In a Roosterteeth livestream on August 21, 2014, show staff confirmed that although mammalian faunus are most common, other types do exist. We haven’t seen them in the show yet.
Or have we? I think we’ve seen at least one reptilian faunus.
One of Neo’s most prominant traits is her changing eyes, seen in the first gif. I think that’s the first time we see them change in the show, actually. In Volume 3, we learned that she can change her physical appearance at will, like Mystique. Look how the Atlas disguise seems to flake off like scales. This also likely means that the other disguises she’s worn in the show, like the paramedic outfit, are part of her tranformative abilities. Cinder is also able to quickchange, as seen in “Dance Dance Infiltration”, but Neo’s is a passive ability and Cinder’s is an active ability. Okay, that was a tangent.
Two more pieces of supporting evidence, though even I admit they’re not the strongest. First, Neo is smol: 4′9″ in heels. Second, in “Painting the Town…” the female deer faunus wonders what a human was doing on stage while both Roman and Neo are on stage. It’s been hinted that some faunus can sense past a disguise of another faunus (in “The Stray”Sun knew Blake was a faunus), and the deer faunus only pointed out Roman.
Conclusion: Neo is a chameleon faunus.