Google Books preview of chapter in new book that reviews early synapsids (cut off mid-therapsids, however):
Kenneth D. Angielczyk and Christian f. Kammerer (2018)
Non-Mammalian Synapsids
in Frank Zachos, Robert Asher, editors. Mammalian Evolution, Diversity and Systematics.
Walter de Gruyter GmbH & Co KG,
But see this reaction...