mammaliaformen

Mammaliaformes is a clade within Synapsida that includes the crown group Mammalia (the living mammals) and several extinct stem-mammals that lie closer to mammals than to other cynodonts. In cladistic terms, it is defined as the most recent common ancestor of Mammalia and Docodonta and all of its descendants. As such, it sits just outside the crown group in many classifications, but within the broader mammal lineage.

Over time the composition of Mammaliaformes has varied with new fossil finds. Traditionally it included groups such as Morganucodontidae and Docodonta. The placement of Haramiyida is debated: some analyses place Haramiyida within Mammaliaformes, others treat them as more distant cynodonts.

Typical mammaliaforms show trends toward mammalian traits, including differentiated dentition and a shift in jaw mechanics compared with earlier cynodonts. Many retained some reptilian features such as a dental arrangement and jaw joints, but over time the mammaliaform lineage shows increasing specialization of the jaw and early signs of the mammalian middle ear. They were generally small and likely had diverse diets, with ecological roles ranging from insectivory to omnivory. The study of mammaliaformes provides key insights into the early evolution of mammals and the transition from cynodonts to crown Mammalia.