If you're old enough to remember the early seasons of the Simpsons, you'll probably remember an exchange between Principal Skinner and an unusually exasperated Apu. Here it is in all its glory.
The joke is that Principal Skinner is hopelessly out of touch, both in not being aware of Jurassic Park, (this was in the 90s remember) and thinks the title Billy and the Cloneasaurus, is a good title and that this qualifies as a great American novel.
Apu does an excellent job of bursting Skinner's bubble, it's a terrible idea in direct competition with a financial and cultural juggernaut in its prime. However, at no point in his tirade does Apu cite copyright, that is because you cannot copyright an idea. Despite the existence of Jurassic Park, Skinner is free to write a novel or a script or a comic or any other format he chooses about a futuristic theme park where Dinosaurs are brought back to life through cloning experiments. The concepts of Dinosaurs, theme parks and cloning are all fair game, he would get some opposition if he titled his masterpiece Jurassic Park over trademarking, but that would have to playout in the courts titles and names aren't protected as such which is why there so many films with Exorcist in the title.
If Billy and the Cloneasuarus either got to a stage where it could be published, Skinner would enjoy the experience of trying to find an agent and a publisher, who almost certainly would strong-arm him into changing the title to anything more marketable. The concepts themselves are fair game, anyone can make a movie about an aggressive Alien life form attacking the crew members, Alien knockoffs are quite common, The Raid, and Judge Dredd, both feature a police officer locked inside an apartment complex controlled by a ganglord and have to fight their way to the top, and both are excellent action movies to boot. Both were released without a lengthy and exhausting legal battle between each others owners over IP rights.
So, you might be wondering what exactly does copyright, well copyright. It's the story, the specific story and its combination of concepts, characters and events and the point of view of that author. You make your own story up on the same premise, you're just not allowed to actively copy an existing work and pass it off as your own. So, to take a hypothetical example Billy and the Cloneasaurus, Billy the young protagonist gets to go to a futuristic theme park where Dinosaurs are brought back to life via some bioengineering process, the book ends with Billy befriending the Cloneasaurus and eager for the chance to return to the theme park. That is a unique if not very good story that differs substantially from Jurassic Park. So long as Skinner didn't just copy Crichton's Jurassic Park, and then slap on that title he would face no opposition to publication on that front, he would face plenty of opposition for the reason Apu gave, the title's awful and there isn't a market for it.
The reason I made this post is to clarify a misconception about copyright, as bad as it is, it isn't that Draconian, not yet at least. A common post I see on public domain and creative writing message boards is asking for "free to use versions of X" and while the discussion started by these questions can sometimes bring attention to an underrated character or story It's not necessary, just make up your own version. Public Domain and Creative Commons media are tools to be used, but that doesn't mean you're restricted to them, you can make your own superheroes despite DC and Marvel existing, you can animate talking animals without getting the go-ahead from Disney and whoever owns Warner Brothers now.
