Perhaps the hard bodied types lived at a different level or their body type predisposed them to being buried higher or they tried to get away and failed a little later than the ones that were maybe already under the sand or the ground? What if the time presupposition has nothing to do with it but uniformatarian principles are being assumed to be fact.
This is plain nonsense and/or fantasy. Many of the lifeforms were not mobile. They were anchored in position at the sediment/water interface. They are found were they are because thats where and when they lived.
Care to go to the
Uniformitarianism topic, and discuss what uniformitarianism actually is and isn't about? Read the earliest messages of that topic. That is where the good stuff is.
Moose