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.

长期以来，诸多文德纪（Vendian，新元古代末期）的实体化石被视作节肢动物或类节肢动物。部分寒武纪"奇异型生物"亦被关联至节肢动物类群。然而，这些演化关系在传统林奈分类系统（Linnean systematics）中难以得到清晰阐释。本文针对7个文德纪"类节肢动物"分类群，与21个具代表性的寒武纪节肢动物、叶足动物门（Lobopoda）及奇异型生物开展形态学支序分类分析。本次研究同时纳入了以下类群：4种显生宙后期的节肢动物，分别为1种海蜘蛛类（Pycnogonida）、1种单尾类（Monura），以及存疑的奇雷尔虫（Cheloniellon）与节肋虫（Arthropleura）；5种现生缓步动物（Tardigrada，俗称水熊虫）；2种现生动吻动物（Kinorhyncha）；以及1种现生曳鳃动物（Priapulida）、1种多足类（Myriapoda）、1种海蜘蛛类及1种有爪动物（Onychophora）。分析结果支持节肢动物的单系性，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，应归入节肢动物门下。具单枝型附肢的节肢动物类群间的演化关系尚未得到充分解析，且该类群并非单系群。具双枝型附肢的节肢动物则构成单系支系，可进一步划分为甲壳形类群（crustaceanomorph）与包含三叶虫（Trilobita）的蛛形形类群（arachnomorph）。多数文德纪类节肢动物化石位于节肢动物干群中，形成文德形类（Vendiamorpha）与斯普里格虫科（Sprigginidae）两个支系。叶足动物门为一单系支系，包含三个分支：缓步动物、有爪动物及海洋叶足类。本文为本次研究识别的主要支系提出了一套无等级划分的分类方案。现有证据并无充分理由支持"本次纳入分析的文德纪生物并非后生动物（Metazoa）"这一假说。