Collaborative Research: Estimating the Tempo of the Cambrian Explosion

职务名称：合作研究：估计寒武纪大爆炸的克里思速度主要研究人员：Steve Wang，Susannah Porter，Adam Maloof Swarthmore学院，加州大学圣巴巴拉分校和普林斯顿大学技术描述：由于地质年代学、地层学和古生物学的最新进展，现在已经知道了寒武纪大爆发的广泛模式，但这一事件的细节仍不清楚，包括多样化的速度，主要分支出现的顺序，以及起源脉冲的数量和时间。这里提出的工作的目标是生成一个严格的统计时间轴的骨骼动物的外观在寒武纪（Nemakit-Daldynian和Tommotian阶段）的第一个~25万年。它将建立在PI Maloof和Porter及其合作者的早期工作基础上，这些工作使用辐射校准的碳同位素化学地层学来重建这段时间内的外观模式，分辨率为200万年。这项工作表明，骨骼动物的多样性很早就开始了，并在整个这段时间内延伸，出现的脉冲大约是1000年。540-538 Ma、534-530 Ma和524-522 Ma。然而，目前尚不清楚在多大程度上的相关性和日期的不确定性和偏见影响了这些模式。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。特别是，它将（1）使用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区间（从而提供其速率的估计），以及（2）使用随机化程序和Wang和一名本科生开发的新方法来确定最可能的起源脉冲数及其时间。作为一个附带的好处，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，这项工作将资助正在进行的努力，由PI马鲁夫和波特和研究生摩尔，以扩大数据集，目前由150个骨骼属，从24个部分在中国，蒙古和西伯利亚，最终的目标是扩大覆盖范围晚寒武纪时间。非技术性的解释：寒武纪大爆发一直被认为是最重要的，但最令人困惑的事件之一，在地球历史上。这使达尔文感到困惑，他认为这是对他的观点的严重挑战。我们现在知道，有一个前寒武纪的化石记录，其中达尔文不知道，但寒武纪爆发的意义仍然是无与伦比的：经过大约30亿年的主要单细胞存在，多细胞生命突然（在地质时间尺度上）多样化，因为几乎所有的主要“类型”的动物（门或身体计划）都出现在寒武纪早期。此外，经过大约30亿年的软体存在，生命突然独立地在许多不同的谱系中进化出矿化的骨骼。我们仍然不知道是什么推动了这一事件：生态学（捕食者-猎物相互作用），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，我们第一次尝试联合收割机结合所有可用的地层数据（同位素，生物地层，地质年代学）拼凑在一起的生物和环境变化的详细记录在寒武纪。

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.