Plausibility of ancient extraterrestrials

[Anomalocaris]

The very same "gods" were described across multiple cultures all over the planet.

Yeah, if you close one eye and squint the other just right it's all the same, ain't it.

There are many different reasons why there can be resemblances between myths of different cultures that any mere resemblance could hardly be pinned down to any specific cause.     Some of the possible causes are:

1.  Culture contact and diffusion, either directly or through any number of intermediaries.    We have direct evidence that at least as early as the early Bronze Age there had been trade networks that exchanged people, raw material and products spanning almost the whole width of Euroasian continent, both in the southern areas with incipient urbanism, and north nomadic steppes.

2.  Shared origins in a common ancient founder myth.   We know some myths can be extremely enduring.  The leopard goddess culture seems to have had a central role in various Anatolian culture over a a period of 9000 years spanning from start of early Neolithic incipient agricultural cultures 12,000 years ago all the way to the fall of the Iron Age Hittite empire around 3000 years ago.    So resemblance between myths could point to the myths being very old and originated from an otherwise unremembered common founder myth.    

3.  Forms following function.    Myths that don’t tell a true story were concocted to meet a need.    If the needs were similar between two societies, then one would think the resulting myth designed to serve the need would also have heightened chance of exhibiting resemblances.