Uncle Allotheria?

In the song ‘Mammal’ by They Might Be Giants, they mention various classes of mammals. I know what placental, monotreme and marsupial mammals are, but what on earth is/was an allotheria? I’ve not been able to find anything on it anywhere. And it’s bugging me!

http://www.sinc.sunysb.edu/Stu/bburger/MainPage.html#Multituberculates

http://www.tmbg.org/band-info/faq/#q26

In the interest of splitting the last possible hair, there is a hint in the song:

“…dead uncle Allotheria…”

So, it comes down to the shape of a tooth? I was hoping for something a bit cooler than that. I don’t know what sort of new method for reproduction you could come up with – maybe like amphibians, you know, eggs in the water, all that good stuff. Or, having the kid emerge from a place on the body that doesn’t make sense – like the forehead, ala mythology.

Just thought that it might have more to do with reproduction, given the other three types named.

Infraclass Allotheria is equal to Order Multituberculata. Multituberculates, as everyone knows, are “the little mammals that could” – the group of Mesozoic mammals that survived the extinction of the dinosaurs and hung in there for another 20 million years or so.

They were gnawing fruit and seed eaters, and were finally driven to extinction by the burgeoning Rodentia.

Apropos of songs about mammals, the Canadian National Museum has a wonderful video for kids on mammals with a bilingual soundtrack, the English “I’m a mammal and so are you” or the French “Nous sont tout de mammifere” (which sounds ungrammatical but that’s what they sing – Quebecois dialectal usage?).