The aliens are very humanoid today. I hope that they are to your liking.
Cavemen:
There's no real explanation of why these cavemen are just chilling out in a cavern not a day's walk from an inhabited region of Africa, along with assorted mammoths and sabretooth tigers. They're just what Fantomah finds when she follows a river to its source to see why it has been contaminated and is killing those who drink from it. The answer: the cavemen killed a mammoth and just kind of lift it to rot in the water. Unusually, all of these prehistoric remnants are still there when Fantomah leaves, rather than being buried in a cave-in or exploded by a volcano as so frequently happens. (Jungle Comics 022, 1941)
Martians:
These very human-looking Martians at least have the good grace to have a weird history, as explained to Earthling Flint Baker: Hundreds of years earlier the Martian government had enacted a draconian Tough on Crime approach and thrown all of their criminals into an underground pit known as the Shaft of Death. However, due to a perpetual high wind rising from the depths, the Shaft of Death was actually a weird area of neutral buoyancy, allowing the criminals and their descendants to form an entire civilization that floats in midair.
Perhaps the most remarkable thing about this history is that the surface-dwelling Martians have no idea of what their ancestors did, and ignore Flint's warnings about an impending invasion from sub-Mars until it's too late and the drilling machines are on their front doorsteps. Worry not, for everything works out in the end. The sub-Martians are defeated and the subjected to brain treatments to remove their "criminal tendencies" proving that while the surface Martians might have forgotten their history, they are still very much willing to go to moral extremes in the eradication of Crime. (Planet Comics 009, 1940)
Martians:
These similarly-humanoid Martians from the same issue are much more straightforward evil conquerors out to hijack Uranus from its rightful human colonists. (Planet Comics 009, 1940)
Martians:
Finally, we have these still-humanoid-but-just-barely Martians encountered by junior space traveller Mitey Powers. These guys made me really excited when I saw them, as they represent a specific vision of what life on Mars might have looked like but which I frustratingly cannot find an image of due to the state of online image searching right now.
Essentially, this Martian represents a speculative evolution of humanity as it would look it it evolved on Mars, with huge lungs and ears thanks to the thin atmosphere, spindly limbs due to lower gravity, big flat feet to navigate the loose sandy surface, etc (one of the reasons I wanted to find another example of this is that there are justifications for the trunk and telescopic eyes but I can't remember them). Very exciting to see these guys walking around and having a society rather than just standing around as an example of their anatomy.
Speaking of their society, here are a couple of bonus tidbits: these Martians learn in their sleep (but must sleep sitting up due to their bulbous upper torsos) and play Blitzball from Final Fantasy X. (Superworld Comics 002, 1940)
