In a paper entitled "Yamnaya Groups and Tumuli West of the Black Sea", Volker Heyd made this comment regarding the orientation of bodies in the Western Yamnaya:
"The position of the body in the [Yamna] grave pit is typically supine with the flexed legs...Flexed legs are often still upright, even after thousands of years in the graves, but may have also fallen to one side due to decomposition of the body tissues. Also, the so-called frog-position of the legs might be due to this process of decay."
|Male Archer looking East. Samborzec, stanowisko 1, grave 3 (Makarowicz)|
The legs of grave 3 may have originally looked like this, which is how Yamna people were buried.
So now the fun part. What does this mean? Z2103 is now in two Beaker graves I2787, I7044 from Szigetszentmiklos and I4253 from Samborzec. A man at Samborzec appears to have been buried with a mixture of Beaker and Yamnaya rites. But what does the phylogeny mean in light of this?
One way to look at this is that there is a clear sign of a founder effect heading West. Looking strictly at the phylogeny of R1b, and not taking anything else into consideration, this of course makes a lot of sense. That solves it for a lot of people. But extrapolating geo-phylogeny on an archaeological culture can be a problem when the two are in apparent disagreement.
Another way to look at it (until Western kurgans prove or disprove the presence of L51/P312) is that in the highly heterogeneous border outpost of the Csepel populations (and by extension the closely related Samborzec community), Bell Beakers and Yamnaya, confusingly, actually mixed to a small and unimportant degree.
Within these old Beaker cemeteries of Békásmegyer, Budakalasz, Szigetszentmiklós, Bell Beakers appear as a minority that increases but it is clear that there are different peoples mixing at these sites and that mixing is a cultural trajectory away from Bell Beaker.
I2787 at Szigetszentmiklos could be a red herring or it could provide a connection. While it's obvious Beaker is paternally related to Z2103 and shares a similar ideaology, and while a bunch of scenarios and chronologies are possible, drawing straight arrows from one to the other is an over-simplification or wrong.
But in any case, this one grave is an interesting one with mixed traits.