Claims are a very common topic, and claims needs to be verified through sources and evidence.
Whenever you make a claim in an article you have the responsibility to provide a source to your claim through references, otherwise your claim might get questioned or it will be removed.
Articles with uncertain claims will be marked with "[uncertain claim - verification needed]" after the end of the sentence.
Example: "The mosasaur is a dinosaur.[uncertain claim - verification needed]"