Contributions to Zoology, 66 (1) 3-41 (1996) SPB Academic Publishing bv, Amsterdam Conceptual issues in phylogeny, taxonomy, and nomenclature Alexandr P. Rasnitsyn Paleontological Institute, Russian Academy ofSciences, Profsoyuznaya Street 123, J17647 Moscow, Russia Keywords: Phylogeny, taxonomy, phenetics, cladistics, phylistics, principles of nomenclature, type concept, paleoentomology, Xyelidae (Vespida) Abstract On compare les trois approches taxonomiques principales développées jusqu’à présent, à savoir la phénétique, la cladis- tique et la phylistique (= systématique évolutionnaire). Ce Phylogenetic hypotheses are designed and tested (usually in dernier terme s’applique à une approche qui essaie de manière implicit form) on the basis ofa set ofpresumptions, that is, of à les traits fondamentaux de la taxonomic statements explicite représenter describing a certain order of things in nature. These traditionnelle en de leur et particulier son usage preuves ayant statements are to be accepted as such, no matter whatever source en même temps dans la similitude et dans les relations de evidence for them exists, but only in the absence ofreasonably parenté des taxons en question. L’approche phylistique pré- sound evidence pleading against them. A set ofthe most current sente certains avantages dans la recherche de réponses aux phylogenetic presumptions is discussed, and a factual example problèmes fondamentaux de la taxonomie. ofa practical realization of the approach is presented. L’auteur considère la nomenclature A is made of the three main taxonomic que taxonomique comparison ap- s’appuie, au fond, sur plusieurs principes de base. Neuf tels proaches hitherto developed, viz., phenetics, cladistics, and principes sont explicitement formulés, dont six sont taxono- phylistics (= evolutionary systematics). The latter term denotes les trois autres étant taxono- that tries the features miquement indépendants, an approach explicitly to represent basic miquement dépendants (donc compatibles seulement avec of traditional taxonomy and particularly its use of evidence certains concepts taxonomiques). La pratique taxonomique derived from both a similarity and the relatedness ofthe taxa courante montre taxon qu’un n’est ni une classe, ni un individu, involved. The phylistic approach has certain advantages in the mais bien un continuum (notion combinant des traits distinctifs answering ofthe basic aims oftaxonomy. de la classe et de l’individu) de subtaxons, continuum séparé Taxonomic nomenclature is found to rely ultimately on a d’autres continua lacune. On considère le par une que concept few basic principles. Nine of these principles are formulated du type est le meilleur instrument à notre disposition s’il s’agit explicitly: six ofthem are taxonomically independent, and three de travailler avec le concept taxon-continuum. are taxonomically dependent, that is, they are only compatible with taxonomic particular concepts. Judging from current taxonomic practice, a taxon is neither a class nor an individual, but continuum notion a (a combining some features ofboth the Introduction class and the of subtaxa that is delimited individual) by a gap it from other such continua. separating The type concept is scientists do not take much notice of found be the best Frequently, to available tool to operate within the concept the of their How- of the taxon-continuum. methodological grounds work. ever, when the standard means and methods of the work time after time fail to yield satisfactory re- Résumé sults, one is tempted to raise a kind of scientific revolution (Kuhn, 1970), i.e., to abandon those tra- and methods with Les hypothèses phylogénétiques sont élaborées et vérifiées ditional means along the under- (normalement de manière implicite) sur la base d’une série de lying methodology and to replace them with some- d’autres d’assertions décrivant présomptions- en mots, un different. scientific thing Revolutions, even ones, certain ordre de choses dans la nature. Ces assertions doivent in rarely pass bloodless, that they usually result in être des à acceptées comme telles, indépendamment preuves rejecting certain approaches that are in fact work- leur mais seulement en l’absence de soli- appui, preuves assez able, albeit in a somewhat different while des contre leur validité. On discute une série de présomptions domain, phylogénétiques des plus usuelles, et on présente un exemple the data obtained by means of these approaches concret de réalisation en pratique de cette manière d’aborder le still be and may meaningful worthy of being reas- problème. - 4 A.P. Rasnitsyn Phylogeny, taxonomy, and nomenclature sessed rather than rejected. That is why it seems Phylogeny preferable to examine the methodological back- of Each in ground a