Josh Chait, director of the I.M. Chait Gallery, said an anonymous private collector hired the gallery to auction the 150 million-year-old skeleton next month, the New York Post reported Tuesday.
"He got it straight from the paleontologists who discovered it in Wyoming in 1993," Chait said of the collector.
He said the 6-foot-tall dinosaur featured long legs, a heavy tail, a horned beak and short hands with five fingers.
"The bones display a lovely soft, creamy coloring," the auction's catalogue says.
Chait said the skeleton is expected to sell for between $440,000 and $500,000.
"This is the largest and most complete skeleton we have ever sold," he said.