LoDuca S T, Bykova N, Wu M, Xiao S, Zhao Y
Department of Geography and Geology, Eastern Michigan University, Ypsilanti, MI, USA.
Department of Geosciences, Virginia Tech, Blacksburg, VA, USA.
Geobiology. 2017 Jul;15(4):588-616. doi: 10.1111/gbi.12244. Epub 2017 Jun 12.
Non-calcified marine macroalgae ("seaweeds") play a variety of key roles in the modern Earth system, and it is likely that they were also important players in the geological past, particularly during critical transitions such as the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE). To investigate the morphology and ecology of seaweeds spanning the time frame from the CE through the GOBE, a carefully vetted database was constructed that includes taxonomic and morphometric information for non-calcified macroalgae from 69 fossil deposits. Analysis of the database shows a pattern of seaweed history that can be explained in terms of two floras: the Cambrian Flora and the Ordovician Flora. The Cambrian Flora was dominated by rather simple morphogroups, whereas the Ordovician Flora, which replaced the Cambrian Flora in the Ordovician and extended through the Silurian, mainly comprised comparatively complex morphogroups. In addition to morphogroup representation, the two floras show marked differences in taxonomic composition, morphospace occupation, functional-form group representation, and life habit, thereby pointing to significant morphological and ecological changes for seaweeds roughly concomitant with the GOBE and the transition from the Cambrian to Paleozoic Evolutionary Faunas. Macroalgal changes of a similar nature and magnitude, however, are not evident in concert with the CE, as the Cambrian Flora consists largely of forms established during the Ediacaran. The cause of such a lag in macroalgal morphological diversification remains unclear, but an intriguing possibility is that it signals a previously unknown difference between the CE and GOBE with regard to the introduction of novel grazing pressures. The consequences of the establishment of the Ordovician Flora for shallow marine ecosystems and Earth system dynamics remain to be explored in detail but could have been multifaceted and potentially include impacts on the global carbon cycle.
非钙化海洋大型藻类（“海藻”）在现代地球系统中发挥着多种关键作用，它们在地质历史时期可能也很重要，尤其是在寒武纪大爆发（CE）和奥陶纪生物大辐射事件（GOBE）等关键转变时期。为了研究从寒武纪大爆发到奥陶纪生物大辐射事件期间海藻的形态和生态，构建了一个经过仔细审核的数据库，其中包含来自69个化石矿床的非钙化大型藻类的分类和形态测量信息。对该数据库的分析显示出海藻历史的一种模式，可以用两个植物区系来解释：寒武纪植物区系和奥陶纪植物区系。寒武纪植物区系以相当简单的形态类群为主，而奥陶纪植物区系在奥陶纪取代了寒武纪植物区系并延续至志留纪，主要由相对复杂的形态类群组成。除了形态类群的表现外，这两个植物区系在分类组成、形态空间占据、功能形态类群表现和生活习性方面也存在显著差异，从而表明海藻在形态和生态上发生了重大变化，大致与奥陶纪生物大辐射事件以及从寒武纪到古生代演化动物群的转变同时发生。然而，与寒武纪大爆发同时期，类似性质和规模的大型藻类变化并不明显，因为寒武纪植物区系主要由埃迪卡拉纪时期形成的形态组成。大型藻类形态多样化出现这种滞后的原因尚不清楚，但一种有趣的可能性是，它表明在引入新的放牧压力方面，寒武纪大爆发和奥陶纪生物大辐射事件之间存在前所未知的差异。奥陶纪植物区系的建立对浅海生态系统和地球系统动态的影响仍有待详细探索，但可能是多方面的，并且可能包括对全球碳循环的影响。
