Alternative humanoids to occupy late Eocene Antarctica

Question

So here's the idea, ~35 million years ago Antarctica was still quite habitable. This is far to early for hominids but what if a humanoid species arose in South America and migrated south into Antarctica? What kind of ancestor could work? They would have the look roughly human but don't have to look identical. But from a simple description be mistaken for a human, so no tails but a face like a bonobo could certainly work.

My first idea was take a common ancestor from the capucin monkeys and drag them through the aquatic ape hypothesis but there's no way to make that timeline work before climate change freezes over the continent. The goal is them having reach something akin to the bronze age at 35 million years ago, ideally the Antarctic coastline is still tropical.

So I'm looking for a probable ancestor for my humanoids and what vestigial traits that would force me to incorporate.

So our requirements are this:

• Humanoid in appearance Hands complex enough for tool manufactering

• Color vision but doesn't need to be identical to humans but something relatively close

• Human level intelligence in time to reach the late bronze age before Antarctica becomes to cold to occupy the inland area.

• Ability to live all over the continent, from the swampy coasts to the dry inland near the pole.

• Evolved in a place so it crossed into Antarctica from South America, this can technically be from Africa and came during along with the ancestors of the New World Monkeys e.g.

Answer 1

An early platyrrhine primate like Perupithecus

The oldest known platyrrhines date to 35-38 Ma. They are thought to have gotten to South America some time before that, potentially at the same time as the earliest South American rodents, which are about 42 Ma. That gives you about 7-8 Ma to play with, about the same amount of time as it took us to evolve from our last common ancestor with chimpanzees and drop down from the trees. So it's doable.

On top of that South America experienced opening grasslands earlier than other continents (though in this case it was more of palmetto scrub and C3 grasses than C4 grasses), so the selective pressure for a humanoid body shape is there. This started in the middle Eocene (~45 Ma) and continued into the Oligocene. There's actually an Oligocene (~26 Ma) platyrrhine, Branisella, that appears to have been specialized for running on the ground like a Patas monkey. So the environment supports it. Only downside is your humanoids are going to be a bit Sun Wukong-esque and have tails (there is really no reason to get rid of one if you're going straight to ground, apes lost theirs because of their manner of arboreal locomotion). If you don't mind missing the Antarctic glaciation having a lineage of sapient Branisella descendents mucking around isolated South America for millions of years might work better.

Full disclaimer, there’s no evidence that primates ever got as far south as Argentina until Miocene times, but the good thing about humanoid body shape is that once they achieve it they can spread everywhere in a geologic eyeblink (thousands of years), much like how humans spread out from Africa to every continent in less than 40,000 years.

Humanoid body shapes are tricky. You might be able to get sapience but you probably can't easily force a notopithecine notoungulate or a polydolopid metatherian to adopt a humanoid body shape as easily as you can another primate. Plus most of the endemic South American mammals are as dumb as a sack of bricks, not good candidates for sapience.

The one big problem is your species isn't going to be restricted to Antarctica. If they're present in Antarctica they can just walk to South America and Australia due to the three being connected by land until ~35 Ma, and that's not even getting into whether or not they can build boats. They might lose Antarctica but they will still have significant population centers on two continents, unless you make Antarctica their cradle of civilization or something.

Answer 2

The precursors to primates were also related to lemurs... simians and prosimians. There are intermediate species, of course, of which we only have the tarsier today. Lemurs have grasping hands, females can possess color vision in diurnal species (color vision is only advantageous for diurnal species). Primitive primates existed as early as 65 million years ago with many of these being closer to lemur than monkey. Subfossil lemurs such as sloth lemurs, and koala lemurs that were large and ape-like show in principle that lemur-like primates could occupy the same evolutionary niche as larger primates like apes (and by extension humans). For these to reach Antartica, during the warmer wetter period of history, these already rare mammals would have to have lived near the ocean and be swept all the way to Antartica, and have a surviving breeding population group in large enough amounts and in close proximity. This theory may require a vegetative raft. Twenty million years is a long time, even in evolutionary terms. The chimpanzee is likely only separated from humanity by about 2 million years. Now the question is of niche. Diurnal populations that need color vision would need to forage on fruit. Bipedalism is thought to have evolved due to walking across plains (or alternatively, shallow lakes... as in the aquatic ape theory). So to get it right, small patches of productive forest have to be separated by plains, which could seasonally flood. This could have been possible in Antartica. Pressures from the monkeys caused the lemurs extinction, but Antartica was not populated with monkeys, so the lemurs would have survived and flourished in greater variety. Diminishing forests force the lemur-apes to eat meat, which lead to greater brain mass. Hybrid vigor from closely related lemur apes also contributes to this effect. Eventually, human level intellect peaks with a lemur-sapian and small "accidents" lead to the discovery of agriculture (seeds mixed with kitchen waste, ashes, etc, lead to crops). Soft metals are discovered (because smashing rocks and burning stuff is the way to go if you are an intelligent ape-like creature) and lead to copper, meteorite iron tools, and other cool things. Civilization arises when a pot of grain porridge is left in the rain and ferments, making an alcoholic beverage. The resulting ceremonial liquid causes settlement to so lemur-sapiens can grow more grain, and religion because alcohol creates otherworldly experiences. All this in the span of somewhere between 20 and 30 million years due to an accidental rafting trip.