I think the questions were more about the duration for
which taxa existed.
Oops! Yes, it was, sorry.
Well then.
- The fossil record is a pointillist affair. Most dinosaur "genera" are
known from a single specimen or from a few that have the same geological
age; we have no way of telling beginning and end.
- Genera don't exist. For the purposes of nomenclature, we have to pretend
they exist (as long as the PhyloCode isn't implemented yet), but they still
don't exist.
- Very few species concepts are applicable to terrestrial vertebrate
paleontology, which makes it very doubtful that the recognized species
correspond to anything that a neontologist with a time machine would
recognize as a species... under any of the 25 or more species concepts that
have been proposed so far. Remember, depending on the species concept there
are between 101 and 249 endemic bird species in Mexico.