The species for which revival is technologically plausible are those with well-preserved frozen specimens, mainly pleistocene (mega)fauna like mammoths and the

The species for which revival is technologically plausible are those with well-preserved frozen specimens, mainly pleistocene (mega)fauna like mammoths and the lions presented here. They lived at most a few tens of thousands of years ago, which is geologically barely worth mentioning, and the atmospheric composition hasn't changed much since then, or not in ways relevant to animals.