Why might an alien species have evolved long, narrow appendages/protuberances that resemble rabbit ears but aren't ears, horns, or antlers?
They attach at the top and/or back and/or sides of the head like rabbit ears. They should extend to a length of 0.5-1 metre and may be rigid or semi-flexible, but not prehensile.
The species is intelligent and tool-using, standing roughly 2.5-3 metres tall. They are a transitional centauroid – two true legs, two true arms, two limbs that can serve either purpose as needed. The species is native to a terrestrial planet not dissimilar to Earth in any significant fashion.
Temperature regulation for the body or the brain seems obvious, but long and narrow wouldn't be as efficient as wide (elephant-like), would it?