Hey Dude ...
Is there any example of such a case in the real world?
The phenomenon you are describing is refereed to as
adaptive radiation. And there are quite a few examples. Islands seem to be common places to find such ancestral species and daughter species existing at one time.
There are more than 800 species of drosophilid flies on the Hawaiian Islands.
The Hawaiian silverswords are another example: about 30 species in three genera -
Argyroxiphium, Dubautia, and Wilkesia
Darwin's finches are one of the most famous examples. Note that some say that this is just an example of beak sizes varying, not really speciation. Don't be fooled. There are some species that eat insects, some eat seeds of various sizes, some eat nectar - genera
Geospiza, CAmarhynchus, Cactospiza, Platyspiza and Certhidea. There may be a couple more too.
African cichlids are another good example of this also.
source:
Evolution, Douglas Futuyma, 2nd edition
Remember though, that the modern version of the ancestral species has probably changed somewhat since the two populations diverged, even with the lack of selection pressure, simply due to genetic drift.
Hope this helps
HBD
Edited by herebedragons, : No reason given.
Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for. But until the end of the present exile has come and terminated this our imperfection by which "we know in part," I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
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