I got this idea for this question from another unrelated thread.
Suppose the meteor that wiped out the dinosaurs 65 million years ago never happened, and the dinosaurs were still among us, what kind of world would it be?
Would we be where we are now technologically? Would we have wiped them out in other ways?
Would they have wiped us out, or would we still be hiding in caves?
How different do you think the world would be today if these creatures were still around?
Gus
The only way we were able to evolve to be more than rodents of unusual size was the death of the top level predators. The best way I can think of to where humans and dinos could live together is have a populace of dinosaurs on one continent separated from the mammals they left behind. For example, say they were alive and well on the N. and S. Americas, but extinct in Asia and Europe.
I’m sure our ancestors would have tried to kill them all off as soon as they could, much like the wolves in Europe.
I think predators that size in the Americas might have kept hunter-gatherers out.
Our mamalian ancestors took over the world after the dinosaurs were wiped out. They needed the ecological freedom to do so, just like the dinosaurs profited from the mass extinction at the end of the Permian, 245 million years ago. Though, to be a bit more precise, the dinosaurs became dominant only at the end of the Triassic when they replaced many of the vanishing amphibians, reptiles and mammal-like reptiles that had existed earlier.
How the world would look like from the outside if the dinosaurs hadn’t been wiped out, is easy enough to say: pretty much the way it does today, because plate tectonics would have moved the continents around the same way - which also means that many of the fundamental climate factors would have worked similarly with or without the dinosaurs. 
But the composition of life on our planet would be different, for sure. And life has an enormous impact on the state of affairs on a planet, even on things like the composition of the atmosphere and the chemistry of the oceans (which, in return, influence the climate).
So, how would life look today? No idea. You see, life, species interact; they develop as much in competition as in cooperation – and both factors stabilize and change the status quo, just like the fundamental forces of evolution: selection and mutation.
We cannot say how the dinosaurs would have further developed and if they could have stayed as dominant in a colder climate, for instance, that was to come. Maybe mammalians would have seized the chance and maybe more dinosaur species would have become more mammalian-like. Maybe one species would have learned to see the benefits of controlled fire.
Without massive extinction events, the composition of life surely wouldn’t have been altered as radically as it happened on more than one occassion but it would have adapted to the longterm changes that are inevitable on a planet with a hot core, plate tectonics, oceans and an atmosphere. And dependant on a life-giver that behaves reliably but not totally stable.
Life would be different, very different, but it still would be. And might even know that it is.
Another event later would have got them.
It would be just like in this book!
They would have grown feathers and learned to live in trees.
Since no factual answer is possible, let’s move this to IMHO from GQ.
samclem Moderator
Well, first off it is extremely unlikely that we would be here at all. Towards the end of the cretaceous period, we know that there were some pretty interesting animals evolving. Some of the smaller theropods like the raptor family had evolved insulating feathers. They also had grasping hands, a bipedal stance, stereoscopic vision, The ability to make complex vocalizations, a social structure, and an increasing brain/ body ratio. It isn’t unreasonable to think that such an animal might well have evolved into a sapient being. The million dollar question though, is given their significant adaptations to their predatory diet, would they evolve advanced tool use. Humans as omnivores needed to evolve the brain capacity for abstract thought and advanced tool use to level the playing field. The likely candidates in the cretaceous were already efficient and successful predators. Supposing they did though, I’m not certain that they would eventually produce as advanced technology as we have. I can easily see them becoming a herding/ pastoral society, but having less need for technological crutches, I’m not at all certain they would generate high tech.
Harry Harrison’s Eden trilogy (beginning with West of Eden) is based on this very premise (though it’s the mammals occupying the Americas and the dinos elsewhere). It’s been many years since I’ve read it, but I recall it being a fascinating read, with well-developed reptilian culture and technology (which is organic rather than mechanical). The humans in the story are primitive in comparison, reaching somewhere around what we would call Stone Age technology.
Kind of like Dinotopia
I was going to being up West of Eden as well but beaten to it. Dougal Dixon also wrote a book called The New Dinosaurs that speculates on what Dinos would look like after an extra 65 million years of evolution. It only touches on sentience in the appendices though.
For what it is worth, a case could be made that technically there is a real life answer to this question and that answer is birds. You can say that birds are dinosaurs’ direct decedents.
Well, the bird offshoot would still be successful, and I think dinosaurs would have evolved away from the huge species - they wouldn’t thrive in our thinner atmosphere today. And many species would have been hunted to extinction if humans had evolved again.
George Washington would have overlooked Yorktown on the back of a Triceratops (I know they didn’t exist but that would have looked nifty for the cover).
Hey Mr. Turtledove, that’s my idea. You stay away.
The idea of a Saurus Erectus is really interesting.
It annoys me to end end how badly headline writers do. From Cardinal’s first cite, the headline is “Triceratops ‘Never Existed’”. But read the article and you find Torosaurus and triceratops will now likely be reclassified as a single species—but don’t shed a tear just yet: The name “triceratops” will be the one that stays, the scientists say.The exact opposite of what the headline says. :smack:
Oh, yeah, I knew that news - but I knew it as Torosaurus is one sex of a mature triceratops.
turns out they aren’t real
Christian group to schools: Stop filling kids’ heads with dinosaurs
i think they plan a fight with the dino riders.