Finding. Medieval Europe did not buy all its walrus ivory from Norse Greenland. That story came from sampling decorated rostra, the skull-and-tusk packages. Workshop offcuts from Sigtuna, Sweden, tell a different trade. Using a genome-wide west-versus-east Atlantic walrus split and 144,986 diagnostic nuclear SNPs that still work on low-coverage historical DNA, every medieval rostrum still goes west. About half the Sigtuna ivory goes east, to Iceland and the Barents Sea, and those eastern pieces come first. Mitochondrial DNA alone could not see this. The ivory trade was sequential and wider than the rostrum trade.
Why this paper matters
This is not a bioenergetics paper. It is on the desk because Mito.news indexes mitochondrial genomes, and because the prior error was an mtDNA-plus-sample-type error. If you only sequence the objects that were fashionable to keep intact (rostra), you reconstruct a Greenland pipeline. If you sequence the debris of a workshop, you recover Barents and Iceland ivory that historical texts already mentioned and earlier molecular work missed.
The methodological payload is the nuclear SNP classifier. Mitochondrial DNA is necessary and insufficient for this split. That is a useful sentence for anyone still provenancing historical tissues with mitogenomes only.
What they actually measured
They resolve genome-wide trans-Atlantic walrus structure, find significant nuclear differentiation west versus east, then apply 144,986 spatially diagnostic SNPs to low-coverage historical rostra and tusks. Result: medieval rostra all western; half of Sigtuna ivory eastern; eastern objects earlier than Greenland-associated ones. Sequential exploitation, broader Arctic ecological globalization.
Sigtuna is one site. The paper is not a census of European reliquaries. It is a proof that sample class and marker class both matter.
How to read the score
Low seventies as an ancient-DNA brief, low sixties as organelle biology (which it is not). We keep a 70 because the corpus includes mtDNA provenance and the result rewrites a cited molecular-archaeology claim. Confidence is medium-high for the Sigtuna contrast, medium for the Arctic-wide implication.
What to do with it
If you provenance historical pinniped tissues, stop using mtDNA alone and stop treating rostra as a random sample of ivory. Pull the SNP panel. If you came for mitochondrial disease or OXPHOS, move on. The directional implication is that medieval Arctic extraction hit the eastern Atlantic first and that Greenland rostra were a later, different commodity.