W hen you’re house-hunting, it is the easiest thing in the world to overlook whether your dream home is sitting on top of a stack of dinosaur bones. But that detail didn’t escape the attention of a seasoned American fossil hunter. Seemingly, there are more dinosaurs in his Colorado backyard than in Jurassic Park. He owns just under 100 acres and, in the past dozen years, has pulled 10 dinosaur fossils out of them – and believes that there are many more waiting to be found. But he would do well to beat the spectacular discovery that he has excavated in the past two years. It is a stegosaurus the size of a monster truck, and remarkably well-preserved for a creature that has been in the earth for 150 million years.

The owner has nicknamed it “Apex”, because it belongs to one of the dominant varieties of the stegosaurus family – four-legged plant-eaters with a jagged tail and great kite-shaped armoured plates on its back.

Apex is estimated to fetch between $4 million and $6 million when it comes to auction on 17 July. Cassandra Hatton, Sotheby’s senior vice president, and global head of science and popular culture, says it is the first time a specimen of this kind has been offered by a major international auction house. “This is an incredibly important discovery, and I don’t know of another stegosaurus that matches the size and quality of this one.” Hatton explains that Apex is approximately 11.5ft tall, 27ft long and 6ft wide – almost twice the size of Sophie, the stegosaurus in London’s Natural History Museum. “The quality of the fossil is excellent,” she adds. “Even impressions of the skin have been preserved.”

Apex was found on a walk by the owner and his friend, and it wasn’t the only stegosaurus they found. “We saw part of one and decided we’d come back for it later,” he recalls. “A few hundred yards on, we were walking up the side of a small mountain, and I said, ‘Wow, there’s a femur sticking out of the rock wall.’ It was right under my friend’s feet. We looked around and my friend found some vertebrae.”

An earth-moving machine was called in for the difficult task of shifting boulders weighing a tonne or more from directly above Apex. “I saw the spikes of the tail sticking out and a couple of the big plates on its back,” the owner says. “I could tell it was still curled up.” This was an ideal “death pose”, in fossil hunters’ jargon. Apex may have met its end in fast-running water, which pushed its long neck and tail behind its heavier torso, offering the best chance of a well-preserved skeleton. Typically, dinosaur fossil hunters encounter broken bones scattered like boxers’ teeth. Apex also benefited from bearing no signs of having fought other creatures. The only indication of wear and tear was that its lower vertebrae had fused with the pelvis, an effect of arthritis, suggesting the stegosaurus enjoyed a long life before an eternity in the ground.

The fossil hunter works with a team of up to a dozen people, including his father, who has had a lifelong interest in fossils and used to take him on field trips when he was a boy. After the team had recorded exhaustive data about where Apex was found, its remains were carefully taped up in protective “jackets” made of plaster and hessian, lifted onto a trailer and taken for careful preparation in a laboratory, stocked with equipment ranging from sand-blasting jets to pneumatic chisels. Fossilisation meant that the bones had been encased in rock; this was painstakingly removed to lay bare the animal’s skeleton. The individual bones will next be set on a custom metal mount, bespoke to the creature’s colossal proportions, in preparation for its preview exhibition at Sotheby’s New York galleries.

“Apex is 70% complete, which is incredible for a dinosaur, especially a stegosaurus,” says the owner. “Completeness” refers to the amount of the fossil that has been recovered. “To date, we are yet to discover a dinosaur that is 100% complete,” says Hatton. “After being in the ground for millions of years, tectonic shifts, weather and erosion result in fossils being broken into pieces and spread out; finding 50% of a dinosaur is considered to be a major scientific discovery, so 70% is an incredible amount.”

The cliff-face of clay, mud and sand where Apex was preserved is like a cross-section of the deposits that have settled in that part of the world through time. The owner’s ranch sits on the Morrison Formation, a stretch of sedimentary rock dating to the Jurassic period. Centred in Wyoming and Colorado, it covers 600,000 sq miles of western US and is a rich vein for discoveries. The owner compares fossil hunting in the region to “looking for gold coins when you know where the king’s counting house was”.

He calls his unusual pursuit “a romantic science of interest”. That may be true, but I have a hunch it also takes a lifetime of blood, sweat and soil to tell the difference between a dinosaur’s final resting place and a hole in the ground.

_{Cover photo credit: Matthew Sherman}

Past Auction

Natural History, including Apex the Stegosaurus

17 July 2024 | 10:00 AM EDT | New York