The group Vertebrata is currently placed as a subphylum in the phylum Chordata, together with two other subphyla, Cephalochordata (lancelets) and Urochordata (ascidians). The past three decades, have seen extraordinary advances in zoological taxonomy and the time is now ripe for reassessing whether the subphylum position is truly appropriate for vertebrates, particularly in light of recent advances in molecular phylogeny, comparative genomics, and evolutionary developmental biology. Four lines of current research are discussed here. First, molecular phylogeny has demonstrated that Deuterostomia comprises Ambulacraria (Echinodermata and Hemichordata) and Chordata (Cephalochordata, Urochordata, and Vertebrata), each clade being recognized as a mutually comparable phylum. Second, comparative genomic studies show that vertebrates alone have experienced two rounds of whole-genome duplication, which makes the composition of their gene family unique. Third, comparative gene-expression profiling of vertebrate embryos favors an hourglass pattern of development, the most conserved stage of which is recognized as a phylotypic period characterized by the establishment of a body plan definitively associated with a phylum. This mid-embryonic conservation is supported robustly in vertebrates, but only weakly in chordates. Fourth, certain complex patterns of body plan formation (especially of the head, pharynx, and somites) are recognized throughout the vertebrates, but not in any other animal groups. For these reasons, we suggest that it is more appropriate to recognize vertebrates as an independent phylum, not as a subphylum of the phylum Chordata.

中文翻译：

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椎骨门：一个生态学认识的案例

脊椎动物群目前与其他两个亚目：头足目（矛头）和Urochordata（海鞘）一起作为Chordata门的一个亚门放置。在过去的三十年中，在动物学分类学方面取得了非凡的进步，现在重新评估亚门的位置是否真正适合脊椎动物的时机已经成熟，尤其是鉴于分子系统发育，比较基因组学和进化发育生物学的最新进展。本文讨论了当前的四项研究。首先，分子系统发育学证明了子宫口畸形包括无腕动物（棘皮动物和半翅目）和鸡眼（Cephalochordata，Urochordata和Vertebrata），每个进化枝都被认为是相互可比的门。第二，比较基因组研究表明，仅脊椎动物就经历了两轮全基因组重复，这使得它们的基因家族组成独特。第三，脊椎动物胚胎的比较基因表达图谱倾向于沙漏状的发育模式，其最保守的阶段被认为是系统性发育阶段，其特征是建立了与系统性发育有关的身体计划。胚胎中期这种保守的保护在脊椎动物中得到有力的支持，而在脊索动物中则只有很少的支持。第四，在整个脊椎动物中都可以识别出某些复杂的身体计划形成模式（尤其是头部，咽部和体节），但在其他任何动物组中却没有。由于这些原因，我们建议将脊椎动物识别为独立的门是更合适的，