supports the monophyly of cephalopods, does not bear on the Palcephalopod/Neocephalopod question, since the only cephalopods included were Nautilus and coleoids. Recent revisions For an in-process revision of Treatise Part K, King & Evans (2019) reclassified nautiloids sensu lato into five subclasses. Major groups were primarily defined by variation in their muscle attachment types. Other traits referenced during this reclassification include protoconch morphology, connecting ring structure, and the extent of cameral and endosiphuncular deposits. While most previous studies referred to subclasses with the suffix '-oidea', these authors instead opted for the suffix '-ia', to prevent confusion between group levels. For example, Nautiloidea sensu stricto was renamed to Nautilia, to differentiate it from the informal broader definition of "nautiloid". In addition, they used the unsimplified names for orders, with the suffix '-atida' rather than the common simplified form, '-ida'. Subclass †Plectronoceratia (formerly Plectronoceratoidea) Order †Plectronoceratida Order †Yanheceratida Order †Protactinoceratida Subclass †Multiceratia (formerly Multiceratoidea) Order †Ellesmeroceratida Order †Cyrtocerinida Order †Bisonoceratida Order †Oncoceratida Order †Discosorida Subclass †Tarphyceratia Order †Tarphyceratida Order †Ascoceratida Subclass Nautilia (formerly Nautiloidea sensu stricto) Order Nautilida Subclass †Orthoceratia (formerly Orthoceratoidea) Order †Rioceratida Order †Dissidoceratida Order †Orthoceratida Order †Pseudorthoceratida Order †Actinoceratida Order †Astroviida (suborders †Lituitina and †Pallioceratina) Order †Endoceratida Traditional nautiloid classification schemes emphasize certain character traits over others, potentially involving personal bias as to which traits are worth emphasizing according to different authors. This issue may be resolved by sampling all morphological traits equally through bayesian phylogenetic inference. The first cephalopod-focused paper to use this technique was published by Pohle et al. (2022). They recovered several previously hypothesized groups, though many orders were determined to be paraphyletic. The study was focused on early cephalopod diversification in the Late Cambrian and Ordovician, and did not discuss in detail the origin of post-Ordovician groups. The following is a simplified version of their cladogram, showing early cephalopod relationships to the order level (although various isolated families also originated during this diversification event): Gallery See also Ammonoidea Belemnoidea Lituites References Further reading http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php (retrieved on May 11, 2014) External links Nautiloids: The First Cephalopods (TONMO.com) Palaeos Mollusc subclasses Paleozoic cephalopods Mesozoic cephalopods Cenozoic cephalopods Transitional fossils Furongian first appearances Extant Cambrian first appearances Paraphyletic groups