He has worked with dinosaur remains from the southwest United States of America and Mexico [1][2][3] and has been responsible for discovering new and important genera.
[15] At the same site where he found Gastonia and Utahraptor, Kirkland has also excavated fossils of the therizinosaur Falcarius.
An expert on the Mesozoic, he has spent more than thirty years excavating fossils across the southwestern US and Mexico authoring and coauthoring more than 75 professional papers.
The reconstruction of ancient marine and terrestrial environments, biostratigraphy, paleoecology, and mass extinctions are some of his interests.
His researches in the middle Cretaceous of Utah indicate that the origins of Alaska and the first great Asian-North American faunal interchange occurred about 100 million years ago, which his numerous trips to China and Mongolia have substantiated.