2004/02/01 by Michel Laurin, Jason S. Anderson · 4 citations
Earth and Planetary Sciences · Mathematics · #Evolution and Paleontology Studies #Paleontology and Evolutionary Biology #Morphological variations and asymmetry
paper · pdf · doi:10.1080/10635150490264716
openalex publication_date 2004/02/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/22
This exchange stems from an on-going debate between advocates of crown clade (e.g., Gauthier et al., 1988; Rowe, 1988; Laurin, 1998) and those of apomorphy-based (e.g., Ahlberg and Clack, 1998; Lee, 1999; Padian et al., 1999; Anderson, 2001) definitions of widely used taxon names (see Table 1 for a glossary of terms). Both types of definitions have advantages: apomorphy-based definitions usually retain a composition of taxa similar to that proposed in most paleontological studies (Lee, 1999), whereas crown clade definitions correspond more closely to the usage of these names by comparative biologists working on extant taxa (de Queiroz and Gauthier, 1992; but see Bryant, 1994; Lee, 1996). Here, we concentrate on the name Tetrapoda, which has been the subject of recent discussion (Anderson, 2001, 2002; Laurin, 2002), but many of the arguments presented here could be applied to other widely used names, such as Mammalia, Aves, and Vertebrata. Glossary of terms used in this exchange Glossary of terms used in this exchange Laurin (1998, 2002) adopted the crown clade definition of the name Tetrapoda (the last common ancestor of amniotes and lissamphibians, and all its descendants) proposed by Gauthier et al. (1988). Anderson (2002) objected to the crown clade definition of Tetrapoda and, following Lee (1999), advocated adoption of an apomorphy-based definition of this name (the first sarcopterygian to have possessed digits homologous with those in Homo sapiens, and all its descendants). The following exchange is aimed at clarifying the respective advantages of both types of definitions. Established usage of taxon names is important because the systematic community will soon define many widely used names, and the PhyloCode (Cantino and de Queiroz, 2000) recommends, when defining a name, to disrupt current and historical usage as little as possible (Recommendations 10A, 11A). Furthermore, as stated by Anderson (2002: 824), “the PhyloCode provides mechanisms for the amendment (Article 13) or suppression (Article 15) of definitions with priority if they should contravene long accepted usage and thus create instability in nomenclature.” These considerations are important because name definitions under the PhyloCode delimit taxa (i.e., determine their inclusiveness when applied in the context of a particular phylogenetic hypothesis), whereas definitions under traditional rank-based codes do not. Within the traditional rank-based nomenclature system, debates about the inclusiveness can go on indefinitely, whereas within the PhyloCode system, such debates will be minimized (given a particular phylogenetic hypothesis) after the International Committee on Phylogenetic Nomenclature (ICPN) determines which of two conflicting phylogenetic definitions, or names with the same definition, should be retained. The ICPN will have ruling authority (although we expect such actions will be rare if the rules of the PhyloCode are followed, similar to current practice under the International Code of Zoological Nomenclature), but it is more productive to discuss various competing definitions prior to the implementation of the PhyloCode. By ensuring that the most appropriate definition becomes established at the initiation of the PhyloCode system, much future controversy and ICPN action can be avoided. The case of the name Tetrapoda is not unique. Similar disagreements between proponents of crown clade and apomorphy-based definitions have involved several other widely used names, such as Aves (reviewed by Gauthier and de Queiroz, 2001) and Mammalia (Rowe, 1988; Desui, 1991; Rowe and Gauthier, 1992; Wible and Hopson, 1995; Ji et al., 1999; Sidor, 2001). Thus, the current debate on the meaning of the word Tetrapoda can serve as a case study that may help with the resolution of similar disputes in the future. In this point–counterpoint, we debate four key issues related to the definition of the name Tetrapoda. LAURIN: Anderson (2002: 825, emphasis added) stated that although there is a physiological component to other names such as Aves (Gauthier and de Queiroz, 2001) and Mammalia (Rowe, 1988) that justifies the restriction of those names to the crown, no such component exists for Tetrapoda. The defining feature of tetrapods is based in hard anatomy easily preservable and observable in the fossil record. A survey of a dozen biology books shows that in most cases, a of the definition of the name Tetrapoda tetrapods or or in the of these is a a that is not This is important because the is for crown tetrapods but not for with digits and Clack, 1991; Laurin et al., This the of Laurin or other such as those of Gauthier et al. or et al. are accepted The physiological and or with a are to but they not and many the of the digits and Laurin, The that the name Tetrapoda is closely with a and that this the crown but not the clade of that digits in of a crown clade definition of the name Tetrapoda. of of various that are to a 1 of the between the and the of this of the have many physiological of the digits and by in and or of the of the at in the of the and on (the of of is to and may be that of of the to most of the much of which the the in the of the to see in by the of in the of the of the and of of a a by two other in The and and Laurin and In many and that of et al. extant are a of but this not the or of of this the of the crown clade definition of the name its is with an The of apomorphy-based Tetrapoda is of the taxa in this are from the a of with in the but from the the first that may have with but no digits are and the first with with and and of an a of to long by many as to and a of and to and and by to be to or all are the clade and their the clade the clade and the clade