Population genomics of post-glacial western Eurasia.

Western Eurasia witnessed several large-scale human migrations during the Holocene <sup>1-5</sup> . Here, to investigate the cross-continental effects of these migrations, we shotgun-sequenced 317 genomes-mainly from the Mesolithic and Neolithic periods-from across northern and western Eurasia. These were imputed alongside published data to obtain diploid genotypes from more than 1,600 ancient humans. Our analyses revealed a 'great divide' genomic boundary extending from the Black Sea to the Baltic. Mesolithic hunter-gatherers were highly genetically differentiated east and west of this zone, and the effect of the neolithization was equally disparate. Large-scale ancestry shifts occurred in the west as farming was introduced, including near-total replacement of hunter-gatherers in many areas, whereas no substantial ancestry shifts happened east of the zone during the same period. Similarly, relatedness decreased in the west from the Neolithic transition onwards, whereas, east of the Urals, relatedness remained high until around 4,000 BP, consistent with the persistence of localized groups of hunter-gatherers. The boundary dissolved when Yamnaya-related ancestry spread across western Eurasia around 5,000 BP, resulting in a second major turnover that reached most parts of Europe within a 1,000-year span. The genetic origin and fate of the Yamnaya have remained elusive, but we show that hunter-gatherers from the Middle Don region contributed ancestry to them. Yamnaya groups later admixed with individuals associated with the Globular Amphora culture before expanding into Europe. Similar turnovers occurred in western Siberia, where we report new genomic data from a 'Neolithic steppe' cline spanning the Siberian forest steppe to Lake Baikal. These prehistoric migrations had profound and lasting effects on the genetic diversity of Eurasian populations

Ytterholmen revisited - implications for the Late Wenlock stratigraphy of Gotland and coeval extinctions

The latest Cyrtograptus lundgreni graptolite Chron (Late Wenlock, middle Silurian) is characterized globally by the Mulde Event faunal extinctions and glacio-eustatic sea-level change. Only in the last decade has it been recognized as one of the most severe extinction events of the Silurian Period. A section spanning the Slite Group-Halla Formation boundary on the islet Ytterholmen off main Gotland (Sweden) is unique in that strata through the extinction interval are preserved within a reef complex. The importance of Ytterholmen is twofold: First, based on conodonts, lithology and stratigraphic boundaries, the stratigraphy of the Slite Group-Halla Formation boundary interval on eastern Gotland is now fully understood. in ascending, order: Slite 'g' (c. 12-20 m), Atrypa "reticularis" Beds (c. 0.5 m), Frojel Formation (c. 0.5 m), and the Halla Formation. The boundary between the Frojel and Halla formations is an unconformity as previously reported across most of the main island. Second, correlation of the Ytterholmen section with the Mulde Event reference profile on western Gotland for the first time enables study of this event in very shallow interior areas of the carbonate platform. Here, the c. 1 m thick extinction interval (including the Atrypa "reticularis" Beds and the Frojel Formation) is characterized by mass-occurrences of an atrypid brachiopod, deposition of fine siliciclastic material and termination of the reef complex. Correlation with the East Baltic and Podolia, Ukraine, suggests that similar reef termination occurred contemporaneously throughout the basin. Small patch-reefs occurring immediately above the unconformity on Ytterholmen are among the earliest Mulde Event post-extinction reefs reported from the Baltic basin