Because of its notorious fight against a Tyrannosaurus rex in back in JP III, it seems that pretty much every time a Spino shows up somewhere in media, it is required to have a confrontation with a T. rex.

Yes, I know, this is pretty much the most controversial dinosaur topic ever. Please don't get into a huge argument in the comments. Anyways, I'm gonna get started with defending the seemingly less popular side of this whole discussion. Also keep in mind I will mainly be talking about the dinosaurs abilities on land. This will be written assuming the reader knows quite a bit about both animals.

For the longest time I was certain that Rex was the obvious victor in this fight. When the Spino's aquatic adaptations were discovered, it seemed to solidify the creature's inferiority to the Rex. How could this mutant duck tadpole take on a near-perfect hunter? Recently, however, I've realized I have been looking at this the wrong way. Let me explain.

The Tyrannosaurus was the perfect killer. Killer. Its most highly specialized feature - the incredibly powerful jaws - were built to deliver a quick, bone-crunching death. It was probably the only land predator ever that could stand a chance against an Ankylosaurus or Triceratops. And yes, that includes Spinosaurus. So why am I still saying the Spino would win?

Hunting is much different than a fight over food or territory between predators. Most of the time, fights between large carnivores do not end with (immediate) death, and rather end when one side gives up and retreats. The Rex was not well equipped or experienced in dealing with other carnivores near its size. In fact, it was the only large carnivore in its time + habitat. Fights between members of the species would probably be awkward, and mainly consist of the Tyrannosaurus body slamming with their barrel chests. This would undoubtedly do plenty of damage with how much the creature weighed, but much less than a bite from those massive jaws could do.

Spinosaurus, on the other hand, had two weapons and 4 major advantages when it came to fighting other large theropods. It had huge claws that could clearly do serious damage, and a bite that is far less than a Tyrannosaurus' but much stronger than most give it credit for. Then there are the advantages:

1. Intimidation: Especially when rearing up by using its tail as a counterbalance, which it most likely could do, the Spinosaurus would seem gigantic to any opponent.

2. Reach: The Spino will get the first strike more often than not.

3. Experience: Charcarodontosaurus and Bahariasaurus were both large carnivores who shared a habitat with Spinosaurus. The Spino had to have been well equipped to deal with these giants.

4. Center of gravity: A seemingly small detail that would actually help out a ton in a fight against a body-slamming Rex.

The only advantages the Rex has are bulkiness and intelligence. Its bite, which is its most powerful weapon, is almost useless in an actual territorial dispute.

Fight Time (All on land)

Most Likely Scenario: They see each other, but do not engage as the Rex seems like a jacked-up Charcar that a Spino doesn't want to mess with, and the Spino is the first carnivore that a Rex has ever seen that looks substantially bigger than itself. Remember, these are animals, not movie monsters who want to rip each other's throats out no matter what. These things feel fear/are instinctively wary of each other and know a confrontation could lead to serious injury.

Less Likely (But more interesting) Scenario: The creatures challenge each other for whatever reason. They keep their distance for a while, knowing that one serious injury could spell death later on. The Rex comes within striking distance eventually, and the Spino whacks or bites it on the face a couple times, drawing blood. Head injuries will bleed profusely. This is enough to scare the Rex into leaving the battle. Though the Spino is victorious, the Rex will probably survive the injuries and live to tell the tale of the Tadpole Monster to its grandkids or something.

Deathmatch: If the two animals were intent on killing each other and didn't care about any injuries they sustained, the Rex is more than likely going to win. I don't think I have to explain this one.

Spino's Realistic Victory Chance on Land: 75-85%

Spino's Deathmatch Victory Chance on Land: 10-20%

Spino's Realistic Victory Chance in Water cuz why not: 95%

Spino's Deathmatch Victory Chance in Water: 60-70%

Anyways, this was all just my opinion. Feel free to agree or disagree. In the end, both of these are amazing animals that I'm always hoping to learn more about. Thanks for reading!

EDIT: I'm going to stop responding to comments as there are way too many for me to respond to them all, but thanks for your thoughts and the attention!

Last image from Goji Center.