For all we know, this type of hybridization could be common. If it’s a bottom dweller, who was looking? Maybe hybridization plays a bigger role in evolution than we supposed. And then schoolbook Darwinism plays a smaller one.
It turns out that low genetic diversity is not necessarily a death sentence. It depends on what else is going on, perhaps. By the way, we still don’t know why the narwhal has a three-metre tusk (tooth).