This week, the American Museum of Natural History in New York will unveil its newest exhibit to the press: the skeleton of a huge plant-eating sauropod that many paleontologists think is the largest dinosaur ever discovered. The animal is new enough that it doesn’t yet have a proper scientific name — it’s being called Titanosaur for now. It is 122 feet long and 19 feet high at the midpoint of its back, a specimen so big that its head will peek out of the great hall of the Wallach Orientation Center and into the elevator bank on the fourth floor. Its dorsal vertebrae will brush the lofty ceiling.

But in the museum’s files is buried a description of a vertebra for a dinosaur that would have been 55 percent longer than the Titanosaur — and bigger than any animal ever known. The only problem: The vertebra described has been missing for more than 100 years, and many people think that it may never have existed at all, or at least not as it was described in the first place.

The missing dinosaur is known as Amphicoelias fragillimus, and the only recorded evidence of its existence — a piece of vertebra measuring almost 5 feet tall — is said to have been dug up just outside of Cañon City, a small town in central Colorado that for a few short years in the late 1800s was the dinosaur capital of the world. Along with dozens of bones from other dinosaurs, the partial vertebra is listed on the manifest of a freight train that went to Philadelphia, where it was first described and sketched in a paper by famed paleontologist Edward Drinker Cope. Around the time of Cope’s death in 1897, the Amphicoelias bone is said to have been sent with the rest of his massive collection to the American Museum of Natural History, where it was received and catalogued as FR 5777: “Amphicoelias fragillimus, Holotype.”

But when museum President Henry Osborn and his colleague Charles Mook finally got around to analyzing the collection more than two decades later, there was no Amphicoelias bone to catalog. In their exhaustive review of the sauropods of the Cope collection in January 1921, Osborn and Mook write, “The type of this species has not been found in the Cope Collection, and its characters cannot be clearly determined.”

It makes sense to be skeptical that an animal almost twice the length of a blue whale once roamed the American West.

A few months ago, I went searching for the truth about that missing bone. I was not the first — plenty of others have sought the largest dinosaur that has ever lived. What I found was a quest that has driven some people toward maniacal competition, some to conspiracy theories and others to disregard scientific consensus. It drove me to a little rocky outcropping on a hill in rural Colorado known as Cope’s Nipple.

My search started in Cañon City with Dan Grenard, a former Bureau of Land Management official turned amateur historian and paleontology enthusiast. Grenard is the kind of small-town resident who leads restoration projects, volunteers to share his knowledge with local middle-schoolers and knows pretty much everyone in the area.

When Grenard, a few others and I hiked into the hills behind Cañon City, we found the spot where Amphicoelias was likely uncovered. It was completely unremarkable. There was an ever-so-slight depression in the ground, and there were more light-colored rocks strewn about than in the surrounding areas. Melissa Smeins, who took over from Grenard as the Bureau of Land Management’s resident geologist, casually picked one up and handed it to me. “Dinosaur bone chip.”

Wait, what?

One hundred and thirty-eight years earlier, a seminarian-turned-teacher named Oramel Lucas had stood in the same spot — and also found bones. Lucas ran the one-room schoolhouse in the valley next to Fourmile Creek, which was a few miles north of Cañon City in an area now known as Garden Park. Lucas knew of other dinosaur digs going on in the area, but, as biologist Randy Moore writes in his book “Dinosaurs by the Decades,” Lucas may not have gone looking for them, instead simply stumbling across giant fossilized bones on a walk in the nearby hills. Whatever the provenance, he contacted one of his science professors at his alma mater, Oberlin College, who connected him to Cope. Lucas, it turned out, had wandered across a veritable Camarasaurus graveyard; over the next few years he’d pull six of these sauropods out of the 150-million-year-old green-and-red dirt layer in the hills known to geologists as the Morrison Formation.

Lucas’s biggest find, though, was yet to come. In 1878, Cope published a two-paragraph paper in The American Naturalist about it: “I have recently received from my indefatigable friend, Mr. O. W. Lucas, the almost entire neural arch of the vertebra of the largest saurian I have yet seen,” he wrote.

By that time Cañon City had changed. It had been a Western outpost where most townspeople worked as miners or shopkeepers and stagecoaches regularly rolled through the downtown strip bringing goods to the train station. In the 1870s, though, the cargo being transported shifted from ores to dinosaur bones as the town became ground zero for the growing rivalry between the two most famous men in paleontology: Cope and his rival, Othniel Charles Marsh.

This rivalry — now known as the Bone Wars — involved humiliation, bribery and eventually financial ruin for both sides. It also led to one of the most incredible periods of paleontological discovery in history, as the men’s rivalry led them to finance expeditions to the fossil bone beds of the West. Eventually, their teams identified more than 100 new dinosaur species, though many of those species have since been lumped together or otherwise revised. Amphicoelias fragillimus was one of the species discovered.

