Thanks Rohit I am attaching a notebook which compares the PlotMarkers used with "Automatic" and those obtained from Graphics`PlotMarkers[]. I am using the PlotMarkers from this code

{filledcircle, filledsquare, filleddiamond, filleduptriangle, 
   filleddowntriangle, circle, square, diamond, uptriangle, 
   downtriangle} = Graphics`PlotMarkers[][[All, 1]];

The appearance of the "Automatic" PlotMarkers is quite different from the appearance of those obtained as above, Also note

Head[filledcircle]
*String*
Head[Graphics[Disk[]]]
*Graphics*

It would be so much better if there were the equivalents of Disk[] and Rectangle[] for the other shapes.