Hesperornithoides

Hesperornithoides is a troodontid theropod dinosaur from the Upper Jurassic Morrison Formation of western North America. 
Discovery.
The fossil was found in Wyoming, as the site was carefully documented by the collectors.
Classification.
A phylogenetic analysis was presented in an abstract in the "Journal of Vertebrate Paleontology" in 2005. The analysis decided the specimen was a close relative of "Sinornithoides".
Significance.
This dinosaur is very significant because it is the oldest known troodontid from North America. Until the discovery of Lori, troodontids were believed to have first originated and evolved in Asia and then migrated to North America. Most troodontids were discovered in Asia, and the previously oldest known troodontids, from the Lower Cretaceous, lived there.