The scans also revealed that just before death Lyuba had inhaled bits of mud typically found at lake bottoms.
She also had signs of a response called the mammalian dive reflex, reflected in high levels of a mineralized form of iron phosphate in her face and brain tissues. When facial skin and muscles are exposed to cold water, particularly in babies, the body prepares for oxygen loss by shunting more blood circulation from the heart to the brain. This reflex allows the brain to survive longer without oxygen when the body is submerged under water. The iron phosphate formed over the months and years after her death when phosphate leached from her bones and mixed with iron in her blood.
The analysis paints a terrifying picture of Lyuba's last moments. The baby mammoth was likely crossing a frozen lake with her mother when she crashed through the ice and did a "face plant," into the muddy lake bottom, Fisher said.
She then got mud stuck in her airways and tried to blow it out of her trunk. Because the nasal passages narrow in the trunk, she only managed to get the mud stuck even more.
"It moved straight into her trachea and bronchi and by that time she was too exhausted and couldn't clear her airway," Fisher told Live Science. "It was just a matter of minutes before she would have lost consciousness."
Khroma was also healthy when she died, with a belly full of undigested breast milk that looked like fresh yogurt.
Because Khroma was partly eaten, researchers have to do more speculation to understand her death, Fisher said.
But Khroma had a broken back and mud from a fast-flowing river in her trachea.
So it's possible Khroma was standing on a riverbank when it collapsed, leading her to fall, break her back and be buried in a slurry of mud that she inhaled while trying to extricate herself, Fisher said.
In addition to painting a grim picture of the mammoth calves' last moments, the research also provides some insights into how they developed.
For instance, Khroma's brain was smaller than a newborn elephant's brain, suggesting mammoths may have had a shorter gestational period than modern elephants, Fisher said.
The findings were published July 8 in the Journal of Vertebrate Paleontology.
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