Did those dinosaurs really live near mud flats, or were they driven there by severe drought followed by torrential rains? Or was it part of a migration route driven by repeating cycles of drought and rain? (the fact that they are under many, many layers of sedimentary rock suggests the latter)
Similarly, were hominids living in that cave a plan A, plan B, or plan C? Plan B could be a "Helm's Deep" situation, where you go there when something goes wrong. While Plan C could be an 'any port in a storm' situation where unexpected weather caught you in an area you did not mean to stay.
Plan A might have been a biologically active region where life devours anything that stops moving for too long, the same way we have trouble finding evidence of these huge cultures in Central and South America.