Linnaeaii, Rank-Based, and Phylogenetic Nomenclature: Restoring Primacy to the Link Between Names and Taxa Kevin De Queiroz
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Linnaeaii, rank-based, and phylogenetic nomenclature: Restoring primacy to the link between names and taxa Kevin de Queiroz de QueiroK, K. 2005. Linnaean, rank-based, and phylogenetic nomenclature: Restoring pri- macy to the link between names and taxa. - Acta Univ. Lips. Symb. Bor. Upa. 33:3, 127-140. Uppsala, ISBN 91-554-6192-1. Linnaeus and other 18"" Century naturaii.sts practiced nomenclature in a way that associated laxon names more strongly with taxa (group.s) than with the categorical ranks of the taxonomic ("Linnaean") hierarchy. For IS'"* century naturalists, ranks functioned merely as devices for indicating hierarchical position that did not alTccl I he application of taxon names. Conse- quently, taxa did not change their names simply because of changes in rank. For example, the name RepiiUa did not change when the rank of the taxon designated by that name was changed from order to division or class. During the 19''' Century, a different approach to nomenclature emerged that made rank assignment centra! to the application of taxon names. Under this rank- based approach, which forms the ba.sis of the current botanical and zoological ctxlcs, names are implicitly defined in tenns of ranks and types and are therefore more strongly associated with ranks than with the taxa to which they refer. Consequently, taxa change their names simply because of changes in rank. Forexample, if the rank of die taxon/Icícacrae is changed from family to .subfamily, its name must change to Aceroklnae. Phylogenetic nomenclature is a new approach that ties taxon names to explicitly evolutionary concepts of taxa through definitions that describe taxa in terms of ancesu-y and descent. This approach once again associates ia.\on names more strongly with taxa than with ranks and thus represents a return, updated with evolutionary principles, to an approach similar to that practiced by Linnaeus and other 18'''Century naturalists, Kevin de Queiroz. Departivem of Vcrtebrati' Zoology, National Museum of Natural Hislory. Smitksoimin ¡n.^titulioii, Waxliinf^ton. DC. 20560-0162. USA. E-mail: dei/ue iik^ai. edu In addressing the future of biological nomencla- fundamental difference, phylogenetic nomencla- ture, it seems appropriate to consider phyltigenetic ture often differs significantly from traditional notn end ature (e.g. de Queiroz and Gauthier 1990, rank-based nomenclature concerning which 1992, 1994, de Queiroz and Cantino 2Û()lb) - a names are to be considered synonyms and homo- new approach to biological nomenclature in which nyms, and thus also the accepted names of partic- the application of laxon names is based on explic- ular taxa. Although phylogenetic nomenclature itly evolutionary methods. This approach contrasts can be considered radical in this respect, in other with the traditional rank-based approach - adopted respects it is not radical at all but instead represents hy the current Bacteriological (lUMS !992), Zoo- a return to an approach similar to that practiced by logical (ICZN 1999), and Botanical (IBC 2000) Linnaeus and other early naturalists. codes - in which evolutionary considerations are In this paper, I will discuss the relationships be- entirely taxonomic (i.e. they determine only what tween 18'" Century, rank-based, and phylogenetic kinds of groups are to be recognized as taxa), and nomenclature, emphasizing the relationships be- nomcnclatui c (i.e. the use of taxon names) is ba.scd tween taxon names, on the one hand, and taxa on categorical or taxonotiiic ranks. Because of this (groups) versus categorical ranks, on Ihe other, I Symb. Bot. Up.'í. 33:3 128 Kevin de Queiroz will first describe how nomenclature was practiced categories, they use those categories in a way that hy ¡8"' Century naturalists. In particular, I will differs significandy from the way in which the cat- provide evidence thai the primary associations of egories were used by Linnaeus and other early tax- taxon names were with taxa (groups) rather than onomists. with ranks (laxonomic categories). I will then de- I have called attention to Linnaean nomencla- scribe the rank-based approach to nomenclature ture both because of the importance of Linnaeus' thai emerged during the 19"^ Century and forms contributions to taxonomy and nomenclature and the foundation of the currcni international codes because this paper is part of a tribute to one of his (e.g. lUMS 1992, ICZN 1999, IBC 2000). In par- great works, the Species PiiinUintm. Nevertheless, ticular, [ will describe how the rank-based ap- the approach thai I really wish to describe is not proach changed the primary associations of taxon the approach of Linnaeus in particular hut that of names from taxa to taxonomic ranks. Next, I will 18''' Century European naturalists in general - or describe the recently proposed phylogenetic ap- more specifically, that of European naturalists proach that forms the basis of the draft fAy/wCoi/e from the time