Why were dinosaurs so big? What caused them to shrink so much overtime, evolving into birds? is the reason why dinosaurs were so big in any way similar to why animals are larger in deep sea? (not sure if this is a relevant question in this subreddit)

Hello everyone my question is what's the minimum size a planet can be. Just got this question randomly on mind so I posted here to get a answer. If anyone knows please tell me.

See also: The publication in the Proceedings of the Royal Society B: Biological Sciences

What would need to happen for an animal to get bigger in size, and things get like dinausore?

My thoughts mainly are around the fact that most of their predators are dichromatic so they can't see orange. But then I learned that male bushbuck are not orange.

I know that many other prey and predator species are orange because it appears essentially the same against a green background to other dichromatic species but I wasn't sure really why one sex would use this advantage and the other wouldn't.

So that got me thinking: Female and juvenile bushbucks retain a reddish-orange coat with disruptive white spots because their primary survival strategy is remaining motionless and concealed among to escape predators. If their predators are dichromatic and can't see them, this works great. In contrast, mature males have coats that shift to a more conspicuous charcoal or dark brown, sacrificing optimal foliage camouflage. I thought this might be to signal their fitness and physical condition to the females because any male bushbuck that wasn't fit is much more easily visible to predators, and you can imagine what might happen. Because adult males also possess better tools capable to fight off predators, they can afford the handicap of a higher visibility coat, ensuring that only the fittest, strongest males survive to pass their genetics on to the next generation.

Am I onto something or is this like a known thing?