Data from: Ontogeny of the Furongian (late Cambrian) trilobite Proceratopyge cf. P. Lata Whitehouse from northern Victoria Land, Antarctica, and the evolution of metamorphosis in trilobites

There were multiple origins of metamorphosis-undergoing protaspides in trilobite evolution: within the superfamilies Remopleuridioidea, Trinucleoidea, and within the Order Asaphida. Recent studies have revealed that the protaspides of the Cambrian representatives of the Remopleuridioidea and the Trinucleoidea did not undergo metamorphosis. However, ontogeny of the Cambrian members of the Order Asaphida has remained unknown. This study documents the ontogeny of the Furongian asaphoidean ceratopygid trilobite, Proceratopyge cf. P. lata Whitehouse, from northern Victoria Land, Antarctica. Two stages for the protaspid phase, five developmental stages for the post-protaspid cranidia, and ten stages for the post-protaspid pygidia have been identified. Interestingly, the protaspis directly developed into a meraspis without metamorphosis. A new cladistic analysis resulted in a single most parsimonious tree, according to which the presence of the bulbous commutavi protaspis turns out to be a synapomorphy for Asaphidae + Cyclopygoidea, not a synapomorphy for the Order Asaphida as previously suggested. In addition, it is inferred that there was convergent evolution of indirectly-developing commutavi protaspides during the Furongian and Early Ordovician. Metamorphosis-entailing planktonic larvae evolved in many different metazoan lineages near the Cambrian–Ordovician transition, due to the escalating ecological pressure of the Great Ordovician Biodiversification Event. Since the bulbous commutavi protaspid morphology is thought to be an adaptation for a planktonic life mode, the convergent evolution of the indirect development in the three trilobite lineages at this period might have been a result of adaptation to the early phase of the Great Ordovician Biodiversification Event.

三叶虫演化中，具备变态发育的原幼虫（protaspides）存在多起源路径：分别见于弯线虫总科（Remopleuridioidea）、三瘤虫总科（Trinucleoidea）以及蚜头虫目（Asaphida）内部。近期研究显示，弯线虫总科与三瘤虫总科的寒武纪代表类群的原幼虫并未经历变态发育。然而，蚜头虫目寒武纪成员的个体发育（ontogeny）至今仍不明确。本研究记述了采自南极洲维多利亚地北部的芙蓉世（Furongian）蚜头虫总科角尾虫科原角尾虫（Proceratopyge cf. P. lata Whitehouse）的个体发育序列。研究共识别出原幼虫期的2个发育阶段、后原幼虫期头甲（cranidia）的5个发育阶段，以及后原幼虫期尾甲（pygidia）的10个发育阶段。值得注意的是，该类群的原幼虫直接发育为分节幼虫期（meraspis），未经历变态发育。全新的分支系统学分析（cladistic analysis）得到唯一一棵最简约树（most parsimonious tree），结果显示球状commutavi型原幼虫（bulbous commutavi protaspis）实为蚜头虫科（Asaphidae）与圆尾虫总科（Cyclopygoidea）的共有衍征（synapomorphy），而非此前所提出的蚜头虫目的共有衍征。此外，研究推断芙蓉世至早奥陶世期间，具间接发育的commutavi型原幼虫存在趋同演化（convergent evolution）现象。在寒武纪-奥陶纪过渡时期，受大奥陶纪生物多样性事件（Great Ordovician Biodiversification Event）不断加剧的生态压力驱动，营浮游生活的变态发育幼虫在多个后生动物（metazoan）类群中独立演化。鉴于球状commutavi型原幼虫的形态被认为是适应浮游生活的特征，这一时期三叶虫三个演化支系间接发育的趋同演化，可能是对大奥陶纪生物多样性事件早期阶段的适应结果。