and of the and and and and and that is closely with a as a defining In the phylogenetic taxa and within or by the of both and The key of Tetrapoda its has been the with and as the for the of the by is not to a it is a with a of that is with a of a much between (the in a and (the for those used in the of an apomorphy-based definition for Tetrapoda the feature with which it is long the is that this definition is of of (e.g., it not for this we not be to of with phylogenetic and as recent fossil and Clack, that the of is from both in of the of and the of the crown thus not a of the is a not a that between the of the and the of the crown that although is not to the discussion at of the apomorphy-based definition of Tetrapoda is historical a of the PhyloCode. In to this debate (Anderson, 2002), an emphasis on historical with to the name Tetrapoda. such as Mammalia and Aves the key of and physiological that can be in the Thus, from the of historical it could be that those names should be to the crown, because in the crown have been with the Tetrapoda, a key that not easily preservable in the fossil record. key the from the of historical it is to define Tetrapoda in to the of the the and digits are can the or of this feature in the fossil record. This is and easily and its is phylogenetic The of is the of much the clade of a name for of not the name that is to this clade and is in with this LAURIN: survey shows that a of that is a defining feature of as is a defining feature of and in all these cases, there are other defining and for the and for the for and of these are not to be a or a if that to of the after they in an this not be from that of for the and of in and in to be a defining feature of Aves and Mammalia, see no to the between and the name Tetrapoda. an between tetrapods and which have but stated in of to be a key to is of its in of do define is in the fossil as key in the and emphasis added) the feature of the first tetrapods as on may have thus to for an The little more a on have been the from its it LAURIN: that the most important key feature of tetrapods is the of two similar could be for and or the or for and the is a to the of these Thus, the key of tetrapods is the but in many of the that have the between tetrapods and about as as that between and or may be of as an for the of the such an has been but has been of as an for the of in as by the following of the for their and are those of the most Thus, that the between and tetrapods is similar to that between and and although it may be in the there is a it is in but not in LAURIN: (Anderson, that all of Tetrapoda as a taxon name, that by it and other This is not the as an in the of of not used to and the all of the it is of the in which the word can be A for the word of which the word in a meaning (the other other with four The word in the of a of these The same survey has on that to of an apomorphy-based definition of the name Tetrapoda should be A of the that in the recent the current the word has been used in an that is based crown clade based in about of these studies The meaning of the word is with a in A crown and with the word but in the studies in which the meaning of this not stated but could be it to a crown clade in the of of see the of the not these This is not because the is with about the of or other of that do not of the have the of such not a the various of the word and most of of these but by the of such can be to to crown Thus, if their meaning is most about tetrapods the crown In the following to the meaning of the word in the These the to 2002) the word in the key or The the various of the word 1 crown when a in the about tetrapods to the crown but to crown when the not to to but when the on of that can be in extant such as when no in the to which of the but to a between the of and the word tetrapods or when taxa tetrapods do not to the crown when a about tetrapods to the first or to that all The the of on of in the of on a of (the first on the that in the of the the of the or the of of the in the of The is based on the of these whereas the is based on the on paleontological studies the paleontological studies in as in a and on studies the studies in The working on those working on the of hard and a The of the with taxon is not paleontological if there are physiological other between a taxon and its there are advantages in the name of that taxon to a crown of that usually be in could names, to more names they are or to that these may not have been in the first of the be to names for the crown and a definition to the paleontological for widely used names, but it to expect that most and other working with extant taxa the This survey of the that most do not with such as by the of studies in which the of the word The name by which more or with the crown of tetrapods under the that has not been used by other A of the the to for all of this name to a names that have been proposed for crown such as used by have not been used Gauthier and de Queiroz that the Aves or used in in the Zoological for the whereas the word used in for the same Furthermore, the adoption of names for crown not the of the about to the crown in the the meaning of these names be the proponents of Phylogenetic Nomenclature the on extant taxa will many about the of and and if the definition of these names not correspond with the crown many of the in that will be The meaning to the word in the paleontological to from that in the In most paleontological a of the word is but in it is the crown clade that most to established usage This has not been (Lee, because most do not to be with the meaning of the word and they that tetrapods such as are but the that they the name is with this as de Queiroz and Gauthier Thus, although the apomorphy-based that to be in it not to in most This is if usage of the word is is to an apomorphy-based definition of the name Tetrapoda, but their of this name is with such a definition and the of (the of a name for more usually two or more not the of a in a paleontological because all biologists used Tetrapoda as to the name, a