Marsh and Cope started out as friendly rivals, even naming new species after each other. Marsh was more academic and better funded — his millionaire uncle George Peabody built a museum at Yale for him — while Cope was more independent — he kept many of his favorite bones hanging in his Philadelphia house — and more prolific, cranking out more than a thousand academic papers. Cope eventually bought The American Naturalist to directly publish the notes on his finds. In Cope’s version of the story, their relationship soured when Marsh secretly bought bones from the workers at one of Cope’s quarries. In Marsh’s, the fallout happened after he publicly embarrassed Cope by pointing out that Cope’s Elasmosaurus reconstruction had its head literally coming out of its ass. Either way, the men went from sniping at each other to actively working against each other. At sites across the West, their workers were directed to sabotage one another, destroying rival camps, quarries and even bones.

Lucas’s findings didn’t go unnoticed by Marsh. As Lucas was shipping his first major haul out of the city, Marsh sent a Kansas professor named Benjamin Mudge to the area to persuade him to switch bosses. But Lucas was loyal to Cope, and thus the extremely large vertebra he found sticking out of the depression I was standing in was packed up and sent to Philadelphia.

One hundred and thirty-eight years later, I looked down at the rock Smeins had placed in my hand and saw that, yes — it was a dinosaur bone. There were little striations throughout the fossil, the telltale signs of carbon petrification. I looked around on the ground and there were little bits of dinosaur bone everywhere. Was I literally holding a piece of Amphicoelias in my hand? Who knows. As writer Brian Switek has explained, every paleo researcher is familiar with the feeling of finding a busted fossil. Where a beautiful bone once was, only unidentifiable fragments remain. Behold: the Chunkasaurus.

Grenard explained that the Amphicoelias probably existed a couple of million years after the other dinosaurs that were found there. That means that erosion exposed it first, and that many of the bones had likely shattered well before people could find them. Cope noted the thinning condition of the vertebra himself, calling the species fragillimus and noting that “much care was requisite to secure its preservation.”

Ken Carpenter, a short, stocky professor at Utah State University Eastern, spent 20 years trying to preserve something different: Cope’s discovery of Amphicoelias. In 2006, Carpenter tried to settle debate over the dinosaur by synthesizing his research in a paper titled “The Biggest of the Big.” It drew academic focus back to the dinosaur decades after it had been relegated to the sidelines.

For nearly two decades, Carpenter worked at the Denver Museum of Nature & Science, leading a team in charge of finding fossils. In 1992, while surveying the Garden Park area with his research assistant, he stumbled upon a huge find in a riverbank — a nearly intact Stegosaurus skeleton, one of the few that has been found.

The Stegosaurus made Carpenter a star in the paleontology world, but he was interested in an even more elusive quarry: Amphicoelias. He acknowledges that it’s most likely that the vertebra and any other Amphi bones have turned into Chunkasaurus, but he still spent years researching the animal and even more time combing the Colorado countryside looking for more Amphicoelias bones. When his traditional searches came up empty, he decided to bring in a ground-penetrating radar — generally used by excavation crews to make sure they don’t hit sewer lines — to see if he could find any bones still hiding under the surface. It was useless, since the fossils and rock matrix the bones are encased in turn out to have the same density. “It turns out it was nothing like ‘Jurassic Park,’” he says.

Carpenter, now 66 and silver-haired, was a little grumpy when I prodded him by phone about the big dinosaur; he says he has moved on from his monomaniacal pursuit of Amphicoelias. He now spends his field time looking for prehistoric mammals in northwestern Utah and calls the argument over the largest dinosaur a paleontological “dick-measuring contest” that he’s not interested in participating in. When I told him I may have been holding a piece of Amphi bone in my hand, he was unimpressed. “A bone fragment’s a bone fragment’s a bone fragment,” he says. But once I got him talking about his research into Amphi and the incredible lengths he went to to try to find more, he perked up and started getting excited, even wistful.

In his paper on Amphicoelias, Carpenter tried to synthesize everything known about the animal so far. He even reconstructed the missing bone out of plastic foam; after adding the missing parts, he had a vertebra that was more than 8.5 feet tall. Expanded along the dimensions of a Diplodocus skeleton, that results in an animal that’s 190 feet long. For comparison, blue whales can measure up to 100 feet long. “I’d like to model the entire skeleton,” he says. “But that’s still a pipe dream.”

