SOLVED. Two time-travelers in the time of the dinosaurs encounter sentient aliens that can use both dinosaurs and men as host animals. These aliens will become the ancestors of the common cold. Early-to-mid-nineties, paperback, probably American.

[slauderdale]

This book was an English language, probably American, science-fiction paperback published in the early to mid-nineties, which is also when I read it. I think it was a one-off. It’s not a thick book, probably in the 250-350 page range. I don’t remember the cover at all, but it probably had dinosaurs. It’s about two men who go back in time. The way they do so is a government-funded and intentional experiment with time travel. The time machine was invented by a woman scientist and I think it functions by being dropped in some way. The men *may* have been deliberately going back to investigate the mass extinction event that killed the dinosaurs.

The men are not surprised to encounter dinosaurs. But what *does* surprise the men is that there are also these strange life forms, aliens (possibly Martians) that are effectively large sentient viruses. They have the ability to “possess” the dinosaurs, and the men, by entering their brains and taking over their bodies. Initially they do this to gain knowledge and thereby communicate with the men – after they had gone inside the men they go back into the dinosaurs and use the dinosaurs to talk and interact with the men. The aliens are not overtly hostile but the two men realize that they are nonetheless a threat – the aliens now know that there is an extinction event approaching. They had already escaped whatever problem they were escaping on their home planet by going to Earth and using the dinosaurs as hosts; now they intend to escape this new disaster by possessing the men and traveling to the present to the present, where they would be able to use humans as hosts and basically enslave the human race.

It’s possible that the men themselves trigger the actual extinction event deliberately as a way of preventing this from happening. I’m foggy on this part. Some very specific things I do remember, though:

1. The POV character is white and his colleague is black. After one of the aliens has been inside the main character’s mind it asks him some racially based questions and/or uses an offensive term that horrifies the main character, who is appalled at the racist dreck floating around in his own head which the alien had picked up on without really understanding what it had picked up.
2. Changing the past preserves but at the same time changes the future. It also seems as if Time Itself wants things to play out a certain way, and now that things have happened as they have, it doesn’t want them to be changed. So when the main character tracks down the woman scientist who had created the time machine in the original timeline, he finds that she had been raped some years before and became a shut-in, and therefore never did the research that led to the creation of the time machine.
3. The main character’s own memories of how things went down start to become fuzzy, but he still has the journals he’d been keeping in the other timeline?
4. Also the main character believes that the extinction event didn’t really kill off the aliens, because they probably evolved into what is now the common cold, for which there has never been any one effective remedy.

Overall tone:
This was in fact a serious book, with big problems if the men don’t stop the aliens from time-traveling to the present and enslaving humanity.

[slauderdale]

Never mind, I found it. End of an Era by Robert J. Sawyer. I Googled the search string

"paperback" "dinosaurs" "aliens" time-travel

found the book, and then found an edition with a cover that I remembered.
https://www.goodreads.com/book/show/1...

[slauderdale]

Incidentally, I was wrong about it being American: it’s Canadian.