Search results
Results From The WOW.Com Content Network
The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. [15] Ages of clades cannot be directly observed.
Botanical ranks categorize organisms based (often) on their relationships (monophyly is not required by that clade, which does not even mention this word, nor that of "clade"). They start with Kingdom, then move to Division (or Phylum), [17] Class, Order, Family, Genus, and Species. Taxa at each rank generally possess shared characteristics and ...
The term phylum was coined in 1866 by Ernst Haeckel from the Greek phylon (φῦλον, "race, stock"), related to phyle (φυλή, "tribe, clan"). [4] [5] Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as a group ("a self-contained unity"): "perhaps such a real and ...
Willi Hennig 1972 Peter Chalmers Mitchell in 1920 Robert John Tillyard. The original methods used in cladistic analysis and the school of taxonomy derived from the work of the German entomologist Willi Hennig, who referred to it as phylogenetic systematics (also the title of his 1966 book); but the terms "cladistics" and "clade" were popularized by other researchers.
An evolutionary grade is a group of species united by morphological or physiological traits, that has given rise to another group that has major differences from the ancestral group's condition, and is thus not considered part of the ancestral group, while still having enough similarities that we can group them under the same clade.
In this diagram, the clade labelled "Neornithes" is the crown group of birds: it includes the most recent common ancestor of all living birds and its descendants, living or not. Although considered to be birds (i.e. members of the clade Aves), Archaeopteryx and other extinct groups are not included in the crown group, as they fall outside the ...
The term sister group is used in phylogenetic analysis, however, only groups identified in the analysis are labeled as "sister groups".. An example is birds, whose commonly cited living sister group is the crocodiles, but that is true only when discussing extant organisms; [3] [4] when other, extinct groups are considered, the relationship between birds and crocodiles appears distant.
The diagram shows three common ways of doing this. For previously defined clades A, B, and C, the clade X can be defined as: The three most common ways to define the name of a clade: node-based, branch-based and apomorphy-based definition. The tree represents a phylogenetic hypothesis of the relations of A, B and C.