Trinucleoids have been considered as a superfamily of the Order Asaphida, based on: a pre-occipital glabellar tubercle, a cephalic median suture in most ancestral forms, and the presence of broadly similar globular protaspid larvae in the life cycle. Recent discoveries cast doubts on the monophyly of the two last characters. This study provides a phylogenetic analysis whose main purpose is to test the affiliation of trinucleoids. The topology of the strict consensus tree obtained indicates that trinucleoids share a more recent common ancestor with members of the Order Ptychopariida than they do with any asaphid. The stratigraphically higher and most derived trinucleoids are well defined and easy to recognize. Their basal representatives can also be identified with confidence, in spite of substantial variation in the diagnostic characters of the group. These early trinucleoids are similar enough to the typical basal ‘ptychopariid’ bauplan to suggest ancestry within that diffuse and poorly defined trilobite order. Indeed, Ptychopariida is presently regarded as being paraphyletic. We consider that raising trinucleids to ordinal status, by proposing the Order Trinucleida, will make it easier to decipher higher level relationships among trilobites. This action, sustained by improved morphological and ontogenetic information of Cambro-Ordovician trilobites, reveals convergences of the three characters that have been used to support the inclusion of trinucleids within Asaphida. Based on this new information, we propose six distinct morphotypes of commutavi protaspis and, as a probable sensorial organ, that the cephalic axial tubercle migration might be caused by an increase in the height of the glabella and thus may not bear an important systematic signal. Moreover, the tree topology provided herein offers a preliminary overview of evolution within the order. Alsataspididae and Raphiophoridae are paraphyletic, suggesting that more investigation is needed to define them clearly. Dionidae appears to be more closely related to Raphiophoridae than to Trinucleidae, suggesting that the character state of ‘a perforated fringe’ evolved more than once.

三核苷酸被认为是甲状纲的超家族，其依据是：枕前前结节结节，大多数祖先形式的头侧正中缝合线，以及生命周期中广泛存在相似的球状鹰嘴幼虫。最近的发现使人们对最后两个字符的单调性产生了怀疑。这项研究提供了系统发育分析，其主要目的是测试三核苷酸的隶属关系。所获得的严格共有树的拓扑结构表明，三核苷酸与鼠疫目（Ptychopariida）的成员相比具有更近的共同祖先，而不是与任何蚜虫一样。地层学上较高且衍生最多的三核苷定义明确，易于识别。他们的基层代表也可以自信地找到，尽管该组的诊断特征存在很大差异。这些早期的三核苷与典型的基底“ ptychopariid”鲍普兰足够相似，以表明在该扩散且定义不清的三叶虫顺序内的祖先。实际上，目前认为鼠疫杆菌是共生的。我们认为，通过提出三核纲（Order Trinucleida），将三核提升到序数状态将使解密三叶虫之间更高层次的关系变得更加容易。通过改善坎布罗-奥陶纪三叶虫的形态学信息和本体信息来维持这一作用，揭示了已被用来支持三核内含三核的三个字符的融合。根据这一新信息，我们提出了六个易变型的通勤型，作为可能的感觉器官，头部轴向结节的迁移可能是由于间质的高度增加引起的，因此可能没有重要的系统信号。此外，本文提供的树形拓扑结构提供了该顺序内进化的初步概述。Alsataspididae和Raphiophoridae是共生的，这表明需要更多的研究来明确定义它们。Dionidae与Raphiophoridae的关系似乎比与Trinucleidae的关系更紧密，这表明“穿孔边缘”的性状进化了一次以上。建议需要进行更多调查以明确定义它们。Dionidae与Raphiophoridae的关系似乎比与Trinucleidae的关系更紧密，这表明“穿孔边缘”的性状进化了一次以上。建议需要更多调查以明确定义它们。Dionidae与Raphiophoridae的关系似乎比与Trinucleidae的关系更紧密，这表明“穿孔边缘”的性状进化了一次以上。