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Experimental decay of onychophorans - lobopodian anatomy and arthropod origins

有甲动物的实验性腐烂 - 叶足解剖学和节肢动物起源

基本信息

批准号：
NE/I016481/1
负责人：
Mark Purnell
金额：
$ 6.72万
依托单位：
University of Leicester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FI016481%2F1
关键词：
Experimental decay onychophorans lobopodian anatomy

项目摘要

The aims of this project are simple. By rotting velvet worms (onychophorans) under controlled conditions we will generate the data required to start correctly interpreting the fossil record of lobopodians. Accurate placement of lobopodians in the Tree of Life has the potential to resolve a major evolutionary problem: the origin of the arthropods. Arthropods are arguably the most successful animals on Earth: more diverse and abundant than any other group, they are important and familiar to everyone. Yet the identity of the arthropods' nearest living relatives, and the details of arthropod origins and early evolution remain unclear. In contrast to arthropods, onychophorans are both obscure and enigmatic. With their fat legs and body annulations they resemble a conga-line of overweight Michelin-men. A recent popular account of animal relationships noted that 'no group has prompted more zoological debate' (Tudge 2000, The Variety of Life) - exactly where onychophorans sit in the Tree of Life remains controversial. Surprisingly, answering the question of onychophoran relationships holds the key to unlocking the evolutionary emergence of the arthropods, and this is where fossil lobopodians have a major role to play. These extinct, soft-bodied organisms (almost all of Cambrian age) share a number of important anatomical features with onychophorans, but recent evolutionary analyses suggest that fossil lobopodians include the ancestors of arthropods, of onychophorans, and of panarthropods (the larger group to which both onychophorans & arthropods belong). Consequently, finding the correct places for fossil lobopodians in the Tree of Life has the potential to reveal the sequence in which important characteristics of arthropods and onychophorans were acquired. If lobopodian branches do fill the gap between living onychophorans and arthropods, we may be able to resolve relationships between the major arthropod branches. This potential can only be realised with correct placement of lobopodians, and this requires new information about how they decayed. Much of the current disagreement over the placement of lobopodians arises because we don't understand how the process of decay affected their bodies prior to fossilization. Studies of other organisms show that decay rapidly alters the appearance of important anatomical features. As soft tissues rot and collapse the shape and juxtaposition of body parts - crucial criteria for anatomical comparison - change significantly. Other features rot away completely. We need new data so that these changes, which will have affected all fossil lobopodians to some degree, can be taken into account when interpreting their anatomy. We will employ a new approach to the experimental study of how animals decay, recently developed in our lab. We will rot onychophorans under controlled lab conditions and carefully record their important anatomical features (many of which they share with fossil lobopodians) at timed intervals as they decompose. From this we will determine the rate and sequence of decay of features; when and how their juxtaposition, shape and appearance change. This will allow us to establish criteria for the recognition of decay-transformed features in fossil lobopodians and reassess the anatomy and evolutionary relationships of these controversial animals (including exceptionally well-preserved new material). It will also allow us to further test a hypothesis developed from our ongoing decay experiments: that the decay of evolutionarily important anatomical features of soft bodied animals is not random - features that are most useful for recognizing evolutionary relationships are the most likely to decay rapidly. If this pattern is widespread it is an important yet previously unrecognised bias in reconstructing the evolutionary relationships of fossils.

这个项目的目的很简单。通过在受控条件下腐烂天鹅绒蠕虫（onychophorans），我们将产生开始正确解释lobopodians化石记录所需的数据。在生命之树中准确地定位叶足类有可能解决一个主要的进化问题：节肢动物的起源。节肢动物可以说是地球上最成功的动物：比任何其他群体都更多样化和丰富，它们对每个人都很重要和熟悉。然而，节肢动物最近的亲属的身份，以及节肢动物起源和早期进化的细节仍然不清楚。与节肢动物相比，爪类动物既晦涩又神秘。他们肥胖的腿和身体的环形，就像一排超重的米其林男人。最近一个关于动物关系的流行描述指出，“没有任何一个群体引发了更多的动物学辩论”（Tudge 2000，The Variety of Life）--确切地说，有爪类动物在生命之树中的位置仍然存在争议。令人惊讶的是，回答onychophoran关系的问题是解开节肢动物进化出现的关键，这就是化石lobopodians发挥重要作用的地方。这些已灭绝的软体生物（几乎都是寒武纪时期的）与有蹄类有许多重要的解剖学特征，但最近的进化分析表明，化石lobopodians包括节肢动物，有蹄类和泛节肢动物的祖先（有蹄类和节肢动物都属于较大的群体）。因此，找到正确的地方lobopodians化石在生命之树有可能揭示的序列中的重要特征的节肢动物和onychophorans收购。如果叶足类分支确实填补了活的有蹄类和节肢动物之间的差距，我们也许能够解决主要节肢动物分支之间的关系。这种潜力只能通过正确放置lobopodians来实现，这需要关于它们如何腐烂的新信息。目前关于叶足类的位置的许多分歧都是因为我们不了解在化石化之前腐烂的过程如何影响它们的身体。对其他生物的研究表明，腐烂会迅速改变重要的解剖特征。随着软组织的腐烂和塌陷，身体各部分的形状和并列位置--解剖学比较的关键标准--发生了显著变化。其他特征完全腐烂。我们需要新的数据，以便在解释它们的解剖结构时，能够考虑到这些变化，这些变化将在某种程度上影响所有的化石lobopodians。我们将采用我们实验室最近开发的一种新方法来进行动物如何腐烂的实验研究。我们将在受控的实验室条件下腐烂甲科动物，并在它们分解时每隔一段时间仔细记录它们的重要解剖特征（其中许多特征与叶足类化石相同）。由此，我们将确定特征衰变的速率和顺序;它们的并置、形状和外观何时以及如何变化。这将使我们能够建立识别lobopodians化石中腐烂转化特征的标准，并重新评估这些有争议的动物（包括保存异常完好的新材料）的解剖学和进化关系。这也将使我们能够进一步验证我们正在进行的衰变实验中提出的一个假设：软体动物进化上重要的解剖特征的衰变不是随机的--对识别进化关系最有用的特征最有可能迅速衰变。如果这种模式是普遍的，这是一个重要的，但以前未被承认的偏见，在重建化石的进化关系。