Marcus Ward Lyon Jr. (February 5, 1875 – May 19, 1942) was an American mammalogist, bacteriologist, and pathologist. He was born into a military family, and demonstrated an early interest in zoology by collecting local wildlife around his father's army posts. He graduated from Brown University in 1897, and continued his studies at George Washington University while working part-time at the United States National Museum (USNM). At the same time, he taught at Howard University Medical School and later George Washington University Medical School. He received his Ph.D. from George Washington University in 1913. In 1919, he and his wife, Martha, moved to South Bend, Indiana to join a newly opened clinic. Prior to moving, Lyon had published many papers on mammalogy, both during and after his ten