Transitions in the evolution of synapsid tails

Mammals are unique among land vertebrates in a number of respects, from their locomotory posture to their ecomorphological diversity. The evolutionary assembly of unique traits began following the evolution of the amniotes, which occurred in the upper Carboniferous. One lineage of the amniotes, referred to as Synapsida, is today defined as Mammalia plus its stem-lineage, and originates by 305 Ma, when their earliest fossils occur (potentially earlier at 315 Ma, but this is conditional on the validity of Protoclepsydrops as a definitive member of Synapsida).