Final answer:
The ancestral mammals, or cynodonts, possessed heterodont teeth composed of incisors, canines, premolars, and molars specialized for various dietary needs. As diphyodonts, these early mammals had two sets of teeth throughout their lifetime, which facilitated a more advanced chewing mechanism and efficient digestion, linked to their endothermic nature.
Step-by-step explanation:
The ancestral mammals, known specifically as cynodonts which first appeared in the Late Permian period roughly 260 million years ago, had a distinct pattern of teeth which indicates their link to modern mammals. An important feature of early mammalian teeth is that they were heterodont, meaning that they had different types and shapes of teeth - incisors, canines, premolars, and molars, specialized for a variety of functions like cutting, tearing, crushing, and grinding different kinds of foods. Additionally, most mammals including their ancestors are considered diphyodonts, which implies that they had two sets of teeth over their lifetime: 'baby' teeth and permanent teeth. The presence of different kinds of teeth was essential for more advanced chewing mechanisms, which, in turn, was crucial for the more efficient digestion necessary to support a higher metabolic rate associated with endothermy, a characteristic of mammals. Changes to the skeletal structure like the presence of a secondary palate and the zygomatic arch, and the development of powerful jaw muscles like the temporalis and the masseter further enabled refined chewing capabilities.