My current story has a planet called Herodotus. (Named from a Greek historian.) So if the planet had a sentient species living there, would we call them Herodotites? Herodians? Something else? Screw it, maybe I need to rename the planet
Ancient greek uses ...ian or ...ean (sometime ..ene ) for people who inhabit a country so herodians , herodeans or herodenes if you want to stay with the greek thing ... ite is the latin/roman ending , so herodites would be technically correct but the wrong school if the Greek cultural link is important
Strictly speaking, you can call them whatever you like - use your best judgement as a member of the Earthian race Personally, I always find it a bit weird when everyone's species is named after their planet, as if there's only one species living on each world. In the real world, there are plenty of examples of nonstandard demonyms and ethnonyms. Someone from Newcastle is a "Geordie", someone from Rio de Janeiro is a "Carioca", and "Persian" people still exist while Persia no longer does.
In this story, it would be odd to split the species up. The basic situation is this -- Humans named the planet Herodotus before they ever got there. When someone finally landed, they found the remains of a long-dead society. And although humans have colonized several planets by this point, it's the only sign of sentient life humans have ever found. Since they're essentially dealing with scattered archaeological digs at this time, they don't know enough about the species to start separating them into sub-classes. I think I'm going with Herodians. I can pronounce it easy enough.
Have you considered using that as a "catch-all" term for all the native species of that world? (I assume xenobiology would require the addition of a new high-level taxonomic rank anyway). I'm not really an expert here, but I wouldn't have thought it would be too difficult to differentiate wildly different species from fossil remains. Sub-species and similar-looking species, sure, but you're never going to mix up pufferfish, human and giraffe skeletons and not be sure which is which. I recently had a wander around the natural history museum in London, and a lot of the dinosaur exhibits give english translations of the latin names - I would imagine extinct alien species would probably be named similarly; according to rough descriptions, obvious characteristics, locations found and first discoverers. Scientists are people, rather than automatic processes. Their perceptions, personalities and even vanity colour what the species ends up being called.
If the sequel includes a scene on that planet, I may have to get into more detailed scientific names. The current WIP only has a character mentioning the planet and what's there because of unrelated things.