On Jul. 11, 2024, a team led by scientists from Baylor College of Medicine, University of Copenhagen, and Centre Nacional d’Anàlisi Genòmica and Centre for Genomic Regulation reported discovering fossils of ancient chromosomes in the remains of a woolly mammoth that died 52,000 years ago. The fossils preserve the structure of the ancient chromosomes down to the nanometer scale – billionths of a meter. The discovery is featured on the cover of Cell.

Fossil chromosomes are a powerful new tool for studying the history of life on Earth. That’s because typical ancient DNA fragments are rarely longer than 100 base pairs, or 100 letters of the genetic code – far smaller than the full DNA sequence of an organism, which is often billions of letters long. By contrast, fossil chromosomes can span hundreds of millions of genetic letters.