An iconic movie moment from the '90s is hitting the auction block ... it's the mechanical rhinoceros that gave birth to Ace Ventura in a Jim Carrey sequel.

Yes, the butt birth rhino from "Ace Ventura: When Nature Calls" is up for grabs over at Propstore's upcoming auction ... with the movie prop expected to fetch between $4,000 and $8,000.

It's the same rhino from the movie scenes where Ace is inside spying on some bad guys ... before escaping through the rhino's butt in a comedic exit.

The rhino measures in at more 10 feet long from tip to tail ... and it's got hydraulic hinges, a foam tail, padded interior chair, and a removable latex backside ... like the one Ace was birthed from.

Plus, the rhino has the same prop fan from the movie ... IYKYK.

The mechanical safari animal is made from fiberglass, and the legs are hard-coated Styrofoam ... so it seems easier to transport than a real rhino.

"Ace Ventura: When Nature Calls" was a box office hit, raking in over $212 million ... but it was also part of pop culture, with the rhino scene widely regarded as one of the funniest movie moments in the 1990s.

The auction starts March 27 ... all righty then.