DECAY AND PRESERVATION OF POLYCHAETES - TAPHONOMIC THRESHOLDS IN SOFT-BODIED ORGANISMS
DECAY AND PRESERVATION OF POLYCHAETES - TAPHONOMIC THRESHOLDS IN SOFT-BODIED ORGANISMS
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DOI：
10.1017/s0094837300012343
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发表时间：
1993-12-01
期刊：
影响因子：
2.7
通讯作者：
KEAR, AJ
中科院分区：
文献类型：
--
作者：
BRIGGS, DEG;KEAR, AJ
通过一系列实验研究了软组织降解的性质和控制因素（氧气、微生物种群、搅拌）。从形态变化、体重减轻和化学成分变化等方面监测了多毛藻的腐烂。多毛类包括一系列不同化学成分和保存潜力的组织类型：肌肉、角质层、刚毛和颚。无论在何种情况下，所有的肌肉都已经分解，角质层破裂导致的液体流失使尸体在20摄氏度的8天内缩小为二维。在大多数情况下，一些角质层，除了颚和刚毛，在30天后仍然存在。在完全消除氧气的情况下，挥发性较强的物质的衰变速度显著降低。胴体对水的渗透吸收程度和水pH值的变化取决于系统对氧扩散是开放还是关闭。在没有细菌的情况下，自溶和化学过程不足以完全降解胴体。在内部细菌存在的情况下，水柱细菌的存在或不存在对腐烂率几乎没有影响。最初的降解（前3天）主要影响角质层的脂质部分和胶原蛋白。后来的腐烂减少了不溶性蛋白质，增加了耐火结构成分（鞣制几丁质和胶原蛋白）的相对比例，到第30天超过95%。因此，在没有早期成岩矿化的情况下，只有硬化组织可能存活超过30天。因此，根据沉积记录中大分子（蛋白质-碳水化合物-脂质）的相对耐腐性预测的降解顺序并不能作为包含它们的结构组织保存潜力的一致指标。实验揭示了多毛类尸体腐烂的五个阶段；整个/萎缩，松弛，无支撑的肠，角质层囊，颚和刚毛。所有这些都在化石记录中有所体现。这样就可以估计出在被石化过程停止之前，衰变进行了多远。最完整的保存发生在寒武纪，那里的伯吉斯页岩保存了肌肉组织的证据。内脏和角质层的痕迹保存得更广泛，如在Mazon Creek， Gres a Voltzia， Solnhofen和Hakel。保存方式在各保护区各不相同。最常见的全身保存只包括较难抵抗的组织，颌骨（如果存在）和刚毛，并留下身体轮廓的印象。腐烂阶段可用作埋藏学阈值，以表明一个特别保存的生物群的多样性可能因埋藏学损失而减少的程度有多大。
A series of experiments was carried out to investigate the nature and controls (oxygen, microbial populations, agitation) on the degradation of soft tissues. Decay was monitored in terms of morphological change, weight loss, and change in chemical composition in the polychaete Nereis virens. Polychaetes include a range of tissue types of differing chemical composition and preservation potential: muscle, cuticle, setae, and jaws. Regardless of conditions, all the muscle had broken down and fluid loss through the ruptured cuticle had reduced the carcass to two dimensions within 8 days at 20-degrees-C. In most cases some cuticle, in addition to the jaws and setae, remained after 30 days. Where oxygen was completely eliminated, the rate of decay of the more volatile issues was significantly reduced. The degree of both osmotic uptake of water by the carcass and changes in water pH differed depending on whether the system was open or closed to oxygen diffusion. Autolytic and chemical processes are not sufficient to fully degrade the carcass in the absence of bacteria. Where internal bacteria are present, the presence or absence of water column bacteria made little difference to decay rate. Initial degradation (in the first 3 days) affects mainly the lipid fraction and the collagen of the cuticle. Later decay reduces the nonsoluble protein and increases the relative proportion of refractory structural components (tanned chitin and collagen) to more than 95% by day 30. Thus, only the sclerotized tissues are likely to survive beyond 30 days in the absence of early diagenetic mineralization. The sequence of degradation predicted from the relative decay resistance of macromolecules in the sedimentary record (protein - carbohydrate - lipid) is not, therefore, a consistent indicator of the preservation potential of structural tissues which incorporate them.The experiments reveal five stages in the decay of polychaete carcasses; whole/shriveled, flaccid, unsupported gut, cuticle sac, jaws and setae. All are represented in the fossil record. This allows an estimation of how far decay proceeded before it was halted by the fossilization process. The most complete preservations occur in the Cambrian where the Burgess Shale preserves evidence of muscle tissues. Traces of the gut and cuticle are more widely preserved, as at Mazon Creek, Gres a Voltzia, Solnhofen, and Hakel. Preservation varies within Konservat-Lagerstatten. The most common whole body preservation includes only the more recalcitrant tissues, jaws (where present) and setae, with an impression of the body outline. The stage of decay can be used as a taphonomic threshold, to provide an indication of how significantly the diversity of an exceptionally preserved biota is likely to have been reduced by taphonomic loss.