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Re: Egg-eating in mammals

On Mon, 22 May 2000, Jaime A. Headden wrote:

> Betty Cunningham wrote:
> <This instect eater [*Jeholodens*] was not eating eggs
> or ganging up to eat eggs, at least. What mammals from
> Mongolia or China are you referring to? Dr Luo
> suggests all early mammals that we've found are
> insectivourous.>

In answer to Betty: I don't know the animal Nessov is referring to.  As
soon as I find out, I will post it.  Secondly, mammals' teeth and diets
were diversifying before the end of the Cretaceous.

And Jamie said:
>   In fact, egg-eating requires a few features: a
> crushing surface, and a sagittal or parasagittal
> piercing apparatus.

I agree these features are required if the animal is crushing or otherwise
entering the egg with its teeth.  But it is important to note that most
egg predation done on ratites seems to be from simply knocking the eggs
together and lapping up the contents--in other words, no specific
adaptation required.

> ...no mammal has these anatomical adaptations, nor
> birds, and that may be why we see a lack of specialist
> egg-eaters in these groups. (See Gans, 1954; Grzimek
> et al. (eds.), 1956)

This, in itself, may have been a threat to egg layers.  Omnivores can
subsist on other things, then cash in on seasonal eggs.  Most
(all?) mammalian egg-eaters are omnivorous.  And yet, except in areas
where predator-density is relatively low (i.e., tundra, off shore
islands), most (all?) oviparous species depend on concealment for
protecting their nest.  This suggests that generalists are a sufficient
enough threat to keep extant oviparous species from laying in the open.