Neoplesiosauria

Relationships

Another way to define a clade is to let it consist of all species more closely related to a certain species that one in any case wishes to include in the clade than to another species that one to the contrary desires to exclude. Such a clade is called a "stem clade". Such a definition has the advantage that it is easier to include all species with a certain morphology. Plesiosauria was in 2010 by Hillary Ketchum and Roger Benson defined as such a stem-based taxon: "all taxa more closely related to Plesiosaurus dolichodeirus and Pliosaurus brachydeirus than to Augustasaurus hagdorni". Ketchum and Benson (2010) also coined a new clade Neoplesiosauria, a node-based taxon that was defined by as "Plesiosaurus dolichodeirus, Pliosaurus brachydeirus, their most recent common ancestor and all of its descendants". The clade Neoplesiosauria very likely is materially identical to Plesiosauria sensu Druckenmiller & Russell, thus would designate exactly the same species, and the term was meant to be a replacement of this concept.