scientific approach prior to abandoning step cognition, while knowledge is ac- in the and its meth- it, hope to recognize improve quired, in my opinion proceeds through four suc- and thus the cessive known odological deficiency to safeguard ap- stages. First, we start seeking for and the results of This is the elements in proach its application. an essentially unknown (i.e., not yet of objective the present publication. understood) pattern. On the basis of previous expe- and/or the rience results of a preliminary confron- issues forced Two separate me to approach the tation with the pattern, we then sort these known elements methodological problems of descriptive biology. as either important (i.e., relevant to the One the crisis of that In was long-lasting taxonomy goal set), or as unimportant. this context, the resulted in the continual between "tradi- known conflicts elements of an essentially unknown pattern and the - the tional" rival are considered when that taxonomy approaches important we suppose our the Because of it phenetic and, later, cladistic ones. of knowledge permits us to discern (i.e., is corre- of of an intuitive a traditional lated or otherwise reflects in feeling superiority with, one way or an- I in taxonomy, was involved this controversy, al- other) important features of the pattern. In turn, the without much though success (Ponomarenko & important features are those that have a more pro- found influence Rasnitsyn, 1971; Rasnitsyn, 1972, 1983a, 1987a, on, or are correlated with, or & 1988b, 1992a; Rasnitsyn Dlussky, 1988). Re- otherwise permit us to appreciate and foresee, the sults of my attempts to develop my arguments are structure of the pattern and its behaviour under below in the presented chapters devoted to various circumstances. For example, when an en- and phylogeny taxonomy. tomologist wishes to instate an in his opinion en- As the is different regards nomenclature, cause tirely new group as a separate taxon, he must also in that it is rooted in deal with my paleontological experi- the classificatory aspects of his proposal ence. Despite the long history of taxonomy and no- (I mean only the internal classification, not the menclature, I believe the basic principles of no- general taxonomie position of that taxon). In this menclature are only partly understood and formu- treatment he will disregard features, how signifi- lated as such. Some of these are sim- that discriminate principles so cant per se, males and females, or and self-evident that their existence and adults and larvae it ple appli- (except when comes to subdi- cation is the in perceptible only in peripheral areas of tax- vide taxon question and to classify each sub- When one has to difficult and onomy. classify objects group separately eventually to compare the re- deficient in taxonomically important characters (or sults with other data). In addition he will tend to one is often forced break the even lacking them), to give preference to morphological similarities over rules of in nomenclature. This is common practice such features as colour patterns. in the of immature paleontology, study parasitic The second stage of cognition begins here. One of where worms, or asexual stages of fungi, a stu- creates a hypothesis concerning the particular dent cannot normal escape violating taxonomie similarity between the patterns under examination practice and breaking the rules of nomenclature. and a class of patterns that previously had been An of this little experience sort gives satisfaction studied already but seemed to be dissimilar to the until the student to discern begins more deep- patterns in question. The supposition ought to be seated reasons why he has not followed the it should gener- predictive, i.e., propose the existence of a rules. the ally accepted The reason why is that un- particular mechanism that is responsible for the derlying principles of nomenclature are incompat- similarity, or it must clarify why there is also a ible with the deficient material that taxonomically similarity in many other characters. This subse- nevertheless must be classified. This controversy quently allows us to hypothesize that the similarity renders these basic thus principles discernible, per- can predict the behaviour of the pattern in question their identification and mitting study (Rasnitsyn, in various environments and conditions. To con- 1986; 1992b). tinue with the above example, the taxonomist will Contributions to Zoology, 66 (1) - 1996 5 that the in possibly pose similarity morphological tion are impossible, we can never be certain of any characters could indicate a higher (say, generic) of our observations and considerations concerning level of the overall while the similar col- similarity, the nature of things. If