Last Non-Therapsid Synapsids
Late caseids represent the fading old-line synapsids: still mammal-side animals, but not yet therapsids.
Last Non-Therapsid Synapsids Read More »
~320 MYA Synapsids
One temporal opening behind each eye. Started when early amniotes evolved a skull with one temporal opening behind each eye. That opening marks the mammal-side branch apart from the reptile/bird side.
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.