Mammals, the dominant group of warm-blooded vertebrates on Earth today, have a deep evolutionary history that stretches back over 300 million years. Their origins can be traced to the synapsids, a group of amniotes that first appeared in the late Carboniferous period. These early synapsids were distinct from reptiles and birds, possessing a single temporal fenestra, an opening in the skull that allowed for stronger jaw muscles. Over millions of years, synapsids diversified into a variety of forms, some of which gave rise to the therapsids, the direct ancestors of modern mammals.

During the Permian period, therapsids became the dominant terrestrial vertebrates, developing more advanced characteristics such as differentiated teeth, a more upright posture, and improved metabolic efficiency. However, the Permian-Triassic extinction event, the most severe mass extinction in Earth's history, led to a significant decline in their diversity. Those that survived continued to evolve, giving rise to cynodonts, a subgroup of therapsids that displayed increasingly mammal-like features. Cynodonts had more complex teeth, enhanced jaw mechanics, and possibly even fur, adaptations that would later define true mammals.