>>40003015And you are willing to leave out one temporal fenestra on each side of the skull, differentiated teeth, endothermy, among others.
So, follow me here. These animals have one temporal fenestra, and differentiated teeth. The only living animals with both of those qualities are mammals. It is obvious it cannot be a diapsid (all reptiles and birds), so it can only be more related to mammals than birds and reptiles.
Now, it is true that:
>We have no idea whether they had fur>They lived far before the first definite mammals>We have no idea whether they could lactate>Their features look, for the most part, closer to ancestral reptiles than usSo they are probably not mammals. They were similar to reptiles, yet had a few but meaningful things that were definitely mammal features. Hence the name "mammal-like reptiles" or "stem-mammals".
