Basal (phylogenetics)

In phylogenetics, basal is the direction of the base (or root) of a rooted phylogenetic tree or cladogram. The term may be more strictly applied only to nodes adjacent to the root, or more loosely applied to nodes regarded as being close to the root. Each node in the tree corresponds to a clade; i.e., clade C may be described as basal within a larger clade D if its root is directly linked to the root of D. The terms deep-branching or early-branching are similar in meaning.

While there must always be two or more equally basal clades sprouting from the root of every cladogram, those clades may differ widely in taxonomic rank,[n 1] species diversity, or both.[n 2] If C is a basal clade within D that has the lowest rank of all basal clades within D,[n 3] C may be described as the basal taxon of that rank within D.[n 4] The concept of a 'key innovation' implies some degree of correlation between evolutionary innovation and diversification.[1][2][3][n 5] However, such a correlation does not make a given case predicable, so ancestral characters should not be imputed to the members of a less species-rich basal clade without additional evidence.[4][5][6][n 6]

In general, clade A is more basal than clade B if B is a subgroup of the sister group of A or of A itself.[n 7] Within large groups, "basal" may be used loosely to mean 'closer to the root than the great majority of', and in this context terminology such as "very basal" may arise. A 'core clade' is a clade representing all but the basal clade(s) of lowest rank within a larger clade; e.g., core eudicots.
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  1. ^ Heard, S.B.; Hauser, D.L. (1995). "Key evolutionary innovations and their ecological mechanisms". Historical Biology. 10 (2): 151–173. doi:10.1080/10292389509380518.
  2. ^ Engel, M.S.; Grimaldi, D.A. (2004). "New light shed on the oldest insect". Nature. 427 (6975): 627–630. doi:10.1038/nature02291. PMID 14961119. S2CID 4431205.
  3. ^ Fernández‐Mazuecos, M.; Blanco‐Pastor, J.L.; Juan, A.; Carnicero, P.; Forrest, A.; Alarcón, M.; Vargas, P.; Glover, B.J. (2019). "Macroevolutionary dynamics of nectar spurs, a key evolutionary innovation". New Phytologist. 222 (2): 1123–1138. doi:10.1111/nph.15654. hdl:10045/89954. PMID 30570752.
  4. ^ Baum, D. A. (4 November 2013). "Phylogenetics and the History of Life". The Princeton Guide to Evolution. Princeton University Press. p. 57. ISBN 978-1-4008-4806-5. OCLC 861200134.
  5. ^ Crisp, M. D.; Cook, L. G. (March 2005). "Do early branching lineages signify ancestral traits?". Trends in Ecology & Evolution. 20 (3): 122–128. doi:10.1016/j.tree.2004.11.010. PMID 16701355.
  6. ^ Cite error: The named reference Jenner2006 was invoked but never defined (see the help page).
  7. ^ Krause, J.; Unger, T.; Noçon, A.; Malaspinas, A.; Kolokotronis, S.; Stiller, M.; Soibelzon, L.; Spriggs, H.; Dear, P. H.; Briggs, A. W.; Bray, S. C. E.; O'Brien, S. J.; Rabeder, G.; Matheus, P.; Cooper, A.; Slatkin, M.; Pääbo, S.; Hofreiter, M. (2008). "Mitochondrial genomes reveal an explosive radiation of extinct and extant bears near the Miocene-Pliocene boundary". BMC Evolutionary Biology. 8 (220): 220. doi:10.1186/1471-2148-8-220. PMC 2518930. PMID 18662376.
  8. ^ McLellan, Bruce; Reiner, David C. (1994). "A Review of Bear Evolution". Bears: Their Biology and Management. 9 (1): 85–96. doi:10.2307/3872687. JSTOR 3872687.