Diprotodon went extinct because it was vulnerable and was not built for an outsider. It had 2 predators which after its extinction would be fought over by 2 apex predators humans and megalania. This was australian megafauna collapse. This was a nuke to australia's animal life. With human hunting climate change etc. When diprotodon fell a wire snapped which led to the falling of the megafauna bridge.
Around the same time as t.rex existence of ruler of north america on other parts of the world such as south america had the 2nd largest carnivore to walk on earth, giganotosaurus. If north america and south america collided expect a battle between the giants. However if the asteroid never hit earth and the continents collided together, t.rex and giganotosaurus would have met
Stethacanthus was unique. Its dorsal fin was like an ironing board, as it was flat at the top with hundreds of tooth-shaped scales. Scientists cannot know for sure what this strange fine was used for, but it could have been for courting and mating, or making the shark look like it had another mouth. This method would have scared off predators.
astronomy-to-zoology: “ Genus: Platybelodon …an extinct genus of mammals related to elephants that lived in Miocene Africa, Europe, Asia and North America. Like other gomphotheres Platybelodon sported...
Carcharodontosaurus dominated the middle cretaceous south african landscape. it lived killing the local sauropods and edmontosaurus or duck billed dinosaurs. it ruled the bottom of the african landscape to itself. However it coexisted with one of the most dangerous predators to exist....spinosaurus
Diictodon had it's little teeth to fight of competing males. However diictodon had an advantage over its superior predators, like gorgonopsid. It lived in small communities of holes they live through. If one saw a predator, all would be alerted of it.