Born in Kansas City, Mo., in 1925, Cross moved to Lawrence in 1951 to teach systematics and ecology at KU. There, he worked primarily with graduate students and was a curator for the Natural History Museum.
Although he retired in 1991, he continued to work at the museum at least once a week as a curator emeritus, teaching students how to identify various species of fish, until his death.
While many biologists examine fish under a microscope to identify the species, Cross would hike up his pants, trudge through a stream and identify them with his naked eye, said Joseph Collins, a former colleague.
"He's the only person I know who could do that," Collins said. "The better students learned from him and went ahead, and the rest of us were left to look under the microscope."
His son, Frank Cross Jr., said his dad traversed the state, wading through even the smallest ponds to examine various species of fish.
"He loved field work," he said. "He traveled all over the state investigating every little creek, even ponds on peoples farms, to see what was there."
Cross literally wrote the book on Kansas fishes. His first textbook, The Handbook of Fishes in Kansas, was published in 1967. He later co-wrote a text called "Fishes in Kansas" with Collins in 1975 and revised it in 1995.
"Almost everybody in the state of Kansas who got a degree in biology learned about fishes from Frank or his writings," Collins said.
Students who got to work with Cross in person were at an advantage, he added. People were drawn to his gentle demeanor and excellent sense of humor, said Ed Wiley, curator at the Natural History Museum.
"He was a realist in terms of his outlook on life and the way he approached life," Wiley said. "I liked him immensely. He was the sort of person who, when he gave his opinion, people listened to it."
Brad Kemp, assistant director for public affairs at the museum, said fair-mindedness and an unassuming nature were Cross' trademark traits.
"What I think of when I think of Frank Cross is an unfailing, compelling sense of fairness and unfailing good will," he said. "He was always very friendly, and even after his retirement he cared deeply about this program and his colleagues."
Although Cross was devoted to his work, family was always most important, said wife Maria Cross and son Frank Cross Jr. He is survived by three children.
"He would want to be remembered for his family and how much we cared for him and he cared for us," said Frank Cross Jr., a law professor at the University of Texas. "I certainly use him as a guide for how to live my life."