无论您是爱它们，还是无法忍受它们，都不能否认节肢动物是地球上最成功的动物群体，代表着惊人的80％的已知物种。从海底到最高的永久栖息地，节肢动物几乎可以在生活中的任何地方找到。它们几乎构成了几乎每个生态系统的组成部分，它们将自己巩固为当今地球上最重要的动物。

但是，为了完全了解节肢动物的多样性，我们必须首先考虑它们的起源。幸运的是，生存节肢动物群（螯合物，甲壳类动物，昆虫，米尔里亚植物）之间的大规模进化关系得到了相当大的一致性。如果我们向后追踪节肢动物的家谱，我们可以看到昆虫和甲壳类动物形成最接近的树枝，然后米尔里亚木无是下一步的，最后是螯合物。但是，作为古生物学家，总会有一个迫切的问题：“但是在此之前发生了什么？”

Following the tree even further back, beyond what we’d classify as an arthropod, we meet the tardigrades (waterbears/moss piglets), the onychophorans (velvet worms) and, ancestral to all the branches we’ve mentioned so far, are the extinct lobopodians (which mostly resemble spiny worms with legs). This whole expanded group of ‘arthropods and their closest relatives’ is called the Panarthropoda and it is here, with the fossilised lobopodians, that we can discover what the ancestor of most animal species on the planet might have looked like.

This might sound obvious; if the lobopodians are at the base of a tree, then they will surely be the closest approximation to what the ancestor of all members of that group looks like. This is practicably correct, technically incorrect and a massive simplification, all at the same time.

确定Panarthropod家族树的基础的问题是两个折叠：

首先，由于小叶植物都是灭绝的，因此我们无法像与生物物种一样获得他们的分子数据（例如DNA）来构建其家谱。同样，基于现代分子数据的树木不能告诉我们有关化石物种的太多信息。因此，我们必须转向化石记录以及其中持有的解剖信息，这是唯一的证据。

Secondly, when we examine the oldest lobopodian fossils we can find, they already exhibit high levels of diversity and disparity; there are already lots of them and they’re already different from each other. Amongst all these different kinds of contemporary lobopodians, it’s hard to point at one and say ‘this is the one that best represents the ancestral state’.

现在，一个新的化石洛博植物正在允许对Panarthropodan祖先的外观进行修订。Caron＆Aria置于系统发育分析（发现最可能的家谱的定量方法）中Ovatiovermis cribratusto be the most primitive member of the panarthropods.

Ovatiovermis被发现在世界著名,half-billion-year-old, fossil lagerstätte (site of special preservation) called the Burgess Shale, in British Columbia, Canada. It possesses the typical worm-like body and smooth legs of the lobopodians, but is unique in that it lacks the defensive spines common in many of its kin. Its body is differentiated from anterior to posterior; the anterior is slender, with long legs which host a double-row of bristles, whilst the posterior is much thicker and robust, with short stubby legs, looking much like root ginger.

The lifestyle ofOvatiovermis已被解释为滤滤器的后肢，并用齿前肢梳理食物的水柱。这种解释很重要，因为它在树的基部显示了这种解剖结构的特定功能。因此，可以推断出拥有这些特征的树下的任何后续物种都可以从具有相似生态的祖先遗传为遗传。因此，我们可以说，panarthropods是从过滤式祖先演变而来的。

WellOvatiovermis（（Ovatio– Ovation,vermis- 蠕虫），您已经透露，> 80％的动物物种的祖先是过滤器，站起来，给自己掌声！

重建Ovatiovermis cribratusshowing its purported anchored position and frontal lobopods for suspension feeding. Life reconstruction. (Animation by Lars Fields).