User:Snoteleks/Arthropoda

Phylogeny of stem-group arthropods
Modern interpretations of the basal extinct stem-group of Arthropoda separate it into the following groups, from most basal to most crownward : The Deuteropoda is a recently established clade uniting the crown-group (living) arthropods with these "upper stem-group" fossils of more uncertain positions. The clade is defined by important changes to the structure of the head region such as the appearance of a differentiated first appendage pair (the deutocerebral pair). However, recent analyses show that these "upper stem-groups" might be inside the crown-group: Megacheira have been recovered as more closely related to Chelicerates, some bivalved forms such as Hymenocarina are consistently shown to be mandibulates , and similarly Fuxianhuiida might also be mandibulates. The following cladogram shows the probable relationships between crown-group Arthropoda and stem-group Arthropoda as of 2022, including two new fossils found to be the most early branches of Deuteropoda  (living groups are marked in bold):
 * The "Giant" or "Siberiid Lobopodians", such as Jianshanopodia, Siberion and Megadictyon, are the most basal grade in the total-group Arthropoda.
 * The "Gilled Lobopodians", such as Kerygmachela, Pambdelurion and Opabinia, are the second most basal grade.
 * The anomalocarids or Radiodonta come in third position, and are thought to be monophyletic.
 * The Isoxyids have an established position as closer to the crown-group than anomalocarids and, according to more recent stuidies, are inside the crown-group itself.
 * An "upper stem-group" assemblage of three fossil groups of more uncertain position but contained within Deuteropoda : the Fuxianhuiida, the Megacheira and a group of bivalved arthropods known as Hymenocarina.

Note that the subphylum Artiopoda, containing the trilobites, is closer to mandibulates than to chelicerates in the cladogram above, but older analyses place them as the sister group of chelicerates united under the clade Arachnomorpha.

Phylogeny of living arthropods
The following cladogram shows the internal relationships between all the living classes of arthropods as of 2022 :