Jeff Hecht writes: "It is curious that living birds seem to have originated well before the K/T, in contrast to mammals."
If you'll forgive the Linnaean vernacular, I think that Jeff Hecht meant to say something along these lines: "It is curious that extant orders of birds seem to have originated well before the K/T, in contrast to extant orders of mammals."
That's even less curious than my interpretation (that he meant "placentals" instead of "mammals"), since it's essentially meaningless. "Order" doesn't have a good definition, but, when it comes to birds and mammals, you almost could define it as "any of certain clades originating in the early Cenozoic or Late Cretaceous".
-- Mike Keesey