Found this interesting comment on page 686
60:1:11 Several million years later the first mammals appeared. They where non placental and proved a speedy failure; none survived. this was an experimental effort to improve mammalian types, but it did not succeed on Urantia.
Not certain how to account for this in my mind – more like some sort of intervention or some student experiment or?? Do you think the Life Carriers would get involved with something like this?

