Just so you know, there is some debate over whether
Purgatorius is an actual primate, and even if it was, it probably resembled a modern
tree shrew more than a lemur or other familiar primate.
Also, true rodents may not have evolved until after the K-T extinction, although there was a group of chisel-toothed mammals called multituberculates, which probably filled the same ecological niches. There were also opossum relatives such as
Alphadon, and shrews or shrew-like creatures, some of which may have had a venomous bite.
It is possible that there were bats in the late Cretaceous, though there is no more evidence for them being present than there is for rodents. Given that effectively modern bats existed 52 million years ago, they must have evolved much earlier. If the most primitive known bat,
Onychonycteris, is anything to go by, then Mesozoic bats probably would have been unable to echolocate, had claws on all five fingers and relatively long tails, and generally flew only short distances. I also read
one study that proposed that the first bats were diurnal and ate mainly fruit (as well as insects). However, it’s mostly informed speculation, so if you decided to feature bats in your story, you could portray them as nocturnal, bug-zapping echolocators if you wanted.
Okay, better ask another question…Have you heard about
Sanajeh indicus? It's a Mesozoic snake found fossilized with a sauropod nest; apparently it was preying on the eggs and/or hatchlings.
