Hypothetical ancestors

[Bryan Simon]

Cladistic analysis gives us clades in which the end-point taxa (be they
families, genera, species or any rank in between) represent extant taxa.
The region on a cladogram at which two clades diverge is given the
theoretical definition of a "hypothetical ancestor". In view of the
extremely large number of biological species in the world, surely it should
be possible that we actually come across these very ancestors in a few
cases, or am I being naive?  This would assist greatly in answering critics
among creationists who often pose the question "What happened to or how
come we never see the intermediates that must have been present at some
stage to be able to account for the evolutionary process?"  These ancestors
presumably can also be fossils?  Are there papers in the literature that
could provide me with useful information?