Buatois Luis A, Mángano Maria G, Olea Ricardo A, Wilson Mark A
Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E2;
Eastern Energy Resources Science Center, US Geological Survey, Reston, VA 20192;
Proc Natl Acad Sci U S A. 2016 Jun 21;113(25):6945-8. doi: 10.1073/pnas.1523087113. Epub 2016 May 31.
Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal-substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation.
寒武纪大爆发（CE）与奥陶纪生物大辐射事件（GOBE）之间的对比早已为人所知。虽然绝大多数动物形态结构是寒武纪大爆发的结果，但奥陶纪生物大辐射期间的分类学增加表现在较低的分类学水平上。评估这两次进化事件导致的遗迹多样性和遗迹差异的变化，可能有助于揭示这两次辐射的动态过程。早寒武世（第1和2统）软底群落的遗迹多样性和遗迹差异显著增加。与生物扰动结构的这种进化爆发形成对比的是，已知的寒武纪生物侵蚀结构很少。在寒武纪中晚期多样性稳定期之后，软底群落的遗迹多样性在奥陶纪期间在浅海和深海环境中都持续增加。奥陶纪生物扰动多样性的这种增加并没有伴随着遗迹差异像寒武纪大爆发期间那样同样显著的增加。然而，在奥陶纪生物大辐射期间，硬底群落有显著不同，遗迹多样性和遗迹差异都有所增加。大型生物侵蚀的创新明显落后于未固结沉积物中动物与基质的相互作用。这种进化解耦的根本原因尚不清楚，但可能涉及三个相互关联的因素：（i）奥陶纪中晚期生物侵蚀可用硬底质的增加，（ii）捕食增加，以及（iii）与生物扰动相比，生物侵蚀对能量的需求更高。
