How do scientists know that a fossil fragment they found belongs to an already existing dinosaur and not a new species?

Question

Say when a scientist discovers a new skull fragment from a T-Rex, how do they know it’s a skull fragment from a T-Rex and not like a fragment of some unknown species of dinosaur?

In: Biology

Answer 1

Comparison with known parts.

When a new dinosaur is described, they describe the traits that it has and doesn’t have that make it unique. These can then be compared. For example one part of the skull might be curved in one dinosaur, but angular in another.

However, sometimes we just don’t know . *Irritator* was a relative of *Spinosaurus* that lived in South America, and either lived with another spinosaur called *Angaturama* or Angaturama is actually a junior synonym (another name for an already existing species, and so is invalid). There’s no overlap between the known material of the two so we don’t know for sure if they’re the same or not.