Re: DINOSAUR digest 3468 (Oviraptors=Parrots?)

["Jaime A. Headden" <qilongia@yahoo.com>]

Jean-Michel Benoit (s.aegyptiacus@wanadoo.fr) wrote:

<I don't know if it's been mentionned before but egg-crushing is not the only
way to open an egg. I can easily see an animal the size of "Oviraptor" could
pierce the egg just with its beak and hence having it open, without crushing it
in its jaws.>

  There are indeed two things to consider here. Jorge brings up both, and quite
insightfully:

  1) There is more than one way to open an eggshell. There are a variety of
animals that simpyl attempt to crack through the shell with an object (baboons,
humans, some birds like the marabou, etc.), or by dropping or using gravity to
open the shell (some birds like vultures), or by swallowing the shell and
purging its contents by slicing the shell itself (very few snakes), or by
crushing the entire object then picking the nutritious substances from the
shell, which is admittedly the most common since it, unless you're a tool-user,
requires fewer adaptations than the others (though African egg-eating snakes
are fairly adapted with hypapophyses of the vertebrae being transformed into
puncturing and slicing "blades"). This last model is used not for eggshell per
se, but much harder foods, though some skinks (such as the blue-tongued
Australian variety) and teiid (such as the Tegu) lizards do eat eggs by
crushing them intraorally. Those animals that do crush hard-shelled foods in
their mouth without puncturing devices include a host of fish and sharks,
frogs, etc. The easiest way to get here is to be already adapting to eating
insects or shellfish (such as walruses crushing clams), or skates and rays and
horn sharks, all of which use "pavement" arranged teeth to pulvertize prey
using extensively expanded jaw abductor muscles.

  2) Measuring the stuctural integrity of per-thickness eggshell and the amount
of muscle required to violate that integrity, and thus measure the mass of a
muscle designed per given output versus the shell it would regularly crack.
Work by such people as Wilga and Motta have been doing this muscular output
versus crushing for various elasmobranchs, and it's been done for tegus and
skinks, which have even been described for specific modifications of the
muscles. Muscular output was done on various birds, crocs, and mammals, and
some fossil animals have had their jaws analysed for resistance to forces, but
none of this data has been blended to morphological hypotheses of egg crushing
to date save for some work done on animals crunching bones.

  Cheers,

Jaime A. Headden

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

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