The dinosaurs' decline 75-66 Mya may be overstated. The geology is good-enough to mark that, yes, there's an iridium layer. It seems, in North America anyway, dinos were foraging in high-vegetation regions as are still lush today. We've been digging in central Texas, not so lush now and swampy then.
Recall that after 75 Mya the basic northern hemisphere continents look much like they do now. For major differences: Tethys was still open to the Indian Ocean, India proper was southern-hemisphere, and Atlantic was a narrow sea - but none of these much affect this continent here.
The Texans are also meanwhile checking out the Yucatan; they find that the asteroid scoured out a geothermal hotspot. So the fish and shrimp and molluscs, at least, came back. (Not the ammonites tho'.)
This seems to agree with other findings that the dustcloud covered the Amazon and gave it more nutrients. To answer those who might ask "if erosion is a problem in the Amazon now why wasn't it a problem before", the Amazon had quite the headstart.
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