I'd imagine the excess CO2 would have had some effect on the plants of the time, which (100% guesswork here) may explain the profusion of redwoods, tree ferns and giant horsetails. Obviously any effect on plantlife trickles down through the ecosystem, with herbivores adapting for specific grazing (such as stomach-propelled giantism, perhaps) and predators having to adjust to any differences that caused.
The generally higher temperatures would have had an ecological effect too (if I remember rightly the Triassic, in particular, was very arid, but this had more to do with the landmass organised into the supercontinent Pangaea). It's important to remember though that just because the temperature tended to be higher, it doesn't mean that everywhere was hot. Another point is that the temperature throughout the Mesozoic is actually roughly standard for most of the time there's been complex life on earth - the dips, such as the present one, are associated with ice ages (and we are currently in an interglacial period of an ice age).
If it's true that the Mesozoic had a significantly lower oxygen level, though, then the effect of that on animals would have been enormous. There's a theory that archosaurs and mammals gained a foothold in the late Triassic because they'd evolved more sophisticated respiratory systems, making them able to function at a high level despite the sparse oxygen. Archosaur air sacs (particularly prevalent in saurischians and pterosaurs) and mammalian thoracic diaphragms are far more efficient for respiration than any reptile system, and therefore the latter groups went into decline.
As mentioned earlier though, there's some debate about the oxygen level, whereas the CO2 is more or less a known quantity.
Anyway, Acheroraptor (funny you mention Archaeoraptor, as Philip Currie was involved in the study of both).
It did indeed come after Dromaeosaurus, and you make an excellent point because this is very important for understanding dromie evolution and distribution. The researchers have recovered Acheroraptor as a basal velociraptorine, which makes it the only one ever found outside Asia - and genetically separated from slightly earlier countrymate Dromaeosaurus by a potentially huge gulf of time.
Before we get all excited though, it's worth pointing out that dromie evidence tends to be fragmentary, and Acheroraptor is no exception. Our piecing together of the dromaeosaurid family tree is highly speculative, given that key genera don't even have well-preserved skulls associated with them (notably, the giant Utahraptor and Achillobator, which as early and middle examples of the group, are of key importance). It wouldn't surprise me if the surprise discovery of a complete skull from a little-known animal throws the whole family tree into re-alignment, and Acheroraptor may ultimately prove to be a dromaeosaurine.
