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Fwd: issues w sauropod eggs



In Ruxton's et al paper: "Incubation time as an important influence on
egg production and distribution into clutches for sauropod dinosaurs",
the authors argue that egg clutch mass seems very small given the size
of the parent. They therefore propose that sauropods followed a
strategy employed by small animals called "scatter hoarding"...that
is, they do in fact lay many eggs but they bury them in several places
and leave them unguarded. WhiIe I agree with their basic assumption
(that many nesting parameters...specifically in this article,
incubation time...are constrained by the need to avoid predation), I
doubt their hoarding hypothesis for the following reasons:

1. The authors claim that in comparison with other archosaurs (birds
and crocs), sauropods should have a greater clutch mass. But an
important determinant of clutch mass in birds is the amount of
predation. Birds that experience low-levels of predation tend to turn
their investment towards quality versus quantity. For sauropods, then,
a tenable alternate hypothesis is that their nest defense was
effective enough that they did not need large numbers of offspring.

2. The authors argue that scatter hoarding brings advantages even for
sauropods. Firstly, by spreading the risk between several caches, it
is assumed that discovery of one will not lead to discovery of
another. This sounds reasonable until one thinks about the problems
associated with a 60 ton animal trying to conceal its eggs. Cache
provisioning is usually done by smaller animals, i.e., animals that
can be stealthy. Any attempts at stealth by a sauropod would make good
subject matter for a Gary Larsen cartoon, but hard to take seriously
in the real world.

3.The inapplicability of the hoarder analogy becomes even more obvious
when the authors claim "the visual or olfactory cues that pilferers
might use to detect food are likely to be less strong from a small
cache than a larger one...". This must be true, but when one considers
that a "small" cache of an 80 ton Argentine titanosaur would have
approximately 20 eggs, each over a kilogram, it is difficult to
imagine the animal somehow limiting the cues...visual scrapings,
fluids, observability of the egg laying process itself, ripples in
coffee cups.

4. They then suggest that a small cache would not be worth the effort
of pilferers. Depending on the pilferer, I would suggest that an egg
mass of just 32 kilograms would be something of a bonanza!

The paper is a valuable contribution to this enigmatic topic. And
there are good discussions of many issues surrounding the reproductive
strategies of these animals. But I question their conclusion. I argue
that scatter hoarding is a strategy for animals capable of stealth,
and that this was unlikely for sauropods.