Question about evolution, genetic bottlenecks, and inbreeding

Think of a speciation event. A subpopulation is separated from the main population so that there is no gene flow. This daughter population carries a subset of the larger populations gene pool, will have unique mutations occuring within its population, and may experience different environmental pressures. Over many generations this daughter population becomes sufficiently different from the parent population that interbreeding cannot occur and they are regarded as a new species.
Now in this scenario, you will note it is the population that has become the new species over time, you can't point to an individual that is the new species. So how would you point to an individual that is the common ancestor? All the breeding individuals in the daughter population have contributed to this speciation event.