Collaborative Research: Estimating the Tempo of the Cambrian Explosion

标题：合作研究：估计寒武纪爆炸的节奏主要调查人员：Steve Wang，Susannah Porter，Adam Maloof Swarthmore College，University of California Santa Barbara和普林斯顿大学技术描述：由于最近在地质年代学、地层学和古生物学方面的进展，寒武纪爆炸的广泛模式现在是已知的，但这一事件的细节仍然不清楚，包括多样化的速度，主要分支的出现顺序，以及起源脉冲的数量和时间。这项工作的目标是为寒武纪最初~2500万年(Nemakit-Daldyian阶段和Tommotian阶段)骨骼动物的出现产生一个统计上严格的时间表。它将建立在PI、Maloof和Porter及其合作者早期工作的基础上，他们使用放射性校准的碳同位素化学地层学以200万年的分辨率重建了这段时间内的外观模式。这项工作表明，骨骼动物的多样化很早就开始了，并一直延续到整个时间间隔，出现的脉冲大约为540-538 Ma、534-530 Ma和524-522 Ma。然而，目前还不清楚保存偏见以及相关和测年方面的不确定性在多大程度上影响了这些模式。这里提出的研究将使用最近开发的统计方法来解决这些问题。具体地说，它将(1)使用由Pi Wang及其同事开发的新方法来估计多样化持续时间的置信度区间(从而提供其比率的估计)，以及(2)使用随机化程序和由Wang和一名本科生开发的新方法来识别最可能的起源脉冲的数量及其时间。作为附带好处，这项工作还将提供数据库中骨骼属起源时间的估计，以及恢复潜力和多样性曲线的估计。最后，这项工作将资助PIS Maloof和Porter以及研究生Moore正在进行的努力，以扩大数据集，目前包括来自中国、蒙古和西伯利亚24个剖面的150个骨骼属，最终目标是将覆盖范围扩大到晚寒武纪。非技术解释：寒武纪大爆发一直被认为是地球历史上最重要但最令人困惑的事件之一。这让达尔文感到困惑，他认为这是对他的想法的严重挑战。我们现在知道有一个前寒武纪的化石记录，达尔文并不知道，但寒武纪大爆发的意义仍然是无与伦比的：在大约30亿年主要是单细胞存在之后，多细胞生命突然(在地质时间尺度上)多样化，因为几乎所有主要的动物类型(门或身体平面)都出现在早寒武世。此外，在大约30亿年的软体存在之后，生命突然独立地进化出许多不同谱系中的矿化骨骼。我们仍然不知道是什么驱动了这一事件：生态(捕食者与猎物的相互作用)、生物学(发育工具包的变化)、环境(氧气水平的变化)或三者的某种组合。在这个项目中，我们首次尝试结合所有可用的地层学数据(同位素、生物地层学、地质年代学)，以拼凑出寒武纪生物和环境变化的详细记录。

Title: Collaborative Research: Estimating the Tempo of the Cambrian ExplosionPrinciple Investigators: Steve Wang, Susannah Porter, Adam MaloofSwarthmore College, University of California Santa Barbara, and Princeton UniversityTechnical description: Due to recent advances in geochronology, stratigraphy, and paleontology, the broad pattern of the Cambrian explosion is now known, but details of this event remain unclear, including the rate of diversification, the order of appearances of major clades, and the number and timing of pulses of origination. The goal of the work proposed here is to generate a statistically rigorous timeline for the appearances of skeletal animals during the first ~25 million years of the Cambrian(Nemakit-Daldynian and Tommotian stages). It will build on earlier work by PIs Maloof and Porter and their collaborators that used radiometrically calibrated carbon isotope chemostratigraphy to reconstruct the pattern of appearances through this interval at two million year resolution. That work suggested that the diversification of skeletal animals began early and extended throughout this interval, with pulses of appearances ca. 540-538 Ma, 534-530 Ma, and 524-522 Ma. However, it is not clear to what extent preservational biases and uncertainties in correlation and dating have influenced these patterns. The research proposed here will use recently developed statistical methods to address these concerns. In particular, it will (1) use a new method developed by PI Wang and colleagues to estimate a confidenceinterval for the duration of the diversification (and thus provide an estimate of its rate), and (2) use both a randomization procedure and a new method developed by Wang and an undergraduate student to identify the most likely number of pulses of origination and their timing. As a side benefit, this work will also provide estimates of the time of origination for the skeletal genera in the database, as well as estimates of recovery potential and diversity curves. Finally, this work will fund ongoing efforts by PIs Maloof and Porter and graduate student Moore to augment the dataset, currently composed of 150 skeletal genera from 24 sections in China, Mongolia, and Siberia, with the eventual goal of extending coverage to later Cambrian time.Non-technical explanation: The Cambrian Explosion has long been regarded as one of the most important but most perplexing events in Earth history. It puzzled Darwin, who thought it a serious challenge to his ideas. We now know that there is a Precambrian fossil record, of which Darwin was unaware, but the significance of the Cambrian Explosion is still unparalleled: after approximately 3 billion years of mostly unicellular existence, multicellular life suddenly (on geological timescales) diversified, as nearly all of the major 'types' of animals (phyla or body plans) appeared during the early Cambrian. Furthermore, after approximately 3 billion years of soft-bodied existence, life suddenly evolved mineralized skeletons in many different lineages independently. We still do not know what drove this event: ecology (predator-prey interactions), biology (changes in the developmental tool kit), environment (changes in oxygen levels) or some combination of all three. In this project, we attempt for the first time to combine all available stratigraphic data (isotopic, biostratigraphic, geochronologic) to piece together a detailed record of biological and environmental change in the Cambrian.