Inference of speciation mechanisms and sister species relationships are staples of evolutionary analyses, but are done almost exclusively on extant taxa. Distributions of living animals are generally taken as representative of the interplay between the biogeography of ancestral lineages and the (often vicariant) mechanisms that drove divergence. "Full sampling of all members of a clade" is correctly encouraged, but commonly excludes all but the denizens of the thinnest slice of geological time -- time zero, the Recent. The missing players of extinct taxa and the shifting stage of changing distributions through time are often brushed over or omitted as being too challenging. Detailed sampling through space and time of a species-rich molluscan clade allows us to test whether these simplifying assumptions are justified, or whether they bias our results. I present an example -- the Neotropical turrid genus Polystira-- that consists of narrow and widespread, rare and abundant, fossil and Recent species, to illustrate the contribution fossils make to understanding present day biogeography. This genus consists of numerous living and extinct cryptic, undescribed species whose discovery has been expedited by a combination of molecular genetic analyses with conchological studies of fossil and Recent specimens.