Which traits did therapsids have that resembled those of mammals?

Although therapsids are historically referred to as "mammal-like reptiles," it is inaccurate to classify them as reptiles; they are a distinct clade of synapsids that served as the evolutionary stock from which mammals emerged.12

Therapsids exhibited several key traits that resemble those found in mammals:

• Dentition: Most species possessed differentiated teeth, including nipping incisors, large stabbing canines, and grinding cheek teeth, a condition known as heterodonty.12
• Skull Structure: Like mammals, the therapsid skull featured a single opening in the temporal region, bounded by a bony arch.1
• Palate: Advanced forms developed a secondary palate, which separates the food and air passages, allowing for breathing while eating.12
• Locomotion: They modified their limbs and limb girdles for four-footed locomotion, eventually bringing the limbs closer to the trunk to improve movement mechanics.12
• Musculature: The temporal musculature, responsible for closing the jaw, was expanded in advanced forms.2

While these features show a clear evolutionary trajectory toward the mammalian condition, therapsids retained primitive traits, such as a lower jaw composed of multiple bones rather than the single dentary bone found in mammals.1