when they adopted the use of cate- (Camino and de Quciroz 2000, 2003), giving a gorical ranks, following Linnaeus, until sometime brief overview of its similarities to, as well as its in the middle of the 19"' Century, when the alterna- differences from, traditional rank-based nomen- tive rank-based approach to nomenclature clature. Finally, 1 will describe how the phyloge- emerged. netic approach restores the primary association be- In describing how nomenclature was practiced tween names and taxa. Although phylogenetic no- by Linnaeus and other eariy naturalists, the point I menclature de-emphasize s taxonomic ranks, want to make is that for these eariy taxonomists which are commonly considered one of the hall- taxon names were more clo.sely associated with marks of Linnaean taxonomy, 1 hope to show that taxa than with categorical ranks. This point can be this new approach is, with respect to the function demonstrated by showing that when particular of categorical ranks, more similar to nomenclature taxa (groups) were assigned to different ranks, the as it was practiced by Linnaeus and other early names of those taxa did not change and thus re- naturalists than is the later rank-based approach tained their associations with the taxa to which that underiies the current codes of botanical and they originally referred, rather than with the ranks zoological nomenclature. with which they had previously been associated. To dcmonslrate this, I need to adopt a conceptual- ization of taxa that approximates that of 18* Cen- Linnaean and Late IS"" Century tury naturalists.Therefore, I will adopt aconceptu- Nomenclature ahzation of taxa as sets of organisms, particulariy I will use the term Linnaean nomenclature for the those sharing distinctive characters (see de Quei- nomenclatural principles and practices adopted by roz, 1997). Carolus Linnaeus (1707-1778). Linnaean nomen- Because this symposium commemorates the clature in this sense should not be confused with publication of Linnaeus" Species Plaiiiaiuin, I the taxon names used by Linnaeus, which is Lin- wouid have liked to use names from that work to naean nomenclature in a ditïerent sense. More im- illustrate my point. However, 1 am a zoologist, portantly, it should not be confused with the no- which is to say that I am sufficiently unfamiliar menclatural approach that forms the basis of the with the historical use of plant taxon names that current international codes of nomenclature. Al- using those names as examples would have greatly though these codes are based on the taxonomic delayed the completion of my paper. For this rea- rank-categories adopted by Linnaeus (i.e. regnum, son, I will emphasize zoological taxon names, par- classis, ordo, genus, species) with the addition of ticularly those of vertebrates, the group with which both primary (e.g. division, phylum, family) and I am most familiar. secondary (e.g. subclass, inlraorder, superfamily) In addition, it is not particularly informative to Synih. Bot. Upx. JJ:J Linnaeun, rank-based, and pkylogeneiic nomenclature 129 compare Linnaeus' use of taxon names with use of Class Amphibia Tribe Amphibia the same names hy earher authors, at least not as Order Reptilia Division Replilia they relate to differences in rank assignments. The reason is that taxonomic ranks were used infre- Figure I. Application of taxon names by late 18''' and quently by earlier authors; their consistent and sys- early 19'" Century naturalists. For ihesc early naturalists, tematic use derives largely from the work of Lin- categórica! ranks served to indicate the nested or mutu- ally exclusive relation.ships of taxa but had no effect on naeus, Therefore. I will illustrate my point with the application of taxon names. Therefore, a taxon could zoological names used by Linnaeus and later 18'*' be designated by the same name regardless of the rank to and early 19"' Century authors. Of particular inter- which it was assigned. In this example, the same names. est are cases in which a taxon recognized by Lin- Amphibia and Replilia, were used by Linnaeus (e.g., ] 758, 1766) for nested taxa thai he ranked as a class and naeus (or some other author) was also recognized an order (left), and by Scopoli ( 1777), who ranked the by a subsequent author but assigned to a different same taxa a^ a tribe and a division (right). taxonomie rank. [n these cases, the change in rank did not re- quire a change in the name of the taxon. I do not These taxa were once again excluded from Am- mean to say that the names of taxa never changed. phibia in the 13"" Edition of Ihe Systema Naturae Authors who recognized taxa of similar or identi- (Linnaeus and Gmelin 1788). (1 have not at- cal composition but based their taxonomic systems tempted a thorough survey of the various editions on different characters often gave different names of Linnaeus" Systema Naturae but instead have to those taxa, since it was common to use taxon chosen the hrst ( 1735), sixth (1748), tenth ( 1758), names that described the characters upon which and twelfth (1766) editions as the sources of my the systems were ba.sed.