Theria
In our world, Theria denotes both Marsupials and Placentals. In Different World, it only refers to marsupials, the only possible evidence for placentals being a poorly preserved fossil, possibly of HE first placental Eomaia in the Yixian Formation. It's more than possible they went at KT, alongside multituberculates, Gondwanatheres and Prestosuchids. Very sketchy evidence that could be attributed to placentals, but could easily be marsupial in origin, suggests that remnants may have outcompeted by Triconodonts.
Nevertheless, marsupials did survive to the modern day, though in remarkably less success than ours. The abundance of reptilian competition and the diversity of their allotherian adverseries have left them in mostly small niches in Australia, as detailed by the Kangarats and Roorats. The greatest marker of their potential is marked by several of the Oceanic Isles, where they are the only mammals, and the only true terrestrial chordates, sharing with a few birds, allotherian notabats, and a couple of species of Coelurosauravid. Otherwise, they are greatly restricted. Odd in this world that the fortunes of Sphenodonts and Marsupial seem almost reversed.
Nevertheless, marsupials did survive to the modern day, though in remarkably less success than ours. The abundance of reptilian competition and the diversity of their allotherian adverseries have left them in mostly small niches in Australia, as detailed by the Kangarats and Roorats. The greatest marker of their potential is marked by several of the Oceanic Isles, where they are the only mammals, and the only true terrestrial chordates, sharing with a few birds, allotherian notabats, and a couple of species of Coelurosauravid. Otherwise, they are greatly restricted. Odd in this world that the fortunes of Sphenodonts and Marsupial seem almost reversed.