Answer:
It is D
this shows that there was likely greater diversity during the time that is represented by that rock layer
it could also be random chance that those fossils ended up being fossilized in that location as fossilization is a random and rare occurence so this is usually corraborated with multiple locations
also remember that a mass extinction event can fit within as large of a window as over 100k years because dating isn't bang on and a large cataclysmic even could take a long time for it to effect the whole planet enough to cause a mass extinction
Step-by-step explanation: