Sitting inside a glass diorama at Chicago's Field Museum sit the stuffed bodies of two rather odd-looking lions. Although both males, they lack manes. Their faces seem too thin, their pelts look overly smooth for a large cat. One of them lies in repose, while the other stands ever-so-slightly at alert.

The rather sedate display doesn't quite convey the history of these two animals. They are the infamous Tsavo man-eaters, two lions accused of killing and eating as many as 135 men in Kenya in 1898. The stuff of legend, the deadly Tsavo lions were spoken about in whispers for decades and have since been dramatized in books, movies and even video games. They also remain an active subject of research, as scientists try to unlock clues as to why they killed and how many people they took down.

The story of the Tsavo lions begins in March 1898, when a team of Indian workers led by British Lt. Col. John Henry Patterson arrived in Kenya to build a bridge over the Tsavo River, as part of the Kenya-Uganda Railway project. The project, it seems, was doomed from the start. As Bruce Patterson (no relation) writes in his book "The Lions of Tsavo," "Few of the men at the railhead knew that the name itself was a warning. Tsavo means 'place of slaughter'" in the local language. That actually referred to killings by the Maasai people, who attacked weaker tribes and took no prisoners, but it was still a bad omen.

Men started to disappear

Lt. Col. Patterson and company had only just arrived when they noticed that one of their men, a porter, had gone missing. A search quickly uncovered his mutilated body. Patterson, fearing that a lion had killed his employee, set out the next day to find the beast. Instead he stumbled upon other corpses, all men who had disappeared from previous expeditions.

Almost immediately, a second of Patterson's men disappeared. By April, the count had grown to 17. And this was just the beginning. The killings continued for months as the lions circumvented every fence, barrier and trap erected to keep them out. Hundreds of workers fled the site, putting a stop to bridge construction. Those who remained lived in fear of the night.

The violence didn't end until December, when Patterson finally stalked and killed the two lions that he blamed for the killings. It wasn't an easy hunt. The first lion fell on Dec. 9, but it took Patterson nearly three more weeks to deal with the second. By then, Patterson claimed, the lions had killed a total of 135 people from his crew. (The Ugandan Railway Company downplayed the claim, putting the death toll at just 28.)

The threat over, work on the bridge began once again. It was completed in February. Patterson kept the lions' skins and skulls (like all male lions in the region, they lacked the normal manes characteristic of the kings of beasts) and in 1907, he wrote a bestselling book about the attacks, "The Man-Eaters of Tsavo." A quarter-century later the skins and bones were sold to the Field Museum, where they were stuffed, mounted and placed on display, where they remain.

Studying the lions

The man-eating lions of Tsavo in the Field Museum of Natural History. The man-eating lions of Tsavo in the Field Museum of Natural History. (Photo: Wikipedia)

But that wasn't the end of the story. Bruce Patterson, a Field Museum zoologist and curator, spent years studying the lions, as did others. Chemical tests of their hair keratin and bone collagen confirmed that they had eaten human flesh in the few months before they were shot. But the tests revealed something else: one of the lions had eaten 11 people. The other had eaten 24. That put the total at just 35 deaths, far lower than the 135 claimed by Lt. Col. Patterson.

"This has been a historical puzzle for years, and the discrepancy is now finally being addressed," Nathaniel J. Dominy, an associate professor of anthropology at the University of California Santa Cruz, said in 2009. "We can imagine that the railroad company might have had reasons to want to minimize the number of victims, and Patterson might have had reasons to inflate the number. So who do you trust? We're removing all those factors and getting down to data."

That doesn't mean the deaths weren't significant, or that what Lt. Col. Patterson called a "reign of terror" wasn't just that. The tests on the Tsavo lion bodies confirmed that one of the lions in particular preyed on humans, revealing that half of its diet during the nine months before its death consisted of human flesh. The rest came from eating local herbivores.

The researchers did, however, support the narrative that the two lions worked together as some sort of killing unit. They theorize that the two males came in together to scatter their prey, something most lions normally only do when hunting large animals such as zebras. One then concentrated on human prey while the other mostly fed on herbivores. This alone makes the Tsavo lions unique: "The idea that the two lions were going in as a team yet exhibiting these dietary preferences has never been seen before or since," Dominy said.

A look at dental wear and tear

Tsavo lion teeth The Tsavo lions had obvious injuries to their teeth that likely prevented them from crunching on bones. (Photo: DeSantis/Patterson)

More recently in 2017, zoologist Patterson and paleoecologist Larisa DeSantis looked deeper into the lions' diets by studying the clues found on the animals teeth, called dental microwear texture analysis (DMTA). They looked not only at the Tsavo lions, but also a lion from Mfuwe that killed and ate six people in 1991. Their new research was published in the journal Scientific Reports.

Because earlier witnesses said that they could hear the lions crunching on bones, the researchers said that if that were true, those dietary habits would certainly have left an impact on the lions' teeth. But they found no corroboration dental evidence to support those gory claims.

“We thought we were going to provide concrete evidence that these lions were scavenging and thoroughly consuming carcasses before they died,” DeSantis told Smithsonian magazine. Instead, "the man-eating lions have microscopic wear patterns similar to captive lions that are typically provided with softer food.”

In this case, the softer food was human flesh. The lions may have skipped the bones because of their own preferences, the researchers speculate, or because they had jaw injuries that would have made the fleshy parts much more attractive.

The researchers concluded, "DMTA data here suggests that man-eating lions didn’t completely consume carcasses of humans or ungulates. Instead, humans likely supplemented an already diverse diet."

A reminder of 'morbid fascination'

So why did the lions start killing people in the first place? The earlier study revealed that the lion that ate the most people had dental diseases, a poorly aligned jaw and damage to its skull. It may have turned to humans out of desperation. Meanwhile the time of the Tsavo killings followed a period of decline in other prey, mostly of elephants. That's when humans entered the picture and became an easy replacement dinner.

Although we now know more of the truth about the Tsavo lions, they still stand as powerful symbols of their day. "The signal feat of the Tsavo lions is that they stopped the British Empire, at the height of its imperial power, literally in its tracks at Tsavo," Bruce Patterson told the Chicago Tribune in 2009. "It was not until Col. Patterson dispatched them that work on the railway could resume." He also said the lions remain a reminder of the "morbid fascination in considering the business end of an animal that can kill and eat you in seconds."

Editor's note: This story has been updated since it was originally published in April 2014.