QUESTIONING THE EVIDENCE OF ORGANIC COMPOUNDS CALLED SPONGE BIOMARKERS
QUESTIONING THE EVIDENCE OF ORGANIC COMPOUNDS CALLED SPONGE BIOMARKERS
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DOI：
10.1111/pala.12030
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发表时间：
2013-09-01
期刊：
影响因子：
2.6
通讯作者：
Antcliffe, Jonathan B.
中科院分区：
文献类型：
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作者：
Antcliffe, Jonathan B.
在阿曼的前寒武纪Huqf超群中发现的有机化合物24-异丙基胆甾烷的浓度升高可能提供了已知最古老的海绵化石。这一证据对于正确平衡地理解动物的起源至关重要。几种不同的浮游植物（浮游藻类纲，Chromaveolata中的层藻纲的一部分）藻类也能够产生这些确切的化合物，并且可能在很久以前就已经这样做了。据报道，现代海藻也能产生与海绵标记物在组成上相同的结构异构体;它们大量地这样做。此外，24-异丙基胆甾烷可以通过藻类大量产生的化合物的成岩变化来产生。也有可能是在从地下层提取这些化合物时取芯时使用的石油衍生润滑油造成的污染影响了数据。所有可能产生这种化合物的灭绝生物都无法被现代有机化学家分析，并且不能从海绵标记物的可能生产者名单中排除。关于这些古老化合物的地层年代也有很大的不确定性。虽然这些化合物被广泛报道为约751 Ma，但它们的年龄小于645 Ma。这些化合物似乎更可能代表了藻类生物化学演化的时间时，藻类埋藏发生了大量的众所周知的同时代藻类化石，但没有海绵化石。大型藻类生物量可能已经下降，在农业革命的基础上的寒武纪时期由于后生动物的加工，占这些海绵标志物在中生代沉积物中的相对稀缺，之后的时间海绵骨针和身体化石变得明显。
Elevated concentrations of an organic compound, 24-isopropylcholestane, found in the Precambrian Huqf Supergroup of Oman may provide the oldest known sponge fossil'. This evidence is of critical importance for a properly balanced understanding of the origin of animals. Several different pelagophyte (Class Pelagophyceae part of the Stramenopiles within the Chromaveolata) algae are also capable of producing these exact compounds, and may similarly have done so in deep time. Modern marine algae are also reported to produce structural isomers that are compositionally identical to the sponge marker; they do this in copious quantities. Further, 24-isopropylcholestane can be produced by diagenetic alteration of compounds produced in large quantities by algae. It is also possible that contamination by petroleum derived lubricating oil used when coring while extracting these compounds from subsurface layers, has affected the data. All extinct organisms that may have produced this compounds are unavailable for analysis by the modern organic chemist and cannot be eliminated from the list of possible producers of the sponge marker. There are also significant uncertainties regarding the dating of the strata from which these ancient compounds are found. Although the compounds are widely reported as c.751Ma, they are younger than 645Ma. It seems more likely that these compounds represent algal biochemical evolution at a time when algal burial occurred in great quantity with well known coeval algal fossils but no sponge fossils. The macroalgal biomass may have declined during the agronomic revolution at the base of the Cambrian Period owing to processing by metazoans, accounting for the comparative scarcity of these sponge markers in Phanerozoic sediments, after which time sponge spicules and body fossils become evident.