Precambrian animal life: Taphonomy of phosphatized metazoan embryos from southwest China
Precambrian animal life: Taphonomy of phosphatized metazoan embryos from southwest China
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DOI：
10.1080/00241160510013187
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发表时间：
2005-06
期刊：
影响因子：
1.5
通讯作者：
D. Stephen;B. David;Jun‐yuan Chen;O. Paola;Gao Feng;Lin Chia‐wei
中科院分区：
文献类型：
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作者：
D. Stephen;B. David;Jun‐yuan Chen;O. Paola;Gao Feng;Lin Chia‐wei
新元古代陡山沱组的磷酸盐化化石为后生动物的早期演化提供了宝贵的信息，但这些壮观化石的保存情况尚未完全了解。本研究通过对陡山沱组磷酸盐化后生动物胚胎进行详细的埋藏学分析，试图解决这一问题。对陡山沱组瓮安磷块岩段65个薄片共206个胚胎进行了研究，并对其磷酸盐化前的衰变程度进行了估算。从这次检查产生的数据揭示了一个强大的埋藏偏向早期（2-细胞和4-细胞）的卵裂阶段，往往保存完好，并远离后期（8-细胞和16-细胞）的卵裂阶段，往往表现出轻微到强烈的有机衰变水平的证据。此外，这些胚胎的自然丰度往往随着卵裂阶段的进展而减少，并且在本研究中没有发现更高级（超过16个细胞）卵裂阶段或最终成体形式的证据。对这种埋藏学偏向早期卵裂阶段的一个可能的解释是，后期卵裂阶段和成体形式在物理上更脆弱，使它们在埋葬和改造过程中更容易受损，从而更快地腐烂。这些胚胎的壮观保存可能是由于它们可能在富含磷酸盐的蛋黄中的内部富集，这将导致它们的内部溶解磷酸盐水平达到临界水平，只有极微小的有机衰变，从而加速磷酸化。如果磷酸盐的内部来源确实在这些胚胎的磷酸盐化中发挥了作用，那么与其他磷酸盐化化石相比，它可以解释这些岩石中的多产丰度，并表明缺乏这种内部磷酸盐来源的后生动物可能更难以保存。陡山沱组的磷质化石，因此，提供了一个不可或缺的，但限制，窗口新元古代生活和后生动物的起源。
Phosphatized fossils from the Neoproterozoic Doushantuo Formation have provided valuable insight into the early evolution of metazoans, but the preservation of these spectacular fossils is not yet fully understood. This research begins to address this issue by performing a detailed specimen-based taphonomic analysis of the Doushantuo Formation phosphatized metazoan embryos. A total of 206 embryos in 65 thin sections from the Weng'an Phosphorite Member of the Doushantuo Formation were examined and their levels of pre-phosphatization decay estimated. The data produced from this examination reveal a strong taphonomic bias toward earlier (2-cell and 4-cell) cleavage stages, which tend to be well-preserved, and away from later (8-cell and 16-cell) cleavage stages, which tend to exhibit evidence for slight to intense levels of organic decay. In addition, the natural abundances of these embryos tend to decrease with advancement in cleavage stage, and no evidence of more advanced (beyond 16-cell) cleavage stages or eventual adult forms were found in this study. One possible explanation for this taphonomic bias toward early cleavage stages is that later cleavage stages and adult forms were more physically delicate, allowing them to be more easily damaged during burial and reworking, allowing for more rapid decay. The spectacular preservation of these embryos was probably aided by their likely internal enrichment in phosphate-rich yolk, which would have caused their internal dissolved phosphate levels to reach critical levels with only miniscule organic decay, thereby hastening phosphatization. If internal sources of phosphate did indeed play a role in the phosphatization of these embryos, it may explain their prolific abundance in these rocks compared to other phosphatized fossils as well as indicating that metazoans lacking such internal phosphate sources were likely much more difficult to preserve. The phosphatic fossils of the Doushantuo Formation, therefore, provide an indispensable, yet restricted, window into Neoproterozoic life and metazoan origins.