Data from: Phylogenetic hypotheses of the relationships of arthropods to Precambrian and Cambrian problematic fossil taxa

A number of Vendian (latest Precambrian) body fossils have traditionally been considered arthropods or arthropodlike organisms. Several Cambrian "weird wonders" have also been linked with the arthropods. However, these relationships are difficult to express in traditional Linnean systematics. I present a morphological cladistic analysis of seven Vendian "arthropodlike" taxa compared with 21 representative Cambrian arthropods, lobopods, and weird wonders. Four arthropods from the later Phanerozoic (a pycnogonid, a monuran, and the problematic Cheloniellon and Arthropleura), five extant tardigrades, two extant kinorhynchs, and an extant priapulid, myriapod, pycnogonid, and onychophoran are also included. Monophyly of the Arthropoda is supported, but the anomalocarids and their relatives (Anomalopoda) fall out very close to the base of the traditional Arthropoda and should be included within it. The relationships among arthropods with uniramous appendages are not well resolved, but the group does not appear to be monophyletic. The biramous arthropods do form a clade and are divided into a crustaceanomorph clade and an arachnomorph clade that includes the trilobites. Most Vendian arthropodlike fossils form two clades, the Vendiamorpha and the Sprigginidae, in the arthropod stem group. The Lobopoda is a monophyletic clade with three branches: tardigrades, onychophorans, and marine lobopods. An unranked taxonomic scheme is proposed for the major clades identified here. There is no compelling reason to accept the hypothesis that the Vendian organisms included here are not metazoans.

传统上，诸多文德纪（Vendian，最新前寒武纪）的实体化石被认定为节肢动物（Arthropoda）或类节肢动物生物。另有多种寒武纪“奇异型生物”也被关联至节肢动物类群范畴。然而，这类演化关联在传统林奈分类系统（Linnean systematics）中难以清晰阐释。本研究针对7个文德纪“类节肢动物”类群，与21种代表性寒武纪节肢动物、叶足动物（Lobopoda）及奇异型生物开展形态学分支系统学对比分析。本研究同时纳入了4种晚显生宙（Phanerozoic）节肢动物：1种海蜘蛛类（pycnogonid）、1种原尾虫（monuran），以及存疑的切海三叶虫（Cheloniellon）和节肋虫（Arthropleura）；另有5种现生缓步动物（tardigrades）、2种现生动吻动物（kinorhynchs），以及1种现生曳鳃动物（priapulid）、多足类（myriapod）、海蜘蛛类及有爪动物（onychophoran）。研究结果显示，节肢动物门的单系性得到支持，但奇虾类及其近缘类群（Anomalopoda）的分支位置紧邻传统节肢动物的基部类群，应被纳入节肢动物门范畴。具单枝型附肢的节肢动物之间的演化关系尚未得到充分解析，且该类群并非单系群；而具双枝型附肢的节肢动物则构成一个单系类群，可进一步划分为甲壳形类群分支（crustaceanomorph clade）与包含三叶虫在内的蛛形形类群分支（arachnomorph clade）。多数文德纪类节肢动物化石在节肢动物干群中构成两个单系类群：文德虫形类（Vendiamorpha）与斯普里格虫科（Sprigginidae）。叶足动物门为单系类群，包含缓步动物、有爪动物与海洋叶足动物三个演化支。本研究针对本次分析鉴定出的主要类群，提出了一套无等级划分的分类系统。并无充分证据支持“本次研究纳入的文德纪生物并非后生动物（metazoans）”这一假说。