Abstract

James A. (“Dinosaur Jim”) Jensen’s paleontological career was a dynamic chapter in Utah’s vertebrate paleontologic history in the 1960s through the 1970s. Much of his success stemmed from the local contacts he made with people familiar with the Utah backcountry, and his charismatic public persona. As a result, he built one of the more active paleontological field programs in the country for his time, collecting major fossil troves from central Utah, including the “world’s smallest dinosaur” and the first relatively complete dinosaur egg in North America.

This is a historical summary of Jim Jensen’s fossil discoveries in central Utah presented to illustrate the paleontological diversity of the region. The importance of some of these finds, especially from the Triassic Chinle Formation, has yet to be fully realized. Discoveries in the Upper Jurassic Morrison and Lower Cretaceous Cedar Mountain Formations provided the first look at some important aspects of known dinosaurs. His work in the North Horn Formation aided students of mammals and lower vertebrates and helped preserve the dinosaur record of the Late Cretaceous. His investigation of the Paleocene Flagstaff Formation and Eocene Green River Formation resulted in the recovery of exceptionally preserved champsosaurs, fish, and trace fossils. And, even though Pleistocene fossils were not his forte, he cultivated relationships with others who routinely reported Ice Age fossils to him, resulting in the recovery of spectacular specimens. As scientifically valuable as these findings are, each discovery also had a human side, including both problems and successes, some of which are just coming to light.