it is not not about the of Tetrapoda as a taxon name, but study of current usage in biology is based a of the word and not the is little that the of that is used in the is because there is little the should these define this in the A of the of for the Tetrapoda the same as a of of these are (Anderson, 2001, 2002), and is 2002), the can the used current In Tetrapoda used in the of a and 2001) and not The are the meaning can be from the et al. the of Tetrapoda to in the which to the of the of and not the et al. Tetrapoda to a and the (2002) to Tetrapoda in the traditional for Tetrapoda issues that should be that tetrapods such as are with this and it is by of the of Tetrapoda. to this the of the studies in in studies by the same a of to which survey of the is by and Tetrapoda. have on extant on two on both but extant and on both but The in taxa of the of the of names by or many biologists on both and fossil taxa and are to issues related to the study of The of when they the name and when they the name Tetrapoda. a and Tetrapoda in to the crown two more the of Tetrapoda as a of the the crown meaning of Tetrapoda on extant and on two two it is important that Tetrapoda and to the same but and it is important in and do not it at This survey that a of when they the of the of taxa and a not it is important that the with the The usage in the a biologists of the name should they the to survey used the of the is if that studies of or other of that do not to the crown because the of these be in fossil This that for study in fossil taxa will which is not of of have been (e.g., et al., the of the are not the studies to fossil taxa or they more the taxon name Tetrapoda. do their to fossil taxa the feature of but it is that their discussion is or they do not when they their (although is not because it be it is a the and a The more important to in is the first by Lee be that based extant to crown Lee the of which are not in crown but for an two there has been much recent the of in and the in related to from crown but be this these of the crown do not that we should to the widely accepted meaning of an established name because the of of the crown can be in the apomorphy-based Tetrapoda, has a stated to the The or of the can be in the fossil it is on in at the crown but at the it is Furthermore, an apomorphy-based definition for Tetrapoda is with historical and current of both the and to it is a crown clade an apomorphy-based definition for Tetrapoda that will to the of the and to in most biologists the same when they or LAURIN: by that a on the word on the name Tetrapoda and by that biologists the same meaning to both with last in be if we could no as with or as with to but two that most biologists when they the word but that is not they in most cases, they the crown that they This that is in The of are by of the meaning of the word Tetrapoda in the because in the meaning of the name Tetrapoda in at of the that in the of is from the meaning is not which shows or the meaning of the name Tetrapoda is in this that et al. to the of the to define the name Tetrapoda. the for the of this taxon is in the and it by more the fossil from the The used by et al. from the by et al. that is the et al. not they by but they that this from the fossil record. with the of the this to the between that and that because the of this clade from that Thus, et al. used a of Tetrapoda, not an apomorphy-based (2002) to Tetrapoda defining but the crown, because all from extant et al. Tetrapoda and the crown, but the not Thus, in about Tetrapoda in the that do not to the clade of This discussion shows it in many cases, to which clade is under the name or Tetrapoda in the do not that for study in fossil taxa will that that are about such that are to be to the crown because in the of the on which such are based are to the The that a to a more clade the crown not a that tetrapods if to the this (the not be to The is more because if a stated to be of tetrapods as and to be to a of that clade (the crown, for the be This not widely in Lee that these to the crown at which these have and proposed a similar that crown be as more because their if we to of the there is an to names for crown because many in the can be for crown but be for more Thus, these are in the context of crown but not in the context of if of these that be to of or of as many of could to be if widely used names to more the crown The of in taxa can be but is the of the of an in by Lee and by Lee and Laurin and with this these et al., et al., et al., 2001) as The of the used Tetrapoda in a et al. but not to have the meaning of the the are the same et al. with in this et al. used the same terms and as et al., for the of by et al., which is an of et al., which that it a by et al., 2001) or that they the taxon to tetrapods to be for this not from their a clade from that by when the word and thus is not to as this the usage of et al. more they the of et al. to of or they Tetrapoda in a as The case when that the definition has little in the The two in survey a definition are from the same and are the with have the of LAURIN: are in the to and with that in most cases, this is the apomorphy-based they from a to a crown and is in paleontological the apomorphy-based the tetrapods and Tetrapoda for these apomorphy-based and crown that in many it is not which of these they that in of can be but that the name to the crown is the to this is at the of we and we this it that of the issues is current in are the of taxa are for after most on the are are there is no on the of the of because of a in the fossil at the Similar to there is a of taxa at the These taxa are for and we should the name Tetrapoda to the crown we a feature to tetrapods that is to be to a in the discussion of apomorphy-based definitions and key it to be that we do not name taxa by the they an feature but to the particular ancestor that the The of preservable or not in the fossil will with phylogenetic it not if of because this all of the LAURIN: is that the of of as are but that is not the that the crown the may have