The "proto" in this case would have to refer to a synapsid, which have been described as "mammal-like reptiles", some of whom were the ancestors of the mammals

The "proto" in this case would have to refer to a synapsid, which have been described as "mammal-like reptiles", some of whom were the ancestors of the mammals which didn't yet exist 295 million years ago. https://en.m.wikipedia.org/wiki/Synapsida https://en.m.wikipedia.org/wiki/Synapsida