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Re: Paired Eggs in a Dinosaur Indicate Biological Sex



Jeff Hecht (jeff@jeffhecht.com) wrote:

<At least one of the paleontologists I talked with recently was not convinced
those were eggs in Sinosauropteryx. (Sorry, but I can't remember who because I
was working on a big project and talked to a lot of people.) It was not that he
could prove they weren't eggs, but that there wasn't enough evidence to prove
that there WERE eggs. They do not preserve shell. The new fossil does preserve
shell, with features which match known fossil eggs, so there's no doubt what
they were and good evidence they were about ready to be laid.>

  Well, to Chen Pei-Ji's credit, here's what has been said previously:

  "Low in the abdomen of NIGP 127587, anterior to and slightly above the pubic
   boot, lies a pair of small eggs (37 X 26mm) (Fig. 4a,c), one in front of the
   other. Additional eggs may lie underneath. Gastralia lie over the exposed
   surfaces of the eggs, and the left femur protrudes from beneath them, so
   there can be no doubt that they were within the body cavity. It is possible
   that the eggs were eaten by the dinosaur. However, given their position in
   the abdomen behind and below the stomach contents, and the fact that they
are
   in the wrong part of the body cavity for the egg shell to be intact, it is
   more likely that these were unlaid eggs of the compsognathid. Eggs have also
   been reported in the holotype of *Compsognathus* [see ref 19], but they are
   more numerous and are only 10mm in diameter. As they were also found outside
   the body cavity, their identification as *Compsognathus* eggs has not been
   widely accepted. The presence of fewer but larger eggs in *Sinosauropteryx*
   casts additional doubt on this identification.
  "Although more than two eggs may have been present in the larger specimen of
   *Sinosauropteryx*, it does not seem as though many could have been held
   within the abdomen. It may well be that these dinosaurs laid fewer eggs than
   most (some species are known to have produced in excess of 40) [see ref 20].
   However, it is more likely that their presence demonstrates paired
ovulation,
   as has been suggested for *Oviraptor* [see ref 21], *Troodon* [see ref 22]
   and other theropods. *Sinosauropteryx* therefore probably laid eggs in
pairs,
   with a delay for ovulation between each pair."

  -- from Chen P.-J., Dong Z.-M., and Zhen S.-N. 1998. An exceptionally
     well-preserved theropod dinosaur from the Yixian Formation of China.
     _Nature_ 391: 147-152.

  "Low in the abdomen of NIGP 127587, anterior to and slightly above the pubic
   boot, lies a pair of what appear to be small eggs (Chen et al. 1998).
   Gastralia lie over the exposed surfaces of the eggs, and the left femur
   protrudes from beneath them, so there can be no doubt that they were within
   the body cavity. These oval structures (37 x 26 mm) are dark in colour and
   have a thin, shell-like covering. They are being described in a separate
   paper."

  -- from Currie, P. J. and Chen P.-J. 2001. Anatomy of *Sinosauropteryx prima*
     from Liaoning, northeastern China. _Canadian Journal of Earth Sciences_
     38:1705-1727.

  This refutes my from-memory recall that the eggs were just in front of the
puboiliac contact, and it would imply something about shell being apparent in
the masses, but I would argue that their placement still puts doubt into their
identification of _in vivo_ eggs ready to lay.

  Cheers,

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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


                
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