How green was Cooksonia?: The importance of size in understanding the early evolution of physiology in the vascular plant lineage
How green was Cooksonia?: The importance of size in understanding the early evolution of physiology in the vascular plant lineage
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DOI：
10.1666/0094-8373(2008)034
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发表时间：
2008-03-01
期刊：
影响因子：
2.7
通讯作者：
Boyce, C. Kevin
中科院分区：
文献类型：
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作者：
Boyce, C. Kevin
由于最早的类库克索尼亚陆生植物大型化石的碎片性保存，具有完整解剖保存和配子体记录的泥盆纪早期化石在维管植物的早期演化和世代交替方面往往受到更多的关注。然而，尽管存在保存缺陷，但考虑到整体轴的大小与细胞类型和大小的潜在范围，类库克索尼亚化石的可能生理学可能受到限制，因为它们缺乏器官分化，要求所有植物功能都由同一轴执行。一旦考虑到抗旱性、支撑力和运输功能，较小的化石没有足够的体积留给广泛的充气光合组织，因此争论生理上依赖于未保存的配子体。与许多苔藓一样，尽管孢子体干燥，轴向解剖更有可能确保孢子继续扩散，而不是提供光合作用的独立性。在志留纪和早泥盆世分类群中，通过与具有明显生理独立性的化石的尺寸比较、保存下来的解剖细节以及轴、孢子囊和孢子囊柄之间的尺寸相关性，支持了有关生理尺寸限制的假设。几个轴向宽度跨越一个数量级的类库克索属分类群块状化石——从必要的生理依赖到潜在的光合能力——为理解独立孢子体的进化和早期维管植物的系统发育关系提供了信息。
Because of the fragmentary preservation of the earliest Cooksonia-like terrestrial plant macrofossils, younger Devonian fossils with complete anatomical preservation and documented gametophytes often have received greater attention concerning the early evolution of vascular plants and the alternation of generations. Despite preservational deficits, however, possible physiologies of Cooksonia-like fossils can be constrained by considering the overall axis size in conjunction with the potential range of cell types and sizes, because their lack of organ differentiation requires that all plant functions be performed by the same axis. Once desiccation resistance, support, and transport functions are taken into account, smaller fossils do not have volume enough left over for an extensive aerated photosynthetic tissue, thus arguing for physiological dependence on an unpreserved gametophyte. As in many mosses, axial anatomy is more likely to have ensured continued spore dispersal despite desiccation of the sporophyte than to have provided photosynthetic independence. Suppositions concerning size constraints on physiology are supported by size comparisons with fossils of demonstrable physiological independence, by preserved anatomical detail, and by size correlations between axis, sporangia, and sporangial stalk in Silurian and Early Devonian taxa. Several Cooksonia-like taxa lump fossils with axial widths spanning over an order of magnitude-from necessary physiological dependence to potential photosynthetic competence-informing understanding of the evolution of an independent sporophyte and the phylogenetic relationships of early vascular plants.