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.
~260 MYA Cynodonts
More mammal-like jaw and teeth. Started when therapsids developed a stronger mammal-threshold package: more mammal-like jaws and teeth, plus features like a secondary palate, which helped separate breathing from chewing. I’d use “mammal-like jaw and teeth” as the public-facing marker.
Last Non-Mammaliaform Cynodonts
Tritylodontids were not mammals, but they were late-surviving mammal-side cousins that carried many mammal-like traits without crossing into the mammaliaform line.
Last Non-Mammaliaform Cynodonts Read More »
First Cynodonts
Cynodonts were a more advanced branch of therapsids where the mammal-like jaw, teeth, palate, and breathing package began to come together.
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.