The world may need to start thinking differently about plants, according to a 报告 在杂志上 科学 by researchers who took a fresh look at spore-like microfossils with characteristics that challenge our conventional understanding about the evolution of land plants.
Found in rock samples retrieved in Australia more than 60 years ago, the microfossils dating to the Lower Ordovician Period, 大约在4.8亿年前, fill an approximately 25-million-year gap in knowledge by reconciling the molecular clock—or pace of evolution—with the fossil spore record—the physical evidence of early plant life gathered by scientists over the years.
古植物学家保罗·斯特罗瑟说
This reconciliation supports an evolutionary-developmental model connecting plant origins to freshwater green algae, 或者绿藻, said 电子游戏软件 paleobotanist 保罗斯特罗瑟, 新报告的合著者之一. The “evo-devo” model posits a more nuanced understanding of plant evolution over time, from simple cell division to initial embryonic stages, rather than large jumps from one species to another.
“We found a mix of fossils linking older, more problematic spore-like microfossils with younger spores that are clearly derived from land plants,斯特罗瑟说. “This helps to bring the fossil spore record into alignment with molecular clock dates if we consider the origin of land plants as a long-term process involving the evolution of embryonic development.”
The fossil record preserves direct evidence of the evolutionary assembly of the plant regulatory and developmental genome, 斯特罗瑟说. This process starts with the evolution of the plant spore and leads to the origin of plant tissues, 器官, 最后是宏观的, complete plants—perhaps somewhat akin to mosses living today.
“When we consider spores as an important component of the evolution of land plants, there is no longer a gap in the fossil record between molecular dating and fossil recovery,斯特罗瑟说. 没有这个差距, “we have a much clearer picture of a whole new evolutionary step: from simple cellularity to complex multicellularity.”
结果是, researchers and the public may need to re-think how they view the origin of terrestrial plants—that pivotal advance of life from water to land, 斯特罗瑟说.
“We need to move away from thinking of the origin of land plants as a singularity in time, and instead integrate the fossil record into an evo-devo model of genome assembly across millions of years during the Paleozoic Era—specifically between the Cambrian and Devonian divisions within that era,斯特罗瑟说. “This requires serious re-interpretation of problematic fossils that have previously been interpreted as fungi, 不是植物.”
Strother and co-author Clinton Foster, of the Australian National University, set out to simply describe an assemblage of spore-like microfossils from a deposit dating to the Early Ordovician age—大约在4.8亿年前. This material fills in a gap of approximately 25 million years in the fossil spore record, linking well-accepted younger plant spores to older more problematic forms, 斯特罗瑟说.
Strother and Foster examined populations of fossil spores extracted from a rock core drilled in 1958 in northern Western Australia. These microfossils are composed of highly resistant organic compounds in their cell walls that can structurally survive burial and lithification. 他们在电子游戏软件学习, and at the ANU’s 电子游戏正规平台 School of Earth 科学s, with standard optical light microscopy.
“We use fossil spores extracted from rock drill cores to construct an evolutionary history of plants going back in time to the very origin of plants from their algal ancestors,斯特罗瑟说. “We have independent age control on these rock samples, so we study evolution by looking at changes in the kinds of spores that occur over time.”
Molecular biologists also look at evolutionary history through time by using genes from living plants to estimate the timing of plant origins using “molecular clocks”—a measurement of evolutionary divergence based on the average rate during which mutations accumulate in a species’ genome.
然而, 存在巨大的差异, 长达数千万年, between direct fossil data and molecular clock dates, 斯特罗瑟说. 除了, there are similar time gaps between the oldest spores and when actual whole plants first occur.
These gaps resulted in hypotheses about a “missing fossil record” of the earliest land plants, 斯特罗瑟说.
“Our work seeks to resolve some of these questions by integrating the fossil spore record into an evolutionary developmental model of plant origins from algal ancestors,斯特罗瑟说.
Ed Hayward | University Communications | September 2021