Susceptibility to mass extinctions: Ammonites as a case study for integrating morphological, developmental, phylogenetic and biomechanical data

生物多样性目前的丧失速度是否意味着我们正在进入可与地质历史上的“五大灭绝”相媲美的第六次“大灭绝”？如果是这样的话，我们能否预测哪些物种可能受到最严重的打击，以及是否有可能确定哪些物种最有可能在环境灾难之后重新辐射和多样化？如果是这样的话，我们能否更广泛地将这些发现用于全球保护规划？回答这些问题的一种方法是跟踪一个大群体的进化，这个大群体反复遭受大规模灭绝的打击，但其中多个血统幸存下来，以便重新辐射。化石记录了一系列复杂的自然实验，使我们能够对进化树的不同分支和多个大灭绝事件中发生的平行现象进行概括。菊石可能是所有化石中最具标志性的，也是最容易辨认的，它拥有非常适合这一目的的特殊化石记录。菊石起源于泥盆纪，经历了泥盆纪末、二叠纪末和三叠纪末的大规模灭绝事件，然后在白垩纪末消亡。由于其他几个原因，菊石特别适合于灭绝选择性的研究。首先，它们的壳通过堆积成(通常)螺旋形的腔体生长，这样所有胚胎后阶段都会一起化石。这一点很重要，因为它让我们能够解释形态上的发育变化(以及相关的生活方式变化)。其次，大多数菊石的外壳可以非常简单地在理论形态空间中建模，也可以在更复杂的经验形态空间中建模。在连续的大规模灭绝事件中，这些空间的人口减少的方式(例如，极端形态的首先灭绝与随机灭绝)将揭示灭绝选择性的本质。此外，通过对异速生长和其他发育空间的发展轨迹进行建模，我们可以进一步测试特定的增长模式是否会增加灭绝的风险，或者在环境危机后促进谱系的辐射。使用菊石的第三个优点是(与几乎任何其他游泳动物不同)，它们的身体不会因为运动而变形。这使得它们特别适合于流体力学研究。是否有这样的生物力学特性与灭绝风险相关？菊石能够通过喷气推进游泳；反复从地幔内的虹吸管喷水。我们将使用两种互补的方法：计算流体力学和水箱中的物理模型来模拟它们的游泳和操纵能力有多好、多快、多有效。对于前一种方法，我们将编写比标准计算流体动力学(CFD)包更适合于模拟运动和旋转物体周围复杂流动的新软件。对于后者，我们将在各种媒体中使用结构光或CT扫描与3D打印相结合，以产生逼真的加权和平衡模型。计算机设计将进一步使我们能够在理论形态空间内对任何潜在的菊石形态进行虚拟和物理测试。难道许多物理上可能的几何形状没有实现，是因为它们具有不希望看到的流体力学性质吗？菊石是否反复地聚集在同一个有效设计的小样本上？或者，在形态空间的某些区域中菊石属的密集分布是否反映了这些区域的水动力参数的广泛差异(以及相关的生态位空间的更精细划分)？该项目的一个中心目标是使我们的所有数据、计算机代码、软件、代表性视频和结果尽可能广泛地提供给学术界、教育用户和公众。所有这些都将在知识共享(CC0)和OSI批准的许可证下发布，我们将促进它们在自然科学的其他领域重新使用和再利用。

Do present rates of biodiversity loss imply that we are entering a sixth 'mass extinction' comparable to the 'big five' of the geological past? If so, can we predict which species are likely to be hardest hit, and is it possible to identify those groups most likely to re-radiate and diversify in the wake of environmental catastrophe? If so, can we use these findings more broadly for global conservation planning? One way to answer these questions is to follow the evolution of a large group that has repeatedly been hit by mass extinctions, but in which multiple lineages have survived in order to re-radiate. Fossils record a complex series of natural experiments that allow us to make generalisations about parallel phenomena occurring in different branches of the evolutionary tree, and at multiple mass extinction events. Ammonites - perhaps the most iconic and instantly recognisable of all fossil groups - have an exceptional fossil record that is ideally suited for this purpose. Originating in the Devonian they transit the end Devonian, end Permian and end Triassic mass extinction events prior to their demise at the end Cretaceous.Ammonites are uniquely suited to a study of extinction selectivity for several other reasons. Firstly, their shells grow by accreting chambers into a (typically) spiral form, such that all post-embryonic stages are fossilized together. This is important because it allows us to account for developmental changes in morphology (and associated shifts in mode of life). Secondly, the external shells of most ammonites can be modeled very simply in a theoretical morphospace, as well as in more complex empirical morphospaces. The manner in which these spaces are depopulated (e.g., the extinction of extreme morphologies first versus random extinction) at successive mass extinction events will reveal the nature of extinction selectivity. Additionally, by modeling developmental trajectories in allometric and other developmental spaces, we can further test whether particular growth patterns increase the risk of extinction, or promote the radiation of lineages after environmental crises. A third advantage of using ammonites is that (unlike virtually any other swimming animals) their bodies do not deform for locomotion. This makes them particularly suitable for hydrodynamic studies. Do any such biomechanical properties correlate with extinction risk? Ammonites were able to swim by jet propulsion; repeatedly squirting water from a siphon within the mantle. We will model how well, fast and efficiently they were able to swim and manoeuvre using two complementary methods; computational fluid dynamics and physical modeling in water tanks. For the former approach, we will write new software much better-suited to simulating the complex flow around moving and rotating bodies than standard computational fluid dynamics (CFD) packages. For the latter we will use structured light or CT scanning coupled with 3D printing in a variety of media to yield realistically weighted and balanced models. Computer design will further enable us to virtually and physically test any potential ammonite morphology from within the theoretical morphospace. Were many physically possible geometries not realised because they had undesirable hydrodynamic properties, and did ammonites repeatedly converge on the same small sample of efficient designs? Or does the dense packing of ammonite genera in certain regions of morphospace reflect wide variation in hydrodynamic parameters in these same regions (and an associated finer subdivision of niche space)?A central objective of this project is to make all of our data, computer code, software, representative video and results available to the widest possible community of academics, educational users and the public. All will be released under Creative Commons (CC0) and OSI approved licenses, and we will promote their re-use and repurposing in other fields of the natural sciences.