Decay of velvet worms (Onychophora), and bias in the fossil record of lobopodians.
Decay of velvet worms (Onychophora), and bias in the fossil record of lobopodians.
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DOI：
10.1186/s12862-014-0222-z
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发表时间：
2014-11-29
影响因子：
3.4
通讯作者：
Purnell MA
中科院分区：
文献类型：
--
作者：
Murdock DJ;Gabbott SE;Mayer G;Purnell MA
化石lobopodians，包括动物提出有密切的亲和力，现代onychophorans，是至关重要的，以了解泛节肢动物的身体计划和蜕皮动物群体之间的门级关系的演变。不幸的是，它们的解剖结构的关键特征是未矿化的，并且在死亡，腐烂和保存过程中引入了偏见，但这些化石在多大程度上受到死后腐烂过程的影响是完全未经测试的。最近对脊索动物的实验工作强调了腐烂引起的深刻偏见，导致将严重腐烂的标本错误地解释为分支的原始成员（stemward滑动）。这种偏差对脊索动物以外的生物体的影响程度尚不清楚。在这里，我们使用实验的天鹅绒蠕虫（Onychophora）的衰变检查化石lobopodians的衰变偏见的重要性。虽然我们发现向干滑动在非矿化的Lobopodian化石的解释中并不重要，但腐烂的影响远非无偏的。定量分析揭示了腐烂过程中身体比例的显着变化、解剖特征中的腐烂阻力谱以及拓扑相关特征的相关腐烂。这些结果对解释化石lobopodian仍然具有重要意义，表明身体轮廓和相对比例等特征对于分类学或系统发育重建是不可靠的，除非考虑到腐烂。同样，非独立的字符的损失，由于并置在体内，在腐烂过程中有可能偏向非生物矿化化石的系统发育分析。我们的研究结果很难与最近描述的寒武纪lobopodians高度腐烂的组织和结构，如神经组织和复杂的肌肉组织的解释相一致。更广泛地说，我们假设，stemward滑动是不太可能是一个重要的因素之间的埋藏偏见，影响生物体的解剖结构的耐腐功能丰富的遗传信息字符。相反，具有抗腐烂的身体部位但具有集中在易腐烂组织中的信息特征的生物体与那些缺乏抗腐烂身体部位的生物体一样容易受到偏见的影响。需要对衰变进行进一步的实验分析来检验这些假设。本文的在线版本（doi：10.1186/s12862-014-0222-z）包含补充材料，可供授权用户使用。
Fossil lobopodians, including animals proposed to have close affinity to modern onychophorans, are crucial to understanding the evolution of the panarthropod body plan and the phylum-level relationships between the ecdysozoan groups. Unfortunately, the key features of their anatomy are un-mineralized and subject to biases introduced during death, decay and preservation, yet the extent to which these fossils have been affected by the processes of post-mortem decay is entirely untested. Recent experimental work on chordates has highlighted a profound bias caused by decay, resulting in the erroneous interpretation of badly decayed specimens as primitive members of a clade (stemward slippage). The degree to which this bias affects organisms other than chordates is unknown. Here we use experimental decay of velvet worms (Onychophora) to examine the importance of decay bias in fossil lobopodians. Although we find stemward slippage is not significant in the interpretation of non-mineralized lobopodian fossils, the affect of decay is far from unbiased. Quantitative analysis reveals significant changes in body proportions during decay, a spectrum of decay resistance across anatomical features, and correlated decay of topologically associated characters. These results have significant implications for the interpretation of fossil lobopodian remains, demonstrating that features such as body outline and relative proportions are unreliable for taxonomy or phylogenetic reconstruction, unless decay is taken into account. Similarly, the non-independent loss of characters, due to juxtaposition in the body, during decay has the potential to bias phylogenetic analyses of non-biomineralized fossils. Our results are difficult to reconcile with interpretations of highly decay-prone tissues and structures, such as neural tissue, and complex musculature, in recently described Cambrian lobopodians. More broadly, we hypothesize that stemward slippage is unlikely to be a significant factor among the taphonomic biases that have affected organisms where decay-resistant features of the anatomy are rich in phylogenetically informative characters. Conversely, organisms which possess decay-resistant body parts but have informative characters concentrated in decay-prone tissues will be just as liable to bias as those that lack decay-resistant body parts. Further experimental analysis of decay is required to test these hypotheses. The online version of this article (doi:10.1186/s12862-014-0222-z) contains supplementary material, which is available to authorized users.
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