摘要
修订版Treatise双壳纲卷首卷即将正式出版,其分类系统的纲要已提前公开发表。在古生物学家、现代生物学家和分子生物学家的共同努力下,终于顺利地实现了化石和现生双壳类分类系统的初步融合,与1969版的形态分类相比,整个分类系统已经面目全非。为此,有必要全面介绍其分类方法和原则,介绍新分类系统带来的种种重大变化。新分类系统将进化学派的系统发育概念与分支系统分析方法的合理内核有机结合,发挥后者在方法论方面的优势,摒弃其系统发育即分岐演化的错误概念和某些不合理的分类学原则,如拒绝接受并系群和姐妹群必须具有相同级序等;充分发挥林奈系统的长处并加以改进,形成由共同衍征主导同时也考虑前进演化的林奈式级序体系,准分支系统分类方法由此形成。新方法兼顾分支发生和进化级这两个不同的方面,注重恢复可能的祖-裔关系;主要根据系统树但借鉴分支图方法来确定级序格架,将级序与系统树的分枝点对应,即与衍征的分歧时间对应,使级序的划分不再主观任意;一般将姐妹分类单元置于同一级序,必要时将并系群与其后裔类群置于同一级序,而姐妹群则可能被置于不同的级序。采用近亲单元和准近亲单元分别作为无级序的单系群和并系群的标识,解决了将化石分类群融入现代生物分类系统的技术难题,可简化并有效地保持分类系统的稳定性。新方法使双壳纲完成从形态分类向准分支系统分类的转变,这代表着分类学未来发展的新趋势,而林奈式级序体系则为林奈系统今后的改革提供了新的范例。
The synopsis suprageneric classification of the Bivalvia for the upcoming revision of Bivalvia volumes of the Treatise on Invertebrate Paleontology,Part N has been published （Carter et al. , 2011）, and the introductory volume of the revised Bivalvia Treatise is coming to the press. Paleontologists, biologists and molecular biologists have made concerted efforts to fit fossils and extant bivalves into one and the same classificatory system. The new classification combines the phylogeny concept of evolutionary taxonomy with the rational kernel of cladistic method, but abandons the irrational classification principles of cladistics such as its refusal to accept paraphyletic groups, its principle of ob- ligatory dichotomy and its imperative for sister groups to have the same hierarchical rank. It gives full play to the advantages of the Linnaean system and patches up its shortcomings by adopting synapomorphies as the basis of grouping, by ranking of taxa for searching after phylogenetic relationships, and by adopting unranked plesions and paraple- sions for keeping the stability of taxonomic systems. This leads to the paracladistic approach and a comprehensive reclassification of the Bivalvia is taking shape as a consequence, differing substantially from the morphological classification of first edition of the Bivalvia Treatise. Paracladistic systematics reflects both ancestor-descendant relationships and recency of common ancestry, corresponds the branching points on a phylogenetic tree with times of apormorphy divergence, and gives consideration to both cladogenesis and anagenesis, including recency of common ancestry, the amount of evolutionary change and taxonomic diversity, when assigning taxonomic ranks. The new classification employs cladistic methods to distinguish plesiomorphies from apomorphies, to polarize characters by outgroup comparison, ontogeny, fossil evidence and stratigraphic sequence, to pay attention to distinguish between homoplasy and homology, to determine recency of common ancestry using the most compelling evidence from molecular and mor- phological phylogenetics, and then to evaluate these data in the context of stratigraphic order, to analyze character evolution in the Bivalvia by parsimony analysis, and to generate ancestor-descendant hypotheses and to build the phylogenetic tree. In constructing the classificatory system, the con-cept of a monophyletic group is favoured, but paraphyletic natural groups are also formally recognized and defined by the presence of specified apomorphies and by the absence of apomorphies that define their descendent clade or clades. Phylogenetic tree is used to construct the hierarchic frame- work, referring to cladogram methodology and corresponding ranks to the branching points of phylogenetic tree, so as to avoid subjectivity and arbitrariness in rank determination. Sister taxa are generally assigned the same Linnaean rank, also paraphyletic groups and their descendants while sister taxa would be assigned to the different ranks. In recent years, the study of Bivalvia phylogeny has made a series of significant progress. In order to more properly reflect phylogenetic relationships, and to mirror the latest interpretation of the cladistic evolutionary history of the Bivalvia, the new classification had to use up to 18 suprageneric categorical ranks and some unranked taxa or clade names; but only 6 suprageneric categorical ranks in the first edition of the Bivalvia Treatise. Evidently, the new classification is much more verbose and cumbersome to use, however, this is the cost we must pay for reflecting phylogenetic relationships. To solve this problem, in general, it is recommended to use a more simplified and condensed classification. All supraspecific bivalve taxa published in China （Fang et aZ. , 2009） are seriously treated and discussed in the revised Bivalvia Treatise, and the introduction of a large number of Chinese materials significantly improved the new classification of the Bivalvia. The paracladistic approach integrates the Linnaean system of classification with cladistic analyses and represents a new direction for the future development of taxonomy and for the neo-Linnaean nomenclature and hierarchy.
出处
《古生物学报》
CAS
CSCD
北大核心
2014年第1期16-32,共17页
Acta Palaeontologica Sinica
基金
现代古生物学和地层学国家重点实验室课题(No.123114)资助
