Hi Filiberto,
I can’t say that I see clearly the analogy of the «pregnant animal» rugs found in Tibet with 19th century Avar kilims & rugs
. I like both though.
The rug fragment shown in your post is too small to tell, but could be a close cousin of the other «Kircheim rug» below, already shown in Turkotek by Marla and others.
Dated by C14 the latter was found roughly contemporaneous with the 12th-13th century «pregnant animals» rugs. If I do not err, this impressive piece (which according to Kircheim and al. might have been woven south of the Caspian), was exfiltrated from Tibet too.
Although it is full of nice little beasts and features two large human-faced «snakes» or «dragons», it’s motifs are very different from those of the "pregnant animal rugs. They seem religious and pre-Islamic to me. Perhaps inspired by an old Indo-European religion? The Mazandaran province for example was penetrated by Islam quite late (directly by Shiite Islam, I believe). Fire-worshipers’ temples were still active southwest of the Caspian Sea until the end of the 19th century.
Best
Pierre