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RE: Wrong Reconstructions
Jason Brougham wrote:
<1) as far as rotating, do you dispute the conclusions of Varricchio et
al. that the eggs being half - buried in sediment indicates that they
were not rotated, and his speculation that the chalazae (which allow
bird eggs to survive rotation, while those of crocodiles cannot)
probably evolved further up the cladogram, closer to the Avialae?>
I am not referring to rotation of eggs, I am referring to a laying animal
squatting, laying eggs, then turning slightly, laying more, turning slightly,
then laying more, until completing a circle. This results in a concentric ring
of eggs with an empty spot in the middle (Clark et al. 1999).
Clark, J. M., Norell, M. A. & Chiappe, L. M. 1999. An oviraptorid skeleton
from the Late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avianlike
brooding position over an oviraptorid nest. American Museum Novitates 3265:1-36.
<2) Are you sure that the confusion about nest makers isn't the opposite
of what you've written? I know that Horner assigned a clutch of 19 eggs,
MOR 246, to Orodromeus, and that Varricchio reassigned it to Troodon
when further preparation showed Troodontid synapomorphies in the embryos
within the eggs. What specimen numbers are now "considered to belong to
Orodromeus" that were formerly assigned to Troodon?>
So far, the only referrences I note are the following, and they appear to
indicate that I was wrong in arguing that Varricchio was discussing *Orodromeus
makelai* eggs, rather than some random troodontid.
Horner, J. R. 1984 The nesting behavior of dinosaurs. Scientific American
Varricchio, D. J., Jackson, F. D., Borkowski, J. J. & Horner, J. R. 1997. Nest
and egg clutches of the dinosaur Troodon formosus and the evolution of avian
reproductive traits. Nature 385:247-250
Varricchio, D. J., Horner, J. J. & Jackson, F. D. 2002. Embryos and eggs for
the Cretaceous theropod dinosaur Troodon formosus. Journal of Vertebrate
Varricchio, D. J., Moore, J. R., Erickson, G. M., Norell, M. A., Jackson, F. D.
& Borkowski, J. J. 2008. Avian paternal care had dinosaur origin. Science
In my defense of my argument, however:
In the last paper, the conclusion afforded to male-avian parental care
(male-exclusive-brooding, above) was one of four options in the graphing
logging clutch volume to brooder's mass, with the sampled nests/brooders also
clustering with female-exclusive-brooding among crocodilians (where the
clustering for the former contains the sampled nests largely in one small
section of the overall distribution, while most of the MEBs assessed where
elsewhere in the graph; in FEB crocodilians, the samples occur along the
perimeter of the clustering but that clustering is more exclusive to the region
of the grapoh than it is in MEBs, implying a greater average and mean to
position than in MEBs). It should be noted that the authors use secondary lines
of data, including hyperprecocialism and simultaneous timing of hatching, but
both of these occur in crocs (as noted by the authors) and ducks (also, noted
by the authors) which are female-exclusive-brooders and pair-bond brooders,
respectively (if I contain my example to wood ducks, I'll be even better off in
this example). This implies the authors are focusing on the absence of
medullary bone to weigh the data, for which a single troodontid specimen and a
single specimen of *Citipati osmolskae* are exemplars of. Multiple brooding
oviraptorids are known, one of which is from Bayan Mandahu (Dong and Currie,
1996) and has a good chance of not being *Citipati osmolskae* to increase the
potential taxonomic sampling.
Dong Z.-m. & Currie, P. J. 1996. On the discovery of an oviraptorid skeleton on
a nest of eggs at Bayan Mandahu, Inner Mongolia, People's Republic of China.
Canadian Journal of Earth Sciences -- Revue canadienne de Sciences de la Terre
Sampling only two oviraptorids, while sampling animals on orders of
several magnitudes larger than any living nesting animal much less birds
(*Allosaurus*, Erickson et al., 2007 -- important as clutches are
unknown), impairs the sample value of the data set, while the extant
sampling is comprehensive enough to distribute the taxa into ambiguous
Erickson, G. M., Curry Rogers, K., Varricchio, D. J., Norell, M. A. & Xu X.
2007. Growth patterns in brooding dinosaurs reveals the timing of sexual
maturity in non-avian dinosaurs and genesis of the avian condition. Biology
Letters (Royal Society) 3:558-561.
Jaime A. Headden
The Bite Stuff (site v2)
"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
> Subject: Re: Wrong Reconstructions
> From: firstname.lastname@example.org
> Date: Fri, 28 Jan 2011 18:33:32 -0500
> CC: email@example.com
> To: firstname.lastname@example.org
> On this paragraph:
> > The nests Varricchio is referring to are similar to those of *Citipati
> > osmolskae* in forming concentric rows of stacked eggs set in pairs around a
> > common center; this laying pattern is consistent with a single female
> > laying, rotating, laying, rotating, etc. and not consistent with multiple
> > females laying in a common clutch. At least some older papers referred
> > nests now considered to belong to *Orodromeus makelai* to "troodontids,"
> > showing a less organized, erratic clutch pattern similar to that advocated
> > by Varricchio of "Troodon" in the Two Medicine.
> I have two questions.
> 1) as far as rotating, do you dispute the conclusions of Varricchio et al.
> that the eggs being half - buried in sediment indicates that they were not
> rotated, and his speculation that the chalazae (which allow bird eggs to
> survive rotation, while those of crocodiles cannot) probably evolved further
> up the cladogram, closer to the Avialae?
> Thanks again.