First Therapsids
Therapsids mark the point where the mammal-side branch became more active, more specialized, and more clearly aimed toward the later mammal body plan.
~275 MYA Therapsids
More upright limb posture. Started when synapsids became more mammal-like in body plan, especially with a more upright posture and more differentiated teeth. Britannica also notes their single temporal opening, mammal-like incisors, canines, cheek teeth, and modified limbs.
Last Non-Cynodont Therapsids
Dicynodonts were late-surviving non-cynodont therapsids: mammal-side animals, but not on the direct road to mammals.
Last Non-Cynodont Therapsids Read More »
First Synapsids
Early synapsids looked reptile-like, but they were not on the reptile line. They were the first recognizable step on the long road toward mammals.