NEW YORK (Bloomberg) — A pair of dinosaur turds, about 140 million years old, will go on the block tomorrow at Bonhams in New York. The rusty-brown mounds, known in scientific circles as "coprolite," are estimated to fetch more than $350.

Coprolite comes cheaper than other dinosaur fossils.

"Most people think of dino dung and think, `Why would I want to have that on my shelf?"' said Thomas Lindgren, the Bonhams specialist in charge of the natural history sale. On the plus side, Lindgren said, the dung "no longer smells."

The seller is a Utah private collector who found the five- and seven-inch, two-pound specimens in the Morrison Formation, a layer of sedimentary rock dating back 150 million years, spanning several Western states and known for dinosaur fossils. To the untrained eye, coprolite resembles an ordinary rock.

"The appeal is that it's from a dinosaur," Lindgren said. "This is one of those items that strikes a curious nerve. It's just a great conversation piece."

The Bonhams natural history sale also includes a 925-pound speckled meteorite discovered in Fukang, China, in 2000 and estimated to fetch as much as $2.75 million. The seller is Marvin Killgore, a plumber-turned-meteorite hunter and curator at University of Arizona's Southwest Meteorite Center.