Probably, each being unaware of the other, they
pounced upon an ancestor of that
marsupial-which-must-not-be-named...
?
Anyway... expulsion by bloating of the carcass is the standard explanation
for the several fossil ichthyosaur "births", and what looks like a good
summary of the "rainstorms, not sandstorms" hypothesis can be found here
http://www.dinosauria.com/jdp/fossil/sandslide.html.
I wouldn't expect an earthquake in Mongolia in the Late Cretaceous.