What is their main threat for spinosaurus?

Answer 1

For young Spinosaurus, any larger carnivore would have been a major threat.

As an adult, Spinosaurus was designed to eat fish, but lived alongside Carcharodontosaurus, Bahariasaurus, and Stomatosuchus, all of which hunted large dinosaurian prey. Carcharodontosaurus was a powerfully built theropod, or bipedal meat eating dinosaur, and they grew to be 43 feet long with a weight of between 6 and 15 metric tons. Bahariasaurus was also a huge theropod, possibly a ceratosaur, and its size rivaled that of Tyrannosaurus rex and Carcharodontosaurus. Stomatosuchus was a 33 foot long crocodile. In modern times, large carnivores generally don't get along with other large carnivores very well, so it stands to reason that Carcharodontosaurus, Bahariasaurus, and Stomatosuchus were threats to Spinosaurus, especially considering their more powerful jaws and larger teeth. Spinosaurus may have threatened each other, too.