Are there any known instances of evolutionarily distant species, whose ancestors could not interbreed, that happened to mutate enough over time (through convergent evolution or otherwise) to be fertile with one another over enough time?
For example (just randomly making this up):
Hyracortherium <-- nope --> Thecodonts
Mesohippus <-- nope --> Dinosaurs
Merychippus <-- nope --> Archaeopterx
Pilohippus <-- nope --> Falconiformes
Horse <-- yes, hippogriffs! --> Eagles
Barring some act of God/mad scientist, no. You and a house sparrow might have started with the same ancestors, but over time, yours and his have changed in really different ways. Your bodies have changed, yours growing bigger and heavier, his growing smaller and lighter. The things your genes do, and even the way they’re arranges on your body have changed, so that if you were to line your genes up next to his, they wouldn’t be able to correspond. And thus is true even of two different species that physically look similar.
Yup, I understand that, just wondered if by some inconceivable coincidence – a one in a trillion chance – an unlikely couple might’ve defied the improbable.
Even if two individuals, previously thought unable, managed to interbreed, how could we be sure that their prehistoric ancestors never did?
I guess it’s possible for something like this to happen:
Two subspecies diverge to the point that they strictly won’t interbreed (for some mechanical reason of morphology, mating behaviours, etc)
They remain biologically inter-fertile at an egg-and-sperm level upwards, but they just never mate
Some mutation happens to one or both that happens to reduce or remove the impediment to their mating - and they are then able to interbreed again
Yeah, I’m thinking something like size difference. If all dogs other than chihuahuas and St. Bernards were killed off, those two would become different species, but it’s possible that among their descendants, you’d have some giant chihuahuas and miniature Bernards that could interbreed.
How would we know whether two extinct populations could interbreed or not?
No, there are no known instances, because we don’t know which extinct species could interbreed.
Good point!
“More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct.” - Google
I’d have to say the “unknown” factor here is pretty significant. LOL
Good point!
DNA remnants? Geologically distinct intermediary fossils? Unlikely?
We know that modern humans could interbreed with extinct Neanderthals and other archaic humans due to DNA evidence. It would theoretically be possible to identify hybrids between two extinct species, but it would be difficult to prove that the parental species were unable to interbreed at some time before that and acquired the ability later.
The examples in the OP are so distant that interbreeding would clearly be impossible. The anatomy is so different that it would be impossible for an intermediate creature to exist even if an egg could be fertilized.
Generally gametic differences that prevent hybridization evolve after behavioral differences that do so. So two species can remain capable of producing offspring for a long time after they have speciated. Hybrids have been produced between species as distantly related as camels and llamas, although in this case by artificial insemination.
In principle, this would not be impossible for relatively closely related species. However, I am not aware of any cases, and proving it would be very difficult.