Uintatherium

But She is!

Uintatherium is a huge rhino/bison/fantasy-beast-looking animal nearly as large as an asian elephant who lived in the Eocene, over 40 million years ago, before the similar-looking but distantly related Brontotheres reached their peak. Look her up!

And I tell of the Eocene (though not Uintatherium specifically) near the end of Before the Dinosaurs (the last chapter, Legacy of the Age of Pangaea)!

And by the way, we ARE Theriums- the word means Beast, and is used to describe large mammals!

And yes, she IS a Therium.