Short answers, pulled from the story.
The Ancient Beringian lineage is an extinct archaeogenetic group that inhabited Beringia during the Last Glacial Maximum. This distinct genetic population split from the Ancestral Native American lineage approximately twenty thousand years ago and persisted without significant admixture until the death of USR1 some 8,000 years later.
Archaeologists uncovered the remains of two female infants including USR1 in 2013 at the Upward Sun River site in interior Alaska. The older infant dates back approximately 11,500 years and represents a rare physical link to populations that lived there during the Last Glacial Maximum.
Researchers from the Centre for Geogenetics at the University of Copenhagen's Natural History Museum of Denmark performed the nuclear DNA sequencing on the older infant. Their team published results in January 2018 within the scientific journal Nature after comparing the infant's genomes against both ancient and contemporary human samples.
The Ancient Beringian lineage formed when East Asian lineages mixed with Ancient North Eurasian groups over time before splitting from the Ancestral Native American group. This combination reflects the peopling of the Americas via Beringia during the Last Glacial Maximum and emerged between 20,000 and 25,000 years ago.
The Ancient Beringian lineage is extinct because it does not appear as a contribution to modern indigenous lineages in Alaska or elsewhere. A 2018 study suggests the population was absorbed or replaced by a back-migration of North Native Americans into Alaska before approximately 2,500 years ago.