In the Wikipedia article for the Simpsons Desert in Australia in the first paragraph it says:
It is the fourth-largest Australian desert, with an area of $\small\mathsf{176,500}$ $\small\mathsf{km^2}$ ($\small\mathsf{68,100}$ sq mi) and is the world's largest sand dune desert.
Simpson Desert - Wikipedia
I know that the Rub' al Khali Desert is the largest sand desert in the world, and as seen in this photo it has sand dunes:
This is the Rub' al Khali. The caption for this picture on the article says "Sand dunes to the east of Liwa Oasis".
Here is another photo of the Rub' al Khali
Is it the case that although the largest sand desert is in southern Arabia and contains sand dunes nevertheless there is another larger "sand dune desert" in Australia? How is this classified? I'm assuming if this is true it means that the Rub' al Khali Desert doesn't fall into the category of a "sand dune desert", whatever that is.
I've seen photos of both and both look very sandy and duney to me.
12:35:53
, Wikipedia updated13:13
Good work! $\endgroup$