Re: [dinosaur] Diadectomorphs and seymouriamorphs as amniotes from inner ear morphology

> Disagree. The standard usage of "stem-" in invertebrate paleo refers to members outside the crown group but closer to it than to the next closest crown group (so stem-arthropod, stem-mollusk, etc.). But "non-crown amniotes" is (as noted) a nonsensical term.

But "members of a taxon, but not of its crown-group" is exactly what "stem-group" has meant ever since Hennig. I don't think I've seen phylogenetic definitions for Arthropoda or Mollusca, and Arthropoda at least is usually treated as having an apomorphy-based definition (it's not clear if even the trilobites are crown-group arthropods, but they're not going to be kicked out of Arthropoda!), so there are non-crown arthropods = stem-arthropods.