Truly, the fossil record is quantized. Few creatures actually left a fossil for us to examine.
And indeed, the "tree of life" is a theoretical continuum which stands or falls based on those quantizations.
If scientists were to discover the fossil of a modern man in the same place as a fossil of a T-Rex, the tree would fall.
Why does the fossil record always show a different page out of the same story?
Why are there only extinct temperate fossils buried under the Antarctic ice, but no modern species?
Could it be that the fossil record, as incomplete as we all acknowledge it is, shows a story about what life forms inhabited the Earth at what times and in what sequence?
It seems the easiest explanation to me for why we only find rather small and mostly marsupial mammals in strata laid down during the age of the dinosaurs.