I really like the idea of them being, either physically, metaphorically, culturally, spiritually, or in any sense "bird-mer". The fact that they enslaved the daughters of kyne, who in nordic totems is portraid as a hawk, may lend another layer to this lore-onion. Or perhaps the whole idea is touched by sheo...

But still... bird-mer, yeah. I like that idea.

NO U

Ok, there're a lot of issues with treating Umaril as an accurate representation of the phylogeny of the Ayleid, BUT I really like the idea of them being bird people, so I'll just shut it.

From the pits of Peryite to the highest tip of the Greedy-Man's Throat I fought with the Quêteure of Apocypha... Until at last I raised up this Muthsera and severed his Sheorgorath upon it's chim aruhn... munax lumnaar took me, and I strayed into unahzaal vokun and alt'akaiit... The mnemoli varlais wheeled mathmeldi, and every day was as long as a kalpa of this Joor Zah Frul... But Satakal did not come. I felt Garlas Malatar in thy again. I've been brought back until Mathmalutu is built.

Pull my [amaranth]
tip my cup

all my [apertures] are open
Cut my thoughts

for [spore textracts]

How about this for a twist?

Maybe the giants of Skyrim were already there and the true people of Atmora are like Reiklings (For those that haven't played Bloodmoon - ice goblins found on northern side of the island Solstheim, north east of Skyrim). Then it would mean that it is the Nedes who were the giants, lol

Maybe the Aldmeri & Altmora are the same place as one is under ice and the other is under water (ice + water = H2O =same stuff). Then perhaps all the dirty elves, along with the dirty goblins are all descended from a race of halfpints hence the shared pointy ears?/!!. Only difference being is some mer evolved much taller.

[only joking around by the way - not a serious suggestion. I do think Aldmeri & Altmora sound suspiciously similar though, suggesting the mer & men have the same roots which would make sense as of them being on the same planet and both being humanoid races. The chance of two completely different species on the same planet independently evolving almost identical I'm sure wouldn't happen. And they are able to mate with one another and produce offsprings]

Atmora had Elves. It's name came from Altmora (High Forest) because it was the northenmost place visited by the Aldmer, and Orkey is believed to be an Aldmeri loangod, which would explain why he is the only instance of Arkay demonized other than what the Order of the Black Worm believe in.

Furthermore, Shor's old legends - from Atmora - are based around him overthrowing elven tyranny. There were elves in Atmora, and as SithisLorkhan mentions the Nords took Orkey from them, which hints that their cultures may have mixed.

maybe the Elven legends of Aldmeri are in fact a reference to Altmora hence them arriving before humans. The "under the sea" is a reference to it now being under ice. Perhaps they don't want to remember the facts that they were driven from Atmora by humans who they previously had ruled over.

Couldn't that just be because the Nords still have their origins in Tamriel, Their mythological birthplace is there and their voyage from Atmora to Tamriel is called a return after all.

True enough, but I'm not sure if Dawn Era cultures would have interacted as much.

If Talos was from Atmora, and we see him giving farewell to Atmoran King, it is probably not covered by ice to its coast. I think Atmora in 3d-4th Era is a big glacier but with thundra|/meadow coastline, just like Greenland (epithet of Atmora =) ). It is still inhabited though low-populated, half of their population are probably Giants.
I'm still waiting for it in DLC.