The Etruscan and the proto-Illyrian were J-Y15058, right?
https://www.yfull.com/tree/J-Y15058/
I'd like to opine, assuming that YFull age estimation, samples dating and hgs assignments are accurate. I'm not aware of a reason to doubt it.
The Etruscan would have lived between 2600 and 2700 years ago. The proto-Illyrian, between 3520 and 3620 years ago.
The TMRCA is 3900 years before present, however, it must be read as 4400-3500 ybp, which is the CI 95%. The actual TMRCA may be then a bit closer or farer in time, naturally, meaning the common ancestor of them probably lived between 800 and 1800 years before the Etruscan and 0-900 before the Illyrian. However, Y15058 SNP has four equivalents. I wonder if the Illyrian was confirmed positive for all. Being younger than the TMRCA doesn't necessarily mean that that specific line thrived*. If not, the TMRCA between the Etruscan and the Illyrian would be slightly different (older), and so the CI 95%. I continue this post assuming the Illyrian was a "complete" J-Y15058, to simplify, since I don't have details on his exact categorization, but also because the equivalents involved are just few.
"If" the actual TMRCA is closer to the later limit, then it would appear far more likely that ancestors of this Etruscan individual (not necessarily "the Etruscans") did live around present day Croatia ~3500 years ago, migrating anytime after that. Speculating when approximately it left Balkan, and from where it must have arrived, would be another story, which demands a knowledge I don't have. On the other hand, if the actual TMRCA is closer to the earlier limit, then we'd be talking on a relevant time window for dispersal, making more difficult to speculate on the place of the common source.
We obviously don't have a definitive answer, but it seems to me that the possibility proposed (patrilineal ancestors of that Etruscan individual living in the other side of Adriatic Sea certain time before) deserves to be considered.
*Side note not that important neither directly related:
- The extinction of a given lineage could have happened anytime after sample's time, including way after the TMRCA of the related survivor lineage.
- These old samples usually have low coverage, however, when coverage allows, a supposedly extinct lineage would be well evidenced in general by an ancient sample being positive and negative for some SNPs that defines the related survivor lineage and being positive for SNPs not shared with this survivor lineage. How close this hypothetical extinct lineage is from the survivor lineage would be especially relevant, but it may be difficult to know it, due to the usual low coverage.
- The condition of an ancient sample way older than the TMRCA of the lineage being positive for some SNPs and negative for other SNPs that currently define it, while proves a "pre-hg", doesn't necessarily prove per se the lineage went extinct, i.e., that it's not direct ancestral to moderns. Of course, finding the remains of such old direct ancestors doesn't seem likely, but...
- There are some well developed lineages in regards to phylogeny, but also the "underdeveloped" ones, due to undersampling and/or rarity, that's why I used "supposedly extinct". We've old branches still to be developed, so in theory what is a pre-hg today could be an hg tomorrow.
- Finally, of course: I'm especially talking about hgs currently defined by several equivalent SNPs.