Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA.
Czech Academy of Sciences, Institute of Geology, Rozvojová 269, 165 00, Prague 6, Czech Republic; Institute of Geology and Palaeontology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic.
Arthropod Struct Dev. 2021 Jul;63:101059. doi: 10.1016/j.asd.2021.101059. Epub 2021 May 22.
Trilobites represent a model for 'evo-devo' studies in fossil euarthropods, owing to a rare developmental trait: the biomineralization of the dorsal exoskeleton soon after hatching. Many fossilized trilobite ontogenies thus feature early stages - the protaspides - characterized by non-articulated, calcified dorsal exoskeletons. The recent discovery of a protaspid-like fossil occurring with aglaspidid remains in Middle Ordovician strata of Siberia has been interpreted as evidence for the presence of protaspides in these distant relatives of trilobites. In this contribution, we demonstrate that this Siberian protaspis actually belongs to the asaphid trilobite Isotelus (or a related taxon), a genus likely present in the same bed. We conclude that protaspid larvae still represent a developmental trait unique to Trilobita.
三叶虫是化石节肢动物“演化发育”研究的典范，这要归因于其罕见的发育特征：在孵化后不久，背部外骨骼就开始生物矿化。因此，许多已灭绝的三叶虫的个体发育史都具有早期阶段——原头节，其特征是非关节、钙化的背部外骨骼。最近在西伯利亚中奥陶统地层中发现了一个与桨足类化石一起保存的原头节样化石，这被解释为这些三叶虫远亲存在原头节的证据。在本研究中，我们证明了这种西伯利亚原头节实际上属于三叶虫中的栉虫（或相关的分类单元），这个属很可能存在于同一地层中。我们的结论是，原头节幼虫仍然是三叶虫特有的发育特征。
