During the Mesozoic era, the dinosaurs occupied most of the “big-animal” niches – there were not many roles for mammals except as small insectivorous rodent-types who scurried away to avoid getting stomped on by their gargantuan reptilian overlords! Or, at least, that is the way things were depicted when I read my dinosaur books as a child way back in the 1960s and 1970s. Have they found more mammalian fossils in the ensuing years? Somebody please bring me up to date on how Mesozoic mammals are currently viewed. Any info would be appreciated!
This came up a couple of years ago in another thread. I repeated what I’d read (I forget where) that all the mammalian fossils discovered could fit in a shoebox – a testament to their rarity and their small size. Every Mesozoic mammal fossil(not pre-mammalian precursors, some of which were huge); I’;ve ever seen has been minute – usually a jawbone.
It was pointed out to me, IIRC, that there have been a lot more mammal fossil finds, but the statement’s probably still true.
My information is well out of date in this area, but there are some details on larger Mesozoic mammels here as a starting point. In general most sources seem to suggest they were small, with R. giganticus as an exception.
Hopefully one of the experts will be along with more information soon.
The largest known Mesozoic mammal is Repenomamus giganticus, discovered a few years ago. It was the size of a small dog, about 3 feet long and 30 pounds.