Extinction of the Dinosaurs

Dinosaurs were the the dominant land creatures on Earth for approximately 165 million years.
The first appeared during the early Triassic period (248 million to 213 million years ago), evolved into a variety of different forms, and continued to evolve in new species during the subsequent Jurassic period (213 million years ago to 144 million years ago), and Cretaceous period (144 million years ago to 65 million years ago).
During this era, known as the Mesozoic Era, different species of dinosaurs evolved and died out at different times, but suddenly at the end of this era (a point known as the Cretaceous-Tertiary boundary), all the remaining species of dinosaurs became extinct.
A variety of different explanations have been proposed for the extinction of the dinosaurs.
Some theories however do seem unlikely based on the simple fact that the correct explanation would not only to explain the extinction of the dinosaurs, but why it was so sudden, and why a wide variety of other animals (both land-living and marine animals) died out at the same time.
Based on this criteria, theories such as dinosaurs died out because mammals ate their eggs, or that dinosaurs auffered hallucogenic effects from eating angiosperms (flowering plants which first evolved in the Cretaceous), are perhaps somewhat implausible.
Currently the most favored explanations for the mass extinction are either volcanism or the impact of an asteroid.
Supporters of the volcanism theory point to the Deccan Traps in India, where massive vclcanic activity appears to have occurred at about the right time in history - and would no doubt have caused wide-ranging ecological effects all over the Earth.
Supporters of the asteroid theory point to a layer of iridium which is found all over the world in rocks dated to the end of the Cretaceous, as well as plausible candidate for the asteroid's impacr crater in southern Mexico.