ANIMAL LENGTH Amphicoelias fragillimus 190ft Titanosaur 122 Blue whale 98 Brontosaurus excelsus 72 Giant squid 59 Tyrannosarus rex 39 Triceratops horridus 26 African elephant 23 Stegosaurus stenops 21 Sources: Ken Carpenter, American Natural History Museum, The Princeton field guide to dinosaurs, national geographic

It makes sense to be skeptical that an animal almost twice the length of a blue whale — and more than 50 percent longer than any other known sauropod — once roamed the American West. For a long time, many in the paleontological world believed that it never existed at all, and that it was simply a fish tale Cope used to gain prestige in the ongoing battle with Marsh. But the fact that, as far as we know, Marsh never once took the opportunity to question the finding is instructive, as he would have loved to have more fodder to fight his rival. And although Osborn, director of the American Natural History Museum, bemoaned the missing bone in his survey of Cope’s collection, he was convinced it had existed.

Modern skeptics are less likely to believe that Amphi was fake than to believe that something else fishy was going on. Cary Woodruff is one such skeptic. He’s an adjunct instructor of earth sciences at Montana State University who specializes in studying sauropod vertebrae, and he’s not convinced that any dinosaur can get get much larger than 100 feet long. Early last year, in a paper titled “The Fragile Legacy of Amphicoelias fragillimus,” he and his co-author John Foster argue that not only is the Amphi bone likely just part of a Diplodocus specimen, it wasn’t even that big. Based on the other measurements in Cope’s notes — and the fact that Cope was notoriously careless in his rush to get out papers — they argue that the most likely explanation is that a typo changed the height of the vertebra from 1050 mm to 1500 mm, which would make it about a foot and a half shorter. “People have been working in the Morrison for 130-plus years, continuously,” Woodruff told me. “We have never found a single scrap of any other bone that’s even close to the size of what Amphicoelias is reported to be.”

Woodruff doesn’t think that Cope was trying to deceive anyone when he made his measurements, but that he realized soon after that his sizing was wrong. Woodruff’s theory? Cope wasn’t interested in being humiliated again as he was with Elasmosaurus, but he also didn’t want to perpetuate bad science. So he simply stopped talking about the great beast after his two-paragraph description in The American Naturalist. That would explain why Cope never mentioned Amphi in his later writings, even in his papers about evolution and larger body size that eventually became known as Cope’s Rule.

Carpenter disagrees, calling Woodruff’s theory of a cover-up a “pretty harsh accusation for a kid standing on the shoulder of a giant.”

And there’s another person who thinks the idea of a supersized sauropod may not be wrong out of hand: Nathan Myhrvold, the polymath CEO of Intellectual Ventures and former CTO of Microsoft. Myhrvold has recently turned his attention to dinosaur size. (In previous years, it’s been on cooking and nuclear power.) In a 2013 PLoS paper, he argues that most of our current size estimates of dinosaurs are wrong for two reasons: The first is that paleontologists aren’t great at using stats to approximate animal size from bone measurements. The second is that most of the individuals that scientists are using as prototypes for their species weren’t fully mature. “Unfortunately the specimens that have the most complete skeletons are not the very biggest ones,” Myhrvold told me over email. “I think that at some point we will find new specimens of enormous sauropod, and hopefully will have enough material to settle the matter. But even then, we may find scraps of something that might be even bigger.”

In the meantime, a small stream of large-dinosaur sleuths continue to make the trek to New York to see if there are any Amphicoelias clues at the American Museum of Natural History. Mark Norell, the current head of paleontology there, tells me that the big bone room was cleaned and recategorized eight years ago, so it’s impossible that the 5-foot-tall bone is in there. But he’s willing to leave a slight opening that it’s somewhere: “If you have a collection like ours — we’ve got nearly a million specimens — it’s like running a library. Things just disappear. Sometimes they show up years later.”

There’s a precedent for that. In 1998, a few amateur dinosaur hunters, including Jack McIntosh, a physics professor at Wesleyan who died last month, persuaded the museum to let them check out Cope’s files. Although Osborn and Mook had claimed there were no other records from the digs at Cañon City, McIntosh found several letters between Cope and Lucas, as well as Cope’s field notebook from a trip to Cañon City in 1879. In it was the first description of exactly where Amphi was found — Grenard and I used those notes to find the spot on Cope’s Nipple.

But those notes didn’t help us find more Amphicoelias specimens. So, after a long day out dinosaur hunting, I headed back to my hotel in Cañon City, the Quality Inn & Suites, and walked over to an alcove in the lobby next to the stairs. There, in the corner, was Carpenter’s reproduction of the Amphicoelias vertebra, mounted just like the other biggest dinosaur in the world, Titanosaur, minus a few hundred bones here and there. The model was too big to fit in his office, and the Denver Museum didn’t want it. So, thanks to a favor from a friend of Grenard’s who runs the hotel, it resides in the alcove, confusing tipsy guests on their way out of the bar for a smoke. It’s not the American Museum of Natural History, but for now, it will have to do.

CORRECTION (Jan. 11, 8:14 p.m.): An earlier version of this article misstated the tech company Nathan Myhrvold once worked for. He is the former CTO of Microsoft, not IBM.