Collection: Mazon Creek Tully Monsters

Tullimonstrum gregarium, popularly known as The Tully Monster, came to the attention of researchers when, in 1955, amateur collector Francis Tully presented his unusual find to curators at Chicago’s Field Museum of Natural History. The creature was bizarre, owing to an elongate tapering body with a squid-like tail, an extended snout sporting a toothy claw at its end, and what appeared to be a pair of stalked eyes projecting perpendicular to its body. It lived during the middle-Pennsylvanian Period, roughly 307 million years ago, in a marine environment adjacent to the tropical swamps of northeastern Illinois. In 1966, this strange animal was given a scientific name to honor its peculiar form and its discoverer. Found in ironstone concretions from the famous Mazon Creek Lagerstätte (or Mother Lode) and made accessible to collectors through industrial coal mining, this soft-bodied “monster” eluded formal classification for over 60 years. Not until 2016, by extensive morphological research from Yale University and other institutions, was the Tully Monster determined to be an early vertebrate and likely a jawless fish on the stem lineage of modern-day lampreys. It was in 1989 that it became the State Fossil of Illinois.