Dinosaurs vanished earlier than previously thought and "within a gnat's eyebrow" of the cataclysmic meteor impact blamed for their extinction, say scientists.
Corrected dates for both events suggest they occurred almost at the same time, around 66 million years ago.
Previous studies have indicated that the impact pre-dated the death of the dinosaurs by as much as 300,000 years.
The disaster was probably the "final straw" for the dinosaurs but may not have been the only reason why the reptiles which ruled the world for more than 150 million years died out, scientists believe.
A 110-mile crater in the Caribbean off the coast of Mexico marks the spot where a six-mile-wide object, either an asteroid or comet, smashed into the Earth.
Clues to the event remain in the form of iridium-enriched dust, glassy spheres and shocked quartz that was spread around the planet.
Scientists used new radioactive dating techniques to determine both the date of the impact and that of the dinosaurs' extinction. The research, published in the journal Science, shows they occurred within 33,000 years of each other.
Lead scientist Professor Paul Renne, from the University of California at Berkeley, US, said: "The impact was clearly the final straw that pushed Earth past the tipping point. We have shown that these events are synchronous to within a gnat's eyebrow, and therefore the impact clearly played a major role in extinctions, but it probably wasn't just the impact."
Dramatic climate fluctuations over the previous million years, including long cold snaps, may have brought many creatures to the brink of extinction before the meteor struck, he said.
The researchers also concluded that the Earth's atmospheric carbon cycle returned to normal within about 5,000 years of the impact. In contrast, it took between one and two million years for the oceans to recover.