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Stem and crown group terminology
Total group (also total clade, stem clade, or panstem clade) is a term used in systematics to refer to a crown clade plus its stem group. It thus refers to all organisms sharing more recent ancestry with a group of living organism (extant members of the crown clade) than with any other living organisms. Basal members of total groups show few distinguishing features from related groups, and may thus be hard to assign to the total group. More derived members, however, show increasing numbers of synapomorphies of the crown group.

Terminology

When referring to a systematic grouping, there is a danger of confusion between the crown and total groups, although they mean different things. For example, simply referring to a fossil as a "bird" does not tell you whether it is a familiar example derived from the last common ancestor of all living forms, or whether it is a more basal form. (By definition, all living forms fall into the crown group.)

Since all total groups correspond to a crown group, some systematists have suggested using a standardized prefix (e.g., Pan-) to form names of total clades from the names of their corresponding crown clades. For example, Panmammalia (or Pan-Mammalia or pan-Mammalia) would be the total clade including Mammalia but no living non-mammals. Others have pointed out that there are already names for many total clades; for example, Synapsida and Theropsida have both been used to refer to the total mammalian clade.
Biological systematics is the study of the diversity of life on the planet Earth, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: phylogenic trees, phylogenies).
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For the phylogenetic group, see .
The Crown Group is a catering and event caterer in the United Kingdom. The London-based company began in 1978 as a collection of chefs in an agency that supplied local caterers with relief chefs.
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In palaeontology, a stem group is a systematic grouping that is required to accommodate fossils in the classification of organisms. A stem group lies basally to a crown group, consisting of its most closely related living relatives.
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Plantae
  • Chromalveolata
  • Heterokontophyta
  • Haptophyta
  • Cryptophyta
  • Alveolata

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    • Extant is a term commonly used to refer to taxa, species, genera or families that are still in existence (living). For example, Brandt's Cormorant is an extant species, while the Spectacled Cormorant is an extinct species.
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    In evolutionary biology, a synapomorphy is a derived character state shared by two or more terminal groups (taxa included in a cladistic analysis as further indivisible units) and inherited from their most recent common ancestor.
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    For the phylogenetic group, see .
    The Crown Group is a catering and event caterer in the United Kingdom. The London-based company began in 1978 as a collection of chefs in an agency that supplied local caterers with relief chefs.
    ..... Click the link for more information.
    Biological systematics is the study of the diversity of life on the planet Earth, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: phylogenic trees, phylogenies).
    ..... Click the link for more information.
    Mammalia
    Linnaeus, 1758

    Subclasses & Infraclasses
    • Subclass †Allotheria*
    • Subclass Prototheria
    • Subclass Theria

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    Mammalia
    Linnaeus, 1758

    Subclasses & Infraclasses
    • Subclass †Allotheria*
    • Subclass Prototheria
    • Subclass Theria

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    Synapsida *
    Osborn, 1903

    Orders & Suborders
    • '''Order Pelycosauria *
    • Suborder Caseasauria
    • Suborder Eupelycosauria *
    • Order Therapsida

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    Synapsida *
    Osborn, 1903

    Orders & Suborders
    • '''Order Pelycosauria *
    • Suborder Caseasauria
    • Suborder Eupelycosauria *
    • Order Therapsida

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    This article or section needs copy editing for grammar, style, cohesion, tone and/or spelling.
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