[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

EGG SIZES



        I am glad that my question about dinosaur egg sizes (below) has drawn
interesting discussions and received so many replies.

>         What size were the largest dinosaur eggs ever found and where were
they
> unearthed (I know that the eggs attributed to Hypselosaurus no longer hold
> the record of size)?   Is there any hint of which species laid them?    And
> how big would possibly be the eggs of giant sauropods such as Brachiosaurus
> and Antarctosaurus?    Is it possible that they were live-bearing (once they
> would, otherwise, have to lay eggs that would be above the size limit to
> which a reptilian egg can possibly get)?

Among those who replied was Dr. William Monteleone.   I would like to
discuss the main points of his reply, which are summarized below:

>The largest dinosaur eggs I have seen are Approximately 45cm high, and
>about 13cm in diameter (...) They seem to be laid in pairs, and are from
Mongolia (...) >Guesses on who laid' em run variously from Tarbosaurus
bataar, to Therizinosaurs.

>About a year and a half ago, Brian Cooley with TMP did a reconstruction
>which made the cover of National Geographic. (...). Based on his study, and
that of several
>others, he showed it as a large Therizinosaur. It's not clear whether
>this animal is a prosauropod or an ornithomimid (...).

>But what about sauropods? Well, we believe they had roughly spherical
>eggs, (of which there are many different types known.) Embryonic
>Camarasaur material led Brooks Britt and Bruce Naylor to estimate an egg
>size of about 24cm dia. While smaller than the largest know bird egg,
>(34cm high x 24cm dia from Aepyornis,) this is still a big egg.

>Eggs from Argentina attributable to titanosaurids are typically 11.5cm
>in dia, although I have seen some as large as 17cm. They look like
>cantaloupes! So did larger sauropods have larger eggs? Probably, but not
>necessarily. Kiwis have an enormous egg relative to their body size It
>looks as if eggs tend to get bigger as a species gets bigger, but they
>don't get smaller so easily. What happens is that dwarf species wind up
>with ridiculously large eggs.

>As for live birth, it has been suggested in the literature, but there is
>no direct evidence for it in dinosaurs. With so many new egg forms
>turning up these days, it looks like eggs were the favored method of
>delivery.

>William Monteleone



        It seems to me that the eggs of relatively small dinosaurs (e.g.
Oviraptorids, Troodontids, Hypsilophodontids, protoceratops, etc.) tend to
be relatively large considering the size of adults.   The
egg-size/adult-size ratios are apparently within the range of birds.

        Sauropods, on the other hand, seem to me to be on the other side of the
scale.   An egg measuring 24 cm in diameter is indeed a big egg for a bird,
but for a camarasaur it is ridiculously small (even considering that
Camarasaurus was a relative lightweight among sauropods; yet it outweighed
the elephant-bird by a wide margin).   The supposed titanosaurid eggs from
Argentina are even smaller (11.5-17 cm) and yet even the smallest
titanosaurs were surely elephant-sized, while the largest (e.g.
Antarctosaurus) were multi-ton behemoths.   It is not easy for me to
visualize such beasties laying such insignificantly small eggs, each of them
weighing an infinitesimal fraction of their adult weight (they would
probably have needed a lot of care not to crush their clutches with their
tails).   An embryo hatching from a 17 or 24-cm egg would be only the size
of a large lizard, and its growing to the size of an elephant (and usually
much bigger) would either demand a very long time or an extraordinarily fast
growth rate to maturity.    The first alternative seems unlikely, if viewed
from the scope of some recent theories that pressupose that sauropods may
have taken no longer than twenty years to reach adult size (otherwise they
would be highly prone to predation for a very long period, resulting in high
rates of mortality before breeding age, whoch is quite undesirable in
evolutionary terms).    Thus, sauropods may have been really fast growers
(what a lot of energy would be required to fuel such growth!).

        Some living reptiles such as sea-turtles lay very small eggs compared to
their adult sizes, but sauropods, if the evidences are correct, may
represent the lowest egg mass-to-body mass ratio known among land-breeding
vertebrates.   This fact may have led some to wonder whether some of the
largest sauropods were viviparous, and this conjecture has been reinforced
by some observations, such as wide pelvic apertures in some Apatosaurus
specimens.    Although Dr. Monteleone has suggested that egg-laying may have
been the rule among dinosaurs, it should be remembered that it is among
modern reptiles as well, and yet viviparity occurs across many taxa.

        Still on the Argentinian eggs, I recall having read in a book called
"Hunting Dinosaurs" (I don't remember the author) that some roughly
spherical eggs found in argentinian badlands had estimated volumes of four
to six gallons.   I suppose eggs this capacious ought to have been quite
bigger than the 17 cm cited by Dr. Monteleone (by the way, what would be the
diameter of a six-gallon egg?).

        Last of all, thanks for all those who replied my message (in spite of 
your
replies having raised so many more questions; but that's how science works
anyway!).