Sources
open directory project
Help build the largest human-edited directory on the web.
Submit a site - Become an editor
Wikipedia. Licensed under the GNU Free Documentation License.
Are you an expert in this subject? Join the discussion and share your knowledge at Wikipedia.org.
Stem group
From Wikipedia, the free encyclopedia
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. Stem groups are by definition paraphyletic but can be defined because of the objective definition of the crown group they give rise to. The terminology of subdivision of stem groups has proved difficult. Jefferies proposed that the smallest paraphyletic units of the stem group were plesions; and that the crown group could be successively enlarged by addition of more and more basal plesions to form larger monophyletic groups called scions. However, this terminology (especially scions) has not widely been used.
 |
This paleontology article is a stub. You can help Wikipedia by expanding it. |