Stolarek et al: Genetic history of East-Central Europe...

[Dewsloth]

My hopes for identifying an ancestral source for RFK263 got a little complicated
In the supplements for the paper published today: "Network of large pedigrees reveals social practices of Avar communities"
https://www.nature.com/articles/s41586-024-07312-4#Abs1
https://static-content.springer.com/esm/...M1_ESM.pdf
RKF263 does not seem to be dated, but is assigned as "Sarmatian" - which seems to be his autosomal summary, despite his YDNA.

So what tribes are present in the pre-Avar period with the Sarmatians?  Probably the Quadi, but plenty of other candidates get mentioned just in the beginning paragraphs of the supplement (although Langobards might be too recent for him to melt into the autosomal background):

Population shifts in the eastern Carpathian Basin, c. 300-800 CE
The DTI and TT regions, east of the Danube, never were part of the Roman Empire, which had
conquered the western part of the Carpathian Basin west of the north-south tract of the Danube, around
the turn of the era, and established the province of Pannonia which remained under Roman control for
almost half a millennium. In the course of the 1st century CE, a large group of Sarmatians occupied the
eastern half of the Carpathian Basin. The Sarmatians, who spoke an Iranian language, had largely
replaced the Scythians in the steppes north of the Caucasus and the Black Sea in the 3rd/2nd centuries
BCE. In the Carpathian Basin, they remained a regional power, and often operated in close conjunction
with the Germanic Quadi who lived in what is now southern Slovakia. Roman observers noticed that
the two peoples had come to resemble each other to a considerable degree, although the archaeological
evidence only confirms this in the contact zone7–9. In the course of the 4th century, the Sarmatians had
to face the threat from Goths and Gepids from the east and north-east, and from Vandals who expanded
south from their homelands north of the Carpathian Mountains.
The situation in the Carpathian Basin changed in the aftermath of the arrival of the Huns, who came
from somewhere in Central Asia to Europe in 375 CE. Goths, Alans and other groups moved west, and
some of them settled in the Carpathian Basin. In c. 400, the Huns occupied the Carpathian Basin10. Most
Vandals and Alans and some Gothic groups left and marched as far as Italy, Spain and North Africa.
Many Sarmatians stayed in the TT and also DTI regions, and Ostrogoths, Gepids and others also
remained under Hun rule. In the 430s, the short but dramatic story of the Hunnic Empire began, which
reached its apogee under their legendary king Attila, who first devastated large parts of the Roman
provinces in the Balkan Peninsula, and then organised two large military expeditions into Gaul (451)
and Italy (452), at the head of an army which included several, mostly Germanic-speaking peoples11.
We have a lively report from a Byzantine diplomat who visited Attila’s wooden palace somewhere
between Danube and Tisza, a rich and bustling cosmopolitan power centre.
Attila died in 453, and his empire collapsed in a series of conflicts between his sons and the subject
peoples. The Hun realm dissolved into a number of smaller kingdoms, of which the Gepid kingdom in
the TT region was the most durable12. The Goths dominated Pannonia until they left for a more
profitable future in the Roman Empire. In the southern DTI, a small kingdom of the Sarmatians
emerged, and further north, one of the Sciri; north of the Middle Danube, kingdoms of the Suebi and
the Heruls existed for a generation or two. Other groups, often mixed between Huns and other groups,
joined Roman service in the Balkan provinces immediately after the fall of Attila’s kingdom. Some of
Attila’s sons with their following tried to carve out their own realms, but mostly retreated to the steppes
north of the Lower Danube and the Black Sea. In the 6th century, Longobards moved into Pannonia,
where they began to challenge the Gepids, their eastern neighbours. In 567, they destroyed the Gepid
kingdom. In the following year, they united a large following of many groups still living in the
Carpathian Basin (reputedly Gepids, Bulgars, Suebi, Sarmatians and Pannonian provincials) and
invaded Italy, where they founded their kingdom.
This is when the Avars came to the Carpathian Basin. They had arrived north of the Caucasus in 557,
and immediately sent an embassy to Constantinople to offer an alliance to the Byzantine emperor.