The National Times - T-Rex skeleton on show in Zurich before auction

The Aathal Dinosaur Museum's curator was on Tuesday helping complete perhaps the world's biggest construction kit -- reassembling a 67-million-year-old T-Rex dubbed Trinity.

Trinity was sent to Zurich from Arizona in the United States in nine giant crates.

The 3.9-metre (12.8-foot) skeleton has been mounted on a red carpet and under crystal chandeliers in a Zurich concert hall, where it will be on public display before going under the hammer on April 18.

The Koller auction house has estimated it will fetch between six to eight million Swiss francs ($6.5-8.7 million).

But Christian Link, in charge of natural history memorabilia at Koller, said he believed that was a "pretty low" estimate.

Trinity is made up of bone material from three T-Rex specimens, excavated between 2008 and 2013 from the Hell Creek and Lance Creek formations in Montana and Wyoming in the United States.

The two sites are known for the discoveries of two other significant T-Rex skeletons that have gone to auction: Sue went under the hammer in 1997 for $8.4 million, and Stan, which took the world-record hammer price of $31.8 million at Christie's, in 2020.

Last year, Christie's withdrew another T-Rex skeleton days before it went on sale in Hong Kong, after doubts were reportedly raised about parts of the skeleton.

- 'Very, very old' -

Reassembling Trinity was no easy feat, Schicker-Siber told AFP as she secured another toe bone.

"The bones are very, very old. They are 67 million years old. So they are brittle, they have cracks," she said.

"They are stabilised, but you never know if there is a crack that you haven't seen so far... You have to have the glue ready."

Aart Walen, an exhibit preparator from the Netherlands with 30 years' experience assembling dinosaur skeletons, agreed.

"We didn't break anything yet," he said proudly, as he and his colleagues worked on two large ischium bones, which sat near the dinosaur's pelvic area where the eggs came out.

With a parakeet named Ethel perched on his shoulder, Walen filled in cracks in the bones, using what looked like dental tools and modelling compound.

It was important for the fixes to remain visible, he said, showing the dark lines where the fissures had been.

"You have to see where it has been repaired. There are some stories about fakes out there. We don't want that," he said, referring to the aborted Christie's auction.

Knocking on different parts of the bone, he also demonstrated the different sounds made on original bone and the plastic additions used to fill out the skeleton.

- Room for a T-Rex -

Just over half of the bone material in the skeleton comes from the three Tyrannosaurus specimens -- above the 50 percent level needed for experts to consider such a skeleton high quality.

Link said Koller was intent on being open and transparent about the origins of the bones that make up Trinity.

"Hence the name Trinity. We are not hiding in any way that this specimen comes from three different dig sites," he said.

The skeleton is being sold by a "private individual" who wants to remain anonymous.

Auction sales of dinosaur skeletons and other fossils have raked in tens of millions of dollars in recent years, but experts have warned the trade could be harmful to science by putting the specimens in private hands and out of the reach of researchers.

Link stressed though that 95 percent of known T-Rexes are currently in museums, and said any private collector who might snap up the skeleton was also likely to lend it out museums.

Personally, he said he would like to see a Swiss museum buy Trinity, adding "it would be nice to have it here permanently."

Schicker-Siber said the dinosaur museum she runs with her father outside Zurich unfortunately could not afford to acquire Trinity.

"But if somebody buys it and doesn't know where to put it, we have a museum (with room) for a T-Rex," she said.

L.A.Adams--TNT