I happened to see a rhipidistian today here in Los Angeles, although it was hard to identify because it was wearing a face mask. 
Just learned a new word! TL : DR - an anadromous fish is one that lives in both fresh and salt water.
ETA: Colibri beat me to it!
I’m sure getting a lesson today in marine biology. Ostracods, rhipidistrian - what’s next?
Birds might not transport fish very far, but it doesn’t need to be very far. I can envision an eagle catching a fish in one river, flying over a ridge, and then dropping it into another nearby river that’s a different basin. It won’t get fish into Thawed Antarctica, or across a continent-spanning desert, but it could gradually populate basins.
I doubt it very much. Fish eagles and ospreys normally fish in larger rivers and lakes, not in small streams where they could just “cross a ridge” and be in a different watershed. Kingfishers might fish in small streams, but they would be extremely unlikely to carry live fish over a ridge.
When I was young there was a small cow pond in the field behind my grandfathers house. Every Sumer it dried up. Bone, earth cracking dry. But the spring rain would always refill it. And I would always catch fish in it until it dried up again. Usually only bluegill but still…
Don’t just drop stuff in here people. I’ve got way more important things to do during stay-at-home than look terms up.
“Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders.”
“The Rhipidistia, also known as dipnotetrapodomorphs (formally Dipnotetrapodomorpha) are a clade of lobe-finned fishes which include the tetrapods and lungfishes. Rhipidistia formerly referred to a subgroup of Sarcopterygii consisting of the Porolepiformes and Osteolepiformes, a definition that is now obsolete.”
Now I’m going to have to work that crap into my conversations.:rolleyes:
Well, it’s understandable that fish can repopulate it, given 4000 years.
This is sort of a specialty niche, but there are fish that “walk” between different bodies of water, i.e. the walking catfish* that plagues part of the American South (and similar fish in Australia).
*never pick up a hitchhiking fish holding a sign that says “Next Swamp Or Bust”.
Yellowstone Cutthroat Trout and possibly Lake Trout are thought to have crossed over the Atlantic-Pacific (i.e., the Great) Divide at the Parting of the Waters in Wyoming. (Wyoming has at least one other “either” hole in the Great Divide, Isa Lake, and one “neither” hole, the Great Divide Basin.) How many other oddities like this might’ve existed over geological time, across many different basins?
In the last few years I vaguely recall reading about a fish tagged in Montana but caught in Idaho; it was suspected that a bird caught it and dropped it, still living, into a different drainage. I might have the details or even the facts entirely wrong, though. I’ll keep looking and update if I find anything.
I dug up a photo of mine. It is better than I remember, and actually not too bad for their tiny size and a 2001-model digital camera.
It depends, since different kinds of freshwater fish have different levels of tolerance to saltwater.
Congratulations, you have excellent eyesight! And thank you and all the others for very interesting links and observations, you are helping me greatly. 
In North America I am talking about tens of thousands of years, that is, since the last glaciation: what has happened so far. But for Antarctica I am talking about all the time left in the future after the continent melts, if it ever does (and I guess it will, as it has done so in the remote past and humans are warming the Earth): whatever might happen in the future.
Thanks for the link, I did not expect that modern marine fishes are mostly freshwater fishes who went back. Nice!
It’s also worth considering that in longer periods of time, less normal events will occur - such as a water fowl being killed by a predator on arrival in the shallows of a new body of water, and that event emptying the bird’s crop into the water, for example - improving the survival chances of anything that happened to be in there.
There are plenty of places where a lake of significant size is very close to the edge of its basin. Yellowstone Lake is within an eagle’s flight of multiple divides (including the Great one), and even before the Chicago River was reversed, Lake Michigan was very close to the Mississippi basin.
A bird doesn’t have to drop a live fish either, it could be full of roe. I’ve never thought the bird theory was good for crossing oceans though. A bird could cross a continental divide, crossing an ocean with fish or eggs that will live doesn’t seem so likely.
Most fish have external fertilization, so without milt they won’t develop. And the eggs of freshwater fish usually need to be deposited in the right environment. Even if the bird opens the fish and dumps the eggs in the water, it’s unlikely they would develop.
Ah right. Doh :smack:
Sorry I’m not understanding your meaning.
He was punning on the fact that you misspelled summer as Sumer in your post.
It was an exceedingly obscure joke, and this being the Dope I am compelled to nitpick and point out it should have been 6000 years, not 4000 (no doubt the source of your confusion.)
I would instead have assumed you were using the Middle English spelling.