Mammoths were not one but two species, that had diverged one million years ago, one of which became extinct c. 45,000 BP, some time before modern humans arrived to their habitats.
Both mammoth species had low genetic diversity, what is curious for an animal that ranged from Europe to North America.
The mtDNA of mammoths was a lot more complex than their elephant relatives, either African or Asian.
They managed to generate and compare 18 complete mitochondrial DNA sequences, a unique feat in the field of aDNA studies. They could make it because they worked with hair, not with bone, what evidences that hair preserves aDNA much better than any bone tissue.