Derek Main, the energetic director of a north Arlington fossil dig who led legions on hunts for prehistoric creatures, died Tuesday, less than a month after graduating with his doctorate from the University of Texas at Arlington. He was 41.Mr. Main's body was found in his Dallas apartment. The Dallas County medical examiner's office said a ruling on the cause of his death is pending.Mr. Main, who was a graduate student and lecturer at UT Arlington, led his students and other enthusiasts on many "dino digs" at the so-called Arlington Archosaur Site, located on part of 2,000 acres that is home to the Viridian housing development."Derek was passionate about science. He lived it every day. That's why I felt that he would be a good Ph.D. candidate," said Chris Scotese, an earth and environmental science professor who retired from UTA in 2011. Scotese advised Mr. Main on his doctoral dissertation. Since 2008, excavations at the Arlington site have turned up rare fossils of prehistoric turtles, sharks, crocodiles and duck-billed dinosaurs. Several were entirely new species — including a 23-foot-long crocodile, a turtle and a lungfish — that lived about 95 million years ago in the Cretaceous period, in the age of dinosaurs.Under Mr. Main's watch, the Arlington Archosaur Site — archosaur means ruling reptile — was much less restrictive to the public than many other dig sites of that caliber, said Art Sahlstein, who is caretaker and one of the discoverers of the site. "Derek will be remembered as an educator who loved paleontology and shared it with the people of Texas," Sahlstein said. "He was hungry and enthusiastic. His studies have opened a new light on that period of time – 95 to 98 million years ago – which was a poorly understood period."Bradley Carter, a jewelry store manager who discovered the new lungfish species, said he was just a fossil-hunting hobbyist until Mr. Main showed him how his work could have scientific value. "If I had had somebody as passionate as him to look up to when I was a child, I probably would have continued my education further than I have, and pursued my passion like he did," said Carter, 28.The Archosaur site's Facebook page was flooded with condolences for Mr. Main.Anissa Camp wrote, "I don't have words that can adequately describe the depth of loss I feel with the death of Dr. Derek Main. I am just grateful to have known Derek."Born Aug. 8, 1971 in Irving, he was the son of Norman A. Main Jr. and Jannie Davis Main. He graduated from MacArthur High School in Irving. He received his bachelor's degree from UT Dallas and his master of science in geology from UTA in 2005, according to the Shorthorn, the UTA campus newspaper.Mr. Main taught earth history, dinosaurs and earth systems at UTA. He also taught courses at Northlake College and Tarrant County College, the newspaper reported.Scotese described how his friend wanted to be a professional paleontologist with goals of teaching on the university level and becoming a museum curator."Derek was a people person. He really got everyone interested in science," Scotese said. "He got people out in the hot sun digging in the dirt, but he also made them feel important.""Derek's site"Carter said it's too soon to know how the void left by Mr. Main's death will be filled. But he expects no changes in the dig site operation."Right now we're in a state of shock," he said. "Our intentions are to keep the site going, for him. That will always be Derek's site." Survivors include his mother; a brother, Darren Main of Fort Worth; fiancee, Deborah Nixon of Dallas; and several cousins.