I approach the dais, and having gained the lectern, address the assembled dinosaurs through a truly enormous PA system that I have brought back in time with me. It is run by a huge generator that I also brought back with me. It's a really big time machine, okay? Moving on. I speak thusly:
"My fellow dinosaurs, and, by "fellow" I mean in the very loose sense of the word that all living things are interconnected, on this most auspicious of days, with so many of our brethren having already been killed by the concussive shockwaves, massive walls of heat and/or super-tsunamis created by the sky-rock's impact, I come to you from the future.
"I represent a race of creatures who have only very recently started evolving in your midst. Right now, we are a small furry mouse-like species, too tiny for most of you to see. I speak to you as one who has knowledge of your ultimate demise. The sky-rock dust will cloud the planet and darken the ground, killing off most vegetation and leading to your extinction in comparatively short order.
"I speak to you as a future citizen of this same planet which, in my time, also faces massive climate change. I say to you that you must adapt your ways. Adapt now or face certain annihilation.
"Imagine, if you will, a world where no more of your kind survive. Indeed, I have the knowledge that you do not want to hear: you will all die. My kind, in about sixty-five million years, will begin to dig your remnants from the soil. You do not exist any longer. Your demise leading to a chain of events which allow my kind to discover this cruel trick of nature called extinction.
"There is hope! Back in time, I have travelled to say that, if you change your ways, you may survive, and we humans will never need to discover your tragic fate. In fact, it is likely that avoiding your extinction in these trying times will leave you the dominant creatures on this planet for the distant and indeterminate future; as you would surely prevent the evolution of many other forms of life due to your position in the food chain... and... and... ohhh...
"uhhh... welllll.... hey, look at the time... wow, I think I've said enough... to sum up, ummm... looking good dinosaurs! Just, uhhh... go about your daily business as always.
"Thanks for listening."
I back away from the lectern nonchalantly, hop into the time machine and depart for the exact same time and position from which I had left.
Years later, paleontologists on a dig for stegosaurus fossils, are shocked to find a mineralized PA system and generator in a layer of rock dating back sixty-five million years.
[Here's what I might have suggested to the dinosaurs, had I finished the spech as written.]