I WONDER - When Was The Ankylosaurus First Discovered?

The video discusses the discovery of Ankylosaurus fossils in the Hell Creek Formation in Montana, USA, by Barnum Brown in 1906. Brown named the species Ankylosaurus Magnaventris in 1908, describing it as a 'diffuse lizard with a great belly.' Despite numerous fossil discoveries in the USA and Canada, a complete Ankylosaurus fossil has not been found. The Ankylosaurus lived in North America during the late Cretaceous period and was among the last dinosaurs before extinction.

In what year did Barnum Brown describe the Ankylosaurus?

What is notable about the completeness of Ankylosaurus fossils found to date?