I don't always draw dinosaurs... But when I do, I draw MEGAPREDATORS. Despite Spinosaurus being the largest land predator discovered they may not have been the strongest, so I imagine their bodies were designed to make them appear even larger to intimidate other predators. Also to find mates I'm sure. That's my professional opinion, from professor Devon.
Actually I love dinosaurs. All of'em. Spinosaurus isn't even in my top 10 (I did it as a request), but she'll definitely do. It has inspired me to draw others.