Emergency excavations by archeologists in Narges Tepe, located in the northern Iranian city of Gorgan, led into discovery of a grave belonging to 3000 years ago containing skeletons of a mother and her infant as well as a dog and its whelp. Archeologists at Narges Tepe have also been able to unearth a grave containing the skeleton of a man buried while sitting on his horse.
... expecting more info further down, there is only:
Abbasi also said that the skeletons of the man and his horse which were found in another grave in the same area belong to the first millennium BC as well.
In the spirit of Adrienne Mayor, I can't help but wonder whether a burial of this sort is what led to the idea of centaurs (as opposed to the usual 'Scythian horsemen' hypothesis). Has anyone collected references to man-on-horse burials?