I read this in the 1980s or early 1990s. However, I don't know how old it was at that time. In the book Earth is visited by a large cylindrical spaceship (think L5- or Rama-like living space) inhabited by evolved dinosaur "humanoids" in one half and unevolved Jurassic era dinosaurs on the other half separated by a giant wall. It is not the book Toolmaker Koan as the plot description is different. Also, in Toolmaker Koan from what I can tell the evolved dinosaurs were technologically advanced whereas the evolved dinosaurs in this case were stone-age level technology or so. I have also read and confirmed it is not Day of the Dragonstar by David Bischoff nor Homecoming by Barry Longyear. It is not West of Eden by Harry Turtledove as it occurs in space.
PLOT DESCRIPTION In the story, an Earth delegation visits the spaceship to speak to the evolved dinosaur humanoids. A number of scenes in particular stand out on the visit:
In a humorous bit, as part of the delegation there is a famous SF novelist/author that visits the ship. Unfortunately for his reputation he gets drastically spacesick on the way up. Of course, he works to try and hide this from his readers as it would not do for them to learn he can't handle space travel.
Even worse for his career, as the SF author is speaking to the evolved dinosaurs one of them suddenly goes crazy, reaches over and bites his head off.
At that point, suddenly the ship takes off and leaves Earth orbit/vicinity. A male pilot and a female passenger (paleo-biologist maybe?) who were flying over the unevolved dinosaur portion of the spaceship (ultralight or other small plane?) suddenly get jolted enough to crash. They have to work their way back to the safe side of the wall as the phrase went "Edgar Rice Burroughs Tarzan like". I think the criticism was because the female biologist had her husband/boyfriend/fiancé on the ship as well and there was a rather tense scene when they arrived back and he learned she had spent all that time with the pilot.
As I recall, the story actually ends with the delegation trapped and moving away from Earth with no way to return.
The delegation has to start electing leaders to help negotiate with the evolved dinosaur humanoids which also seem to simply be trapped.
I know for sure this is not the Rama series as I am very familiar with the plot on that. Nor is it the other books I mentioned.