5亿年前的化石解开了地球生命进化的百年之谜

艺术家对大约 5.14 亿年前寒武纪海底生活中的 Gangtocunia aspera 的重建。 前景中的部分个体骨骼被移除以显示骨骼内的软肿瘤。 信用：王晓东重建

科学家们终于能够解开地球上生命进化中的一个数百年之久的谜团，揭示了第一批制造骨骼的动物的样子。 这一发现得益于在中国云南省东部发现的保存完好的化石收藏。 研究结果于 11 月 2 日发表在科学期刊上 英国皇家学会学报 B.

在大约 550 到 5.2 亿年前的一次名为寒武纪大爆发的事件中，在地质学的眨眼之间，化石记录中突然出现了第一批能够建造坚韧骨骼的动物。 这些早期化石中有许多是简单的空心管，长度从几毫米到几厘米不等。 然而，制造这些骨骼的动物类型几乎完全未知，因为它们缺乏将它们识别为今天仍然活着的主要动物群体所需的柔软部分的保存。

Gangtoconia aspera 的化石标本（左）和示意图（右）保存了软组织，包括肠道和触手。 学分：卢克·帕里和张光旭

四个样品 甘托科尼亚 由于软组织（包括肠子和口腔部分）仍然完好无损，它被包含在 5.14 亿年的新化石组中。 这些揭示了该物种的嘴被一圈约 5 毫米（0.2 英寸）长的光滑、不分枝的爪环所包围。 这些很可能被用来刺痛和捕捉猎物，例如小型节肢动物。 发掘也表明 甘托昆亚 他有一个盲肠（仅一端开口），分为内腔，填充管子的长度。

这些特征今天仅在现代水母、海葵及其近亲（称为刺胞动物）中发现，这些生物的柔软部分在化石记录中极为罕见。 研究表明，这些简单的动物是最早建造构成大部分已知化石记录的坚固骨骼的动物之一。

据研究人员称， 甘托昆亚 它看起来类似于现代的scyphozoan水母，具有固定在基本基质上的刚性管状结构。 触手的嘴伸出管子，但可以缩回管子内以避免捕食者。 与活水母的息肉不同，管 甘托昆亚 由磷酸钙制成，这是一种构成牙齿和骨骼的坚硬矿物质。 随着时间的推移，使用这些材料建造骨骼在动物中变得越来越少见。

帮派的 Tokunia aspera 嘴部的特写，展示了可以用来捕捉猎物的触手。 学分：卢克·帕里和张光旭

通讯作者 Dr. 卢克·巴里，地球科学系，[{” attribute=””>University of Oxford, said: “This really is a one-in-million discovery. These mysterious tubes are often found in groups of hundreds of individuals, but until now they have been regarded as ‘problematic’ fossils, because we had no way of classifying them. Thanks to these extraordinary new specimens, a key piece of the evolutionary puzzle has been put firmly in place.”

The new specimens clearly demonstrate that Gangtoucunia was not related to annelid worms (earthworms, polychaetes and their relatives) as had been previously suggested for similar fossils. It is now clear that Gangtoucunia’s body had a smooth exterior and a gut partitioned longitudinally, whereas annelids have segmented bodies with transverse partitioning of the body.

The fossil was found at a site in the Gaoloufang section in Kunming, eastern Yunnan Province, China. Here, anaerobic (oxygen-poor) conditions limit the presence of bacteria that normally degrade soft tissues in fossils.

Fossil specimen of Gangtoucunia aspera preserving soft tissues, including the gut and tentacles (left and middle). The drawing at the right illustrates the visible anatomical features in the fossil specimens. Credit: Luke Parry and Guangxu Zhang

PhD student Guangxu Zhang, who collected and discovered the specimens, said: “The first time I discovered the pink soft tissue on top of a Gangtoucunia tube, I was surprised and confused about what they were. In the following month, I found three more specimens with soft tissue preservation, which was very exciting and made me rethink the affinity of Gangtoucunia. The soft tissue of Gangtoucunia, particularly the tentacles, reveals that it is certainly not a priapulid-like worm as previous studies suggested, but more like a coral, and then I realised that it is a cnidarian.”

Although the fossil clearly shows that Gangtoucunia was a primitive jellyfish, this doesn’t rule out the possibility that other early tube-fossil species looked very different. From Cambrian rocks in Yunnan province, the research team has previously found well-preserved tube fossils that could be identified as priapulids (marine worms), lobopodians (worms with paired legs, closely related to arthropods today), and annelids.

Co-corresponding author Xiaoya Ma (Yunnan University and University of Exeter) said: “A tubicolous mode of life seems to have become increasingly common in the Cambrian, which might be an adaptive response to increasing predation pressure in the early Cambrian. This study demonstrates that exceptional soft-tissue preservation is crucial for us to understand these ancient animals.”

Reference: “Exceptional soft tissue preservation reveals a cnidarian affinity for a Cambrian phosphatic tubicolous enigma” by Guangxu Zhang, Luke A. Parry, Jakob Vinther and Xiaoya Ma, 2 November 2022, Proceedings of the Royal Society B Biological Sciences.
DOI: 10.1098/rspb.2022.1623