Was Spinosaurus the only sailback dinosaur?
No, some other dinosaurs also had sails. One was Irritator, a
relative of Spinosaurus, which had a similar, but smaller, sail.
Another was Hypacrosaurus, which was a quadrupedal herbivore that
had very high spines on its back. One animal commonly referred to
as a dinosaur, Dimetrodon, was not a dinosaur, but it was a
prehistoric reptile with a sail on its back.