Therapsids have become one of my favourite animal groups recently as I learned more about their history, I have always liked mammals, particularly cetaceans, but I am more interested in therapsids (and other synapsids) as whole group today as I was before. I also like arthropods. Maniraptoran dinosaurs are also among my favourites.
Only just saw this comment, sorry. (You weren't directly replying to me, so it didn't show up in my messages.) Castorocauda has always been a non-mammalian synapsid. It's a docodont, which is close but not in Mammalia proper: [link]