In a Reddit thread titled "Who Are the Elder Civilization?," u/Jhin-Roh starts the conversation by writing, "From the Fossil it looks like some bird shaped life form. And did they find them on Earth or some other Planet?"

The first season of Altered Carbon vaguely discusses the Elders and treats them as mysterious beings. Season 2 shows the last remaining Elder, which looks like a makeshift pterodactyl, but this creature is still shrouded in mystery as the audience never really finds out how the species created its otherworldly technology. In the show, the Elders made this unexplainable technology that led to Quellcrist Falconer (Rene Elise Goldsberry) inventing stacks.

The books, as another user responded, reveal more information about these beings: "In the books, they are a long dead avian species originating from, or at least having inhabited, Mars," the user writes. "They are very different from humanity a lot less social, for example. The back story is that Humanity ends up finding fossils and left over structures on Mars during the 21th century (not noticed before landing there because very ancient / underground); among those structures are stellar maps showing other planets Martians have settled."

As the user points out, Elders are dead in the books (a ploy the author admittedly used to get out of having to fully explain them), and the show drops the Martian description entirely. The user also mentioned that the books had humanity invent stack technology by itself.For better or worse, this powerful species, whether audience members refer to them as "Martians" or "Elders," have a vague description and history attached to them, and it would have been ideal for the TV series to explain them in greater detail in a subsequent third season that's unlikely at this point.

Nevertheless, the "bird-shaped life form" inhabited Mars and other planets in the books.

Read more:
What to know about the Elders from Altered Carbon - Looper