the crown, is a that an apomorphy-based taxon that may be to the crown is and may be this is a of between that in of of are whereas to the of such a The to are no which definition of Tetrapoda is fossil taxa at the will but most crown taxa have not been future shows that a not have a particular feature that been to the crown, the is and a to the crown or the crown, of will the of the of to all In the of survey a of the used in a a study the name Tetrapoda (the of it used in all other the word a to to the clade has not been In the of this discussion it has that there is a in In the case of such as there is a between and that the is used to in This is for more names or names used in phylogenetic but names have the of historical usage and such as have the This is the PhyloCode historical in these by in of the and are appropriate because the phylogenetic definitions for and are with historical that long a has been from as there is no between the and of the by adoption of a crown clade definition of Tetrapoda. with that should be in and terms the context is not all of this is future discussion on this subject with the community be LAURIN: about the crown can be but such usually the most of By most about tetrapods in the and physiological are not by Furthermore, a by and on in both of a clade is to be is a based on a of and that not the two of a Thus, although both types of can be the of will be for an apomorphy-based Tetrapoda for those for a crown clade Tetrapoda. do not that the of the in the to to the this the have that their to most or but such are that the of is by is not LAURIN: is in the current because at four types of are those that have on the the those that are to have with the those that are in the crown but that can be to have with the they are involved in the of the and those that are in the crown and for which there is no to that they much to all four and if we can of such we The name Tetrapoda the has been used in the and in the paleontological have the crown, whereas have the clade of of the apomorphy-based definition will this meaning to The that will a name as to to the crown is by the of such terms (e.g., if we adopted the crown clade definition of the name Tetrapoda, it and name for because most are of the between these two This is the most to the name Tetrapoda a meaning in the of meaning in the and of meaning in future paleontological and a crown clade definition be most the arguments that have presented to have the meaning of the word but nomenclature should be and a that will a meaning to taxon The current usage of the Tetrapoda the is to the of the usage of this name if we both and Thus, it will be to the meaning of a widely used taxon name it is under the PhyloCode by that the established definition not correspond to the established at when that definition with the usage or that or The same for most widely used names (e.g., Aves, that have been crown clade definitions. The may have to the and and 15) of the PhyloCode historical or established usage of taxon names, because this exchange shows that the established usage of a name is from in the of phylogenetic it has been that an apomorphy-based definition the historical usage of Tetrapoda (de Queiroz and Gauthier, about the of apomorphy-based definitions as they and about to the adoption of a crown clade definition (Gauthier et al., 1988; de Queiroz and Gauthier, The current of the of the in has (Lee, 1999; and de Queiroz, and the has been and 1994; Lee, Lee and a apomorphy-based definitions are more by those (Gauthier and de Queiroz, 2001). that there is no for the crown clade definition for Tetrapoda when there is a much apomorphy-based definition for Tetrapoda the historical meaning of historical a the that there is in the for which will future apomorphy-based Tetrapoda is a and to all current of phylogenetic The has its is phylogenetic the in is it can be in the fossil and we can about the of a subject of current Furthermore, an apomorphy-based definition for Tetrapoda most their the name, most biologists the is usually in the and the the The of the of the and in usage which is the of it may be to the of phylogenetic nomenclature if we the meaning of this name when it can easily be the phylogenetic in a that its historical but of are of the biologists have of the a has applied its in The to the of is to all biologists about the of in name and not to the of and widely names because we to expect that most and other working with extant taxa the all to and and for many and and the and of for of this Bryant, Lee, de de Queiroz, and de and for to this Both and for their of this The in the following discussion that of that to a crown clade and studies that that are of the crown clade but that be in with as a crown clade definition of the word In several cases, the meaning of the word more and of which used more The used to such studies but a are that that more to to the crown to the taxon studies such as that of et al. stated that the is within the as in this has been in all The between in a and a to a crown Furthermore, comparative studies in which extant taxa but for which the word used to discuss these taxa or the clade that to a to the crown to a when the The that has been adopted this survey not to the to but they do In many the meaning to the word be and could to the crown as to the This studies such as that of and stated that “the and of in the have in the of of This provides an between the of and the taxon Tetrapoda as in several other the word is with the word with the word but the of is in the crown, and the of the clade that is to is not have been of of the word that are to the to the crown the by et al. stated that most the of the to tetrapods on the of the to we be that the first used their extant but it to that the of digits and of other of the be closely with the in that the or of with the word to a Thus, the study of et al. in this because they stated that “the and the and because the between and is with the of In the word used in a and to and in the word not as a key These two have been from and are not