What are the species of methanogens that thrive in the human gastro intestinal tract?:confused:

Erm, Why did you put this in archaeology? Getting it moved to biology...

This paper seems to describe exactly what you're looking for in the abstract:
SpringerLink - Journal Article (http://www.springerlink.com/content/j0525850l400q263/)

It states in the abstract that Methanobrevibacter smithii is the predominant methanobacteria in the feces samples that they analysed (on a Mediterranean diet). A quick Google search of this species brings up a few more sources that state the same thing.

Here's a picture of the little guys: Methanogens Photo Gallery - Methanobrevibacter Smithii (http://www.wadsworth.org/resnres/bios/macario/Methanobrevibacter_smithii.html). Now you know where farts come from!

The paper is $32, so you're probably better off trying to get ahold of it through your library if you want more information. They might have to order it in. Ask for the journal.