Li Huarui, Dai Tao, Chen Yanlong, Xue Chunling, Strotz Luke C
State Key Laboratory of Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an 710069, China.
College of Chemical and Environmental Engineering, Hanjiang Normal University, Shiyan 442000, China.
Life (Basel). 2024 Dec 31;15(1):38. doi: 10.3390/life15010038.
The temporal range of eodiscids and agnostoid arthropods overlaps with several early Paleozoic geological events of evolutionary significance. However, the responses of agnostids to these events and how the perturbations associated with them (both abiotic and/or biotic) may have impacted agnostids remain uncertain. To address this uncertainty, we employ geometric morphometrics to reconstruct morphospace occupation for agnostids, thereby elucidating their evolutionary response to geological events during the early Paleozoic. The results indicate that maximum morphospace occupation was reached by Cambrian Series 2 and then declined soon thereafter. Subsequent reductions in agnostid morphospace occupation coincide not only with significant abiotic changes and associated extinction events, such as the Botoman-Toyonian Extinctions (BTEs), the Redlichiid-Olenellid Extinction Carbon Isotope Excursion (ROECE), the Drumian Carbon Isotope Excursion (DICE), and the Steptoean Positive Carbon Isotope Excursion event (SPICE), but also with major evolutionary episodes, such as the Great Ordovician Biodiversification Event (GOBE). These repeated and periodic declines in agnostid morphological diversity following Cambrian Series 2 suggest that the extinction of agnostids reflects the culmination of an episodic reduction in morphological occupancy for agnostids rather than a singular, sudden event. Accordingly, it cannot be tied to a single cause, either abiotic or biotic.
艾氏虫类和疑源节肢动物的时间范围与几个具有进化意义的早古生代地质事件重叠。然而，疑源类对这些事件的反应以及与之相关的扰动（包括非生物和/或生物扰动）如何影响疑源类仍然不确定。为了解决这一不确定性，我们采用几何形态测量学来重建疑源类的形态空间占据情况，从而阐明它们在早古生代对地质事件的进化反应。结果表明，寒武纪第2统时疑源类达到了最大的形态空间占据，此后不久便开始下降。疑源类形态空间占据的后续减少不仅与重大的非生物变化及相关的灭绝事件同时发生，如波托曼阶—托依阶灭绝事件（BTEs）、莱德利基虫—小油栉虫灭绝碳同位素偏移事件（ROECE）、德鲁米安阶碳同位素偏移事件（DICE）以及斯特普托阶正碳同位素偏移事件（SPICE），还与主要的进化事件同时发生，如奥陶纪生物大辐射事件（GOBE）。寒武纪第2统之后疑源类形态多样性的这些反复和周期性下降表明，疑源类的灭绝反映了疑源类形态占据的阶段性减少的顶点，而不是单一的突然事件。因此，它不能归因于单一原因，无论是非生物原因还是生物原因。
