Detailed X-ray scans of two baby woolly mammoths unearthed in the Siberian Arctic reveal how they lived more than 40,000 years ago — and how they probably died.
The comprehensive analysis, published in the Journal of Paleontology, represents a forensic tour de force: Scientists reported their initial findings about the life and death of the Ice Age mammoths, nicknamed Lyuba and Khroma, almost three years ago. But since then they've fleshed out the story in a way that would make a "CSI" scriptwriter take notice.
Researchers say 2-month-old Khroma, named after the river in northeast Siberia near which it was discovered, had a brain slightly smaller than that of a newborn elephant — suggesting that the gestation period for mammoths was shorter. Meanwhile, 1-month-old Lyuba lived roughly 3,000 miles (5,000 kilometers) away, on the banks of the Yuribei River in northwest Siberia.
Although they came from different populations, both mammoths were born in the spring and fell victim to similar fates, the researchers said. Both appear to have been suffocated by breathing in mud, probably after falling into a lake (for Lyuba) or a river (for Khroma). Death did not come gently.
But this tale is about more than two poor baby mammoths. In a news release, University of Michigan paleontologist Daniel Fisher said the two sets of remains "can be thought of as Rosetta Stones that will help us interpret all the isolated baby mammoth bones that show up at other localities."
How to do mammoth CSI
Lyuba and Khroma are remarkable specimens because they were so well-preserved in the Siberian permafrost, even after more than 40,000 years. "In terms of tissue preservation, it's probably more so for Khroma than for Lyuba," said Adam Rountrey, a collections manager at the University of Michigan Museum of Paleontology who was one of Fisher's colleagues on the project.
Rountrey told NBC News that Lyuba's flesh had the look of beef jerky, while Khroma's muscle tissue was "bright red, and looked like fresh meat, basically."
Because of that remarkable preservation, Russian authorities put strict limits on studies of the remains. Researchers could take only a few samples of the tissue. That left CT scans, like the ones conducted routinely for medical purposes, as the best way to get an overall picture of the mammoths' condition.
Limited scans of Lyuba were done in Tokyo in 2009 and Wisconsin in 2010, but the entire 110-pound body was too big to fit into standard medical scanners. The whole-body scan was finally done in late 2010, using a super-sized scanner at Ford Motor Co.'s Nondestructive Evaluation Laboratory in Michigan — a device that was designed to look for flaws in vehicle transmissions. Meanwhile, Khroma underwent CT scans at two French hospitals.
Both mammoths' teeth were put through micro-CT scans at the University of Michigan School of Dentistry. Researchers counted the daily growth layers inside the teeth to determine that Lyuba died 30 to 35 days after birth, while Khroma lived only 52 to 57 days.
Unraveling the cause of death
The researchers saw ample evidence that the permafrost preserved the mummified mammoths' soft tissues, including muscles and fat, connective tissues and organs. Khroma appeared to have clotted blood inside intact blood vessels, and undigested milk in her stomach.
"It looked like you'd just popped the top on a container of yogurt," Fisher recalled. "It was that white. It was that smooth. Just fresh, creamy milk from mama mammoth."
But the biggest clues to the mystery surrounding the mammoths' deaths came from masses of sediment that were detected in the trunk, the throat and bronchial passages. That sediment, combined with the fact that both babies seemed otherwise healthy, led researchers to conclude that the mammoths breathed in mud and suffocated.
In Lyuba's case, the sediments included fine-grained vivianite, a mineral that commonly forms in oxygen-poor settings such as lake bottoms. Tiny nodules of vivianite were even detected on the surface of the skull and inside it. Those nodules probably formed after death as the result of bacteria-caused decomposition in a lake, the researchers said.
They suggest that Lyuba crashed through the ice while crossing the lake during Siberia's spring thaw — and sucked in the mud as she struggled to breathe.
Fisher and his colleagues propose a different scenario for Khroma's death: She appears to have fallen into a river, perhaps when the riverbank collapsed, and fractured her spinal column. As she lay in the mud, she breathed in the coarse sediment and choked.
Send in the clones?
The researchers said the remains of Lyuba and Khroma could help them unlock future mammoth mysteries.
"We can use them to understand how factors like location and age influenced the way mammoths grew into the huge adults that captivate us today," said another one of the study's co-authors, Zachary Calamari of the American Museum of Natural History.
Some researchers are trying to use genetic material from frozen mammoth remains to bring back the extinct creatures, or at least modify elephants to give them the traits of a woolly mammoth. Russian scientists are hoping to extract usable DNA from a well-preserved mammoth carcass that was uncovered last year. But Rountrey said he and his colleagues weren't pursuing the cloning angle.
"These two mammoths are spectacularly well-preserved, but as far as I know, there haven't been any intact nuclei or cells identified," Rountrey told NBC News. "It wasn't the focus of our work, so we weren't looking at that."
In addition to Fisher, Rountrey and Calamari, members of the research team included Ethan Shirley, Christopher Whalen, Alexei Tikhonov, Bernard Buigues, Frederic Lacombat, Semyon Grigoriev and Piotr Lazarev.