As I discuss in this question, when a mantra is given in the Puranas, it is usually preceded by a Dhyanam, which describes the appearance of the god whom you're supposed to meditate upon before reciting the mantra. For instance, in my profile page I quote the Sri Vishnu Stuti, which is part of the Dhyana shlokas of the Vishnu Sahasranamam, and in my question here I quoted a Dhyanam for another Vishnu mantra. Now I'm interested in another Dhyana.
In this excerpt from the Narada Purana, a Dhyana shloka is given for a Ganesha mantra:
He shall offer six hundred to Ganesha the lord of words (Vak) who is possessed of his consort riding on an elephant and whose hands shine with noose, goad, the vessel of nectar and sweets.
My question is, why does the Narada Puranas describe Ganesha as riding an elephant? Ganesha is usually described as mushika-vahana, the one who rides on a mouse.
Now I have found pictures of Ganesha riding on an elephant, like this:
But are there any scriptures that describe him riding an elephant, and/or discuss who this elephant is?