Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, Uppsala, 752 36, Sweden.
Commun Biol. 2022 Nov 4;5(1):1177. doi: 10.1038/s42003-022-04146-6.
Trilobites are an iconic Paleozoic group of biomineralizing marine euarthropods that appear abruptly in the fossil record (c. 521 million years ago) during the Cambrian 'explosion'. This sudden appearance has proven controversial ever since Darwin puzzled over the lack of pre-trilobitic fossils in the Origin of Species, and it has generally been assumed that trilobites must have an unobserved cryptic evolutionary history reaching back into the Precambrian. Here we review the assumptions behind this model, and suggest that a cryptic history creates significant difficulties, including the invocation of rampant convergent evolution of biomineralized structures and the abandonment of the synapomorphies uniting the clade. We show that a vicariance explanation for early Cambrian trilobite palaeobiogeographic patterns is inconsistent with factors controlling extant marine invertebrate distributions, including the increasingly-recognized importance of long-distance dispersal. We suggest that survivorship bias may explain the initial rapid diversification of trilobites, and conclude that the group's appearance at c. 521 Ma closely reflects their evolutionary origins.
三叶虫是一种标志性的古生代生物矿化海洋节肢动物，它们在寒武纪“大爆发”期间（约 5.21 亿年前）突然出现在化石记录中。自从达尔文在《物种起源》中对缺少前三叶虫化石感到困惑以来，这种突然出现一直存在争议，人们普遍认为三叶虫一定有一个未被观察到的隐生进化历史，可以追溯到前寒武纪。在这里，我们回顾了这一模型背后的假设，并认为隐生历史会带来重大困难，包括生物矿化结构的猖獗趋同进化的推断以及联合该进化枝的同源特征的放弃。我们表明，对早寒武世三叶虫古生物地理模式的隔离解释与控制现存海洋无脊椎动物分布的因素不一致，包括远距离扩散的重要性日益增加。我们认为，幸存偏差可能解释了三叶虫最初的快速多样化，并且得出结论，该群体在大约 5.21 亿年前的出现很好地反映了它们的进化起源。
