@Pamela Rosa,
This article is kind of a duhh. The base of te Tithonian of the Late Jurassic was defined by the presence of fossils that included several of the mammalian clan (marsupials among em). SO to say we shared ancestry with marsupials of the Tithonian time, is like saying that you are related to your ancestors.
Its anarticle that is written from the school of the bloody obvious. Since mice are placentals, they did , of course arise in the "top of the K".
I wish these papers would not make common knowledge sound like new ****.
Therefore, I too wonder what the agenda of the article is?