Source: TW
The late Littauer had remarked in her landmark review of chariot petroglyphs:
“One cannot help wondering if, no matter what other ends it may eventually have served, this type of rendering of a vehicle was not first suggested to the artist by looking down into a tomb…”
The petroglyphs she was talking about are from the Poltavka-Sintashta-Andronovo horizons & zones influenced by them. The tombs she was referring to re the chariot burials that appear in the Sintashta horizon & continue to the steppe-I-Ir influenced Shang age of what became China.
The chariot burial is that drawn by von Dewall in from Shang age burial. Thus, it seems that ratha-s depicted in Mongolian steppe are from a time when instead of an actual burial the deceased ratheShTha was commemorated by a petroglyph that resembled the original chariot burial.
Now evidence for that comes from Pamirs enroute to the subcontinent, where on a high mountain there is a funerary site with a chariot petroglyph found by Soviet researchers. The significance of ithyphallic depictions is unclear.
On the other hand in Mongolia we have petroglyphs showing carts/ in profiles (Below Jamani Us, Mongolian Altai).
Other animals in the scenes with peculiar chariot rendering are shown normally in profile. Hence, this “in tomb” was probably a specific convention associated with a funerary rite.