elongatoolithid. Now, I'm gonna go the extra mile here and reiterate what I 
said earlier: it's _possible_ the troodontid is a nest parasite. Of course, 
maybe not all troodontids have the same eggshell type. Maybe some troodontids 
had elongatoolithid eggshell type. But this is a likelihood game, and I find 
that to be rather far-fetched without actual data to show any variation, for as 
a comparison to troodontid-eggshell-variation, it should be noted that all 
different oviraptorid taxa associated with nests (*Oviraptor philoceratops*, 
*Citipati osmolskae* and that thing from the Wulansuhai Formation [Bayan 
Mandahu]; see Dong and Currie, 1994) all have elongatoolithid eggs. By 
extension, _all troodontid eggs should be prismatoolithid_. It's a hypothetical 
extension, but a useful one as it permits predictions and can be falsified.

  So the eggshell is probably opiraptorid in orgin.

 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.

In another post:

  <I'm not suggesting that hatchling troodontids could do this successfully.>

  Good, because the idea of an animal trying to hurl the eggs to crack stones 
against the eggs, which are larger than themselves in volume, seems a tad 
silly. 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.

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 kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)





----------------------------------------
> Date: Sat, 14 May 2011 18:23:02 -0400
> From: jaseb@amnh.org
> To: mjohn.bois@gmail.com
> CC: dinosaur@usc.edu
> Subject: Re: Troodon/Orodromeus hypothesis
>
>
>
>
> John Bois wrote:
>
> > Yes...
> > And Rhea eggs are destroyed by diminutive hairy armadillos. To my
> > knowledge no one has observed how they do it...the presumption is that
> > they knock the eggs together!
> >
>
> Amazing. I've found films online today showing vultures breaking ostrich
> eggs by hurling stones into them, and Australian Eagles breaking emu eggs
> the same way.I'm not suggesting that hatchling troodontids could do this
> successfully.
>
> I've also watched films today of jackals gnawing on ostrich eggs and
> failing to break them. I bet that is a more likely scenario for small
> troodontids.
>
>
> Jason Brougham
> Senior Principal Preparator
> Department of Exhibition
> American Museum of Natural History
> 81st Street at Central Park West
> 212 496 3544
> jaseb@amnh.org
>