Heritage Auctions in Dallas has made the 75 percent complete fossil skeleton of a "Tyrannosaurus Bataar," a slightly smaller cousin of Tyrannosaurus Rex, the star attraction in an auction set to take place in New York, USA Today reported.
Promotional material lists its origin as Central Asia and the Gobi Desert.
Bolortsetseg Minjin of the Mongolian Academy of Sciences has asked Heritage Auctions in a letter to put off the auction until the origins of the fossil can be settled.
Heritage officials denied any problems with the fossil.
"These specimens entered the United States legally and were prepared in the United States legally," Heritage Auctions President Greg Rohan told USA Today in a telephone interview.
Although he declined to identify the owners of the skeleton, he said they have clear legal ownership.
"We know these consignees as reputable people, not somebody who dropped out of the blue," Rohan said.
However, paleontologist Mark Norell of the American Museum of Natural History in New York also wrote the auction house to question the origin of the skeleton.
"As someone who is intimately familiar with these faunas, these specimens were undoubtedly looted from Mongolia," his letter said.
"There is no legal mechanism (nor has there been for over 50 years) to remove vertebrate fossil material from Mongolia.
"As a professional paleontologist, I am appalled that these illegally collected specimens (with no associated documents regarding provenance) are being sold at auction," Norell said in the letter.