Hylonomus

Hylonomus (; from Greek hylos, meaning 'forest', and nomo, meaning 'dweller') is an extinct genus of early possible amniote that lived 318 million years ago during the Bashkirian stage of the Late Carboniferous. The genus contains a single species, Hylonomus lyelli. Hylonomus lyelli was named the Provincial Fossil of Nova Scotia in 2002. It was originally interpreted as a 'microsaur' or ancestral to crown group amniotes. Although a number of early 21st century cladistic analyses have suggested that Hylonomus is the earliest known reptile, a 2025 analysis placed Hylonomus outside of crown group Amniota, which would make it less closely related to modern reptiles than mammals are.