year as Hadrosaurus foulkii, giving a slightly better picture of the form of a hadrosaur. Leidy provided additional description in a 1865 paper. Among his 1858 work Leidy briefly suggested that the animal was likely amphibious in nature; this school of thought about hadrosaurs would come to be dominant for over a century to come. Further discoveries such as "Hadrosaurus minor" and "Ornithotarsus immanis" would come from the East, and Edward Drinker Cope led an expedition to the Judith River Formation where Trachodon was found. Upon the fragments discovered he named seven new species in two genera, as well as assigning material to Hadrosaurus. Cope had studied the jaws of hadrosaurs and come to the conclusion that the teeth were fragile and could have been dislodged incredibly easily. As such, he supposed the animals must have fed largely on soft water plants; he presented this idea to the Philadelphia Academy in 1883, and this idea would come to be very influential on future study. Research would continue in the Judith River area for years to come, but the formation never yielded much more than fragmentary remains, and Cope's species as well as Trachodon itself would be in time be seen as of doubtful validity. The Eastern states, too, would never yield particularly informative specimens. Instead, other sites in the American West would come to provide many very complete specimens that would form the backbone of hadrosaur research. One such specimen was the very complete AMNH 5060 ( belonging to Edmontosaurus annectens), recovered in 1908 by the fossil collector Charles Hazelius Sternberg and his three sons in Converse County, Wyoming. It was described by Henry Osborn in 1912, who dubbed it the "Dinosaur mummy". This specimen's skin was almost completely preserved in the form of impressions. The skin around its hands, thought to represent webbing, was seen as further bolstering the idea that hadrosaurs were very aquatic animals. Cope had planned to write a monograph about the group Ornithopoda, but never made much progress towards it before his death. This unrealized endeavor would come to be the inspiration for Richard Swann Lull and Nelda Wright to work on a similar project decades later. Eventually they realized the whole of Ornithopoda was too broad of a scope, until eventually it was narrowed down to specifically North American hadrosaurs. Their monograph, Hadrosaurian Dinosaurs of North America, was published in 1942, and looked back