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Re: Brooding rex? (was Feathers for T. rex)



Ken Kinman wrote:

>      I've forgotten what shape therizinosaur eggs are, but the shell
> microstructure was not ornithoid (and not very elongate if I recall
> correctly).

Spherical eggs have been identified as therizinosaur eggs, because well
preserved embryos have been found inside them.  See Terry Manning's eggs in
_National Geographic_, May 1996.  Curiously, _Macroelongatoolithus_ eggs are
thought to also be therizinosaur, although the associated embryo (nicknamed
"Baby Louie") is not as well preserved, leaving open the possibility that these
belong to a different large asian theropod.  The article, "The Great Dinosaur
Egg Hunt," also shows a huge nest (about 8 foot diameter) of 26 such eggs
arranged radially (bicycle spoke fashion) about an empty center.  There is also
information on dinosaur eggs at the _National Geographic_ web site.

Among dinosaurs, I believe that we only have published skeletal evidence for
oviraptorids and troodontids preserved in a brooding posture.  These are
considerably smaller than _Tyrannosaurus_.  Troodontid clutches also typically
have a linear space through the middle where the parent breasted upon its eggs.

As far as shape goes, an elongate egg would provide the greatest egg volume
possible given the limitations of a small pubic passage.  Check out tyrannosaur
hips -- large eggs would not have fit between the ischia.  A larger hatchling
might be better able to survive to adulthood, especially among large parents (if
parental care continues after hatching).  Then again, with such large clutch
sizes, many theropod hatchlings must have died before they could reach breeding
age.

Bear in mind that brooding is not the only incubation strategy possible, or
large sauropods could not have possibly incubated their eggs!  In his highly
recommended book, _Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur
Reproduction_, Kenneth Carpenter notes that there are a variety of nesting
strategies used by reptiles (including birds) today.  In his Table 10.1 on page
158, he points out that brush turkeys, alligators, and crocodiles heat their
eggs with vegetation and earth mounds, and sea turtles and Komodo lizards bury
the eggs, which are warmed by the heat of the sun.  Some mallee fowl also use
volcanic ash to warm their eggs, and one can see this in David Attenborough's
"The Life of Birds."

Read Carpenter's book -- you are bound to learn something from it you don't
already know.

-------------Ralph W. Miller III
                    ralph.miller@alumni.usc.edu