The skeletons of the two baby woolly mammoths, nicknamed Lyuba and Khroma, were found back in 2007 and 2009 respectively. Though scientists first reported their research on the remains nearly three years ago, they have since conducted a more in-depth analysis using cutting-edge X-ray technology. Their comprehensive findings, published in the Journal of Paleontology this week, shed considerable light on what we know about this Ice-Age mammal.
Mammoth fossils have been discovered in deposits dating to the Pleistocene Epoch (from 2.6 million years ago to 11,700 years ago) on every continent except for Australia and South America. In North America, evidence suggests small populations survived into the early Holocene Epoch, which began 11,700 years ago and continues to today. Primitive cave dwellers in Europe depicted in their art herds of mammoths, which were as large as modern elephants.
The Woolly mammoth, also known as the Northern, or Siberian mammoth (M. primigenius), is the best known of all mammoth species. Due to the region’s permanently frozen ground, a relatively large number of well preserved mammoth carcasses have been discovered in Siberia, allowing scientists to learn a great deal about the species’ structure and habits.
Khroma was named after the river in northern Siberia near which her remains were discovered, while Lyuba lived around 3,000 miles (5,000 kilometers) away, on the banks of the Yuribei River in northwest Siberia. Khroma was initially identified as male, but high-tech scans later enabled scientists to correct the mistake. Because the two baby mammoths’ remains were so startlingly well preserved in permafrost, Russian authorities put strict limits on their study. Researchers, allowed to take only small samples of the tissue, turned to computed tomography (CT) scans, similar to those often conducted for medical procedures, to get an overall picture of the animals’ structure.
The researchers working with Khroma and Lyuba faced a challenge, however: the size and shape of a baby mammoth meant it couldn’t be passed through a standard CT scanner. Limited scans of Lyuba’s 110-pound body were done in Tokyo in 2009 and Wisconsin in 2010, but it wasn’t until later in 2010 that an opportunity arose to conduct a full-body scan. While the remains were being transported from Chicago’s Field Museum to the Liberty Science Center in New Jersey, mammoth expert Daniel Fisher and his colleagues at the University of Michigan convinced their Russian handlers to stop in Detroit. There, at the Ford Motor Company’s Nondestructive Evaluation Laboratory, they used an extra-large scanner (designed to look into vehicle transmissions and engine blocks) to examine the baby mammoth skeleton.
By comparing the resulting 3-D images with CT scans of Khroma conducted at two French hospitals, as well as with modern elephants, the scientists were able to recreate with reasonable certainty how the two animals died, as well as draw more conclusions about how they lived. For example, Khroma’s brain was slightly smaller than a newborn modern elephant, which suggests that the gestation period for mammoths was shorter.
Most notably, the researchers found masses of sediment in the trunk, throat and bronchial passages, indicating that both animals–seeming otherwise healthy–probably breathed in mud and suffocated. Minerals found in Lyuba’s lungs indicated that she probably died after falling into a lake, and might have crashed through the ice during Siberia’s spring thaw, while evidence indicates that Khroma might have fallen into a river and fractured her spinal column. Separately, researchers at the University of Michigan School of Dentistry examined the baby mammoths’ teeth with micro-CT scans. By counting the daily growth layers inside the teeth, they estimated that Lyuba died 30 to 35 days after birth, while Khroma lived 52 to 57 days.
As Fisher tells NBC News, the remains of the two baby woolly mammoths “can be thought of as Rosetta Stones that will help us interpret all the isolated baby mammoth bones that show up at other localities.” His colleague Zachary Calamari, of the American Museum of Natural History agrees that studying Lyuba and Khroma could help them understand future mammoth questions. “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.”