Hi Fons,
If it definitely came from Argentina, one would naturally presume it to be
T. merianae, but, I must admit I've never seen
T. merianae so I can't say yes or no with any real certainty. Sorry. I think there is a Tegu forum, similar to ours (only for Tegus!!), you could try them. theTegu.com
Either way it's a fantastic looking animal. Can I have it?!!