There is, no doubt, a correlation between geography and evolution. Take the origins for the theory of natural selection (galapagos) and you've got your proof. Stingrays have been around longer than the fish we consider to be ancient fish (like bichirs, lungfish, knifefish, arowanas, bowfins, etc.), because the bony fish actually evolved after cartilaginous fish such as stingrays and sharks, thus there's been a lot of time put into their evolution, and I imagine that in the past, there have been significant periods of time (centuries to millenia) that have isolated groups of rays from one another (polar ice cap expansion, severe south american drought), and thus caused variations through a few dozen generations of inbreeding. Then when they were reunited from normal rains returning, the species were still able to hybridize, but had gained much different characteristics. It's all a very interesting topic, and I think it can all be traced back to major geographical and geological events in our history.
Question: The last Ice Age occurred approximately 600,000 years ago, and water levels were at extreme lows (and thus, many rivers were dried out). For any stingrays that survived the extreme cold and low water levels (the ones near the equator), could the transitions of this Ice Age have been a new beginning in Stingray evolution and diversification(and many species of freshwater fish)?
(Sorry for the novel... interesting topic)
