In museum collections, a fossil can remain overlooked, hidden in a drawer and undervalued. One such fossil at the Field Museum in Chicago was once thought to belong to a known species, but it actually housed an ancestor of amphibians that had never been described before, dating back several hundred million years. According to research published on September 24, 2026, in the Journal of Vertebrate Paleontology, two students identified a 309-million-year-old creature previously classified under a neighboring species. These small Carboniferous vertebrates look so similar that museum collections often group them into a single, general category. The newly discovered amphibian ancestor, named Jeanerpeton mazonensis, already displays traits seen in modern frogs and salamanders. The fossil was originally collected by an amateur and later donated to the museum, where it remained in storage for years without drawing attention. Museum curators initially classified it as Amphibamus grandiceps, a well-known regional species. According to postdoctoral researcher Calvin So, this name was used as a general category for fossils that looked too similar to each other, which long obscured the true diversity of the collection. Through careful re-examination, students Payton Kohlberg and Allison Sefcovic, guided by curator Arjan Mann, were able to distinguish this unique creature from the others. The creature lived 309 million years ago during the Carboniferous period, in a marshy delta that now lies beneath Chicago. At that time, giant insects and the first four-legged vertebrates thrived in the waterlogged forests. The discovery was made possible by the exceptional preservation of the Mazon Creek site. The rapid deposition of delta sediments trapped the bodies of animals before they could decay, encasing them in stone nodules similar to how crinoids form. This process has made Mazon Creek one of the richest sources of Carboniferous life, where early land animals, giant insects, and aquatic creatures coexisted. The fossil has retained many details that are usually lost during fossilization. Researchers can see scales on the back, fine ventral ribs known as gastralia, the imprint of the eyes, and even the pads under the fingers. The creature appears squat, with the body structure of a salamander but the build of a frog. These features indicate that Jeanerpeton is a close relative of the direct ancestors of today's frogs and salamanders. By rediscovering this creature, researchers have pushed back the origin of the physical traits seen in modern amphibians to 309 million years ago. However, caution is needed, as a single specimen is not enough to fully determine all evolutionary relationships. The name Jeanerpeton carries a personal tribute, as the two young researchers named it after their mothers, both named Jean, making it "crawling Jean" from Mazon Creek. Other fossils previously classified under the same name may still be hiding in the collections, and the team now plans to re-examine them one by one to determine how many additional species may be waiting to be discovered.