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

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.

Benefits to the UK

Biodiversity loss is a global (rather than national) concern. This proposal offers insights into the manner in which species are likely to respond to severe environmental challenges. It offers the opportunity to formulate general rules concerning the morphological, developmental, behavioural and ecological attributes that increase extinction risk, and that promote the recovery and diversification of lineages in the wake of environmental crises. Any improvement in our understanding of the dynamics of mass extinctions have huge potential to inform policy and thereby reduce present and projected rates of biodiversity loss. It is notoriously difficult to estimate the economic value of biodiversity and ecosystem services. Conservationists also face a dilemma when attempting to ascribe monetary value. On one hand, a figure can potentially be weighed against something else to its detriment. On the other hand, there has been a tendency to assume that 'invaluable' or inestimable things have no value. The loss of biodiversity has been estimated to cost in the region of £40 billion per annum. While these figures are not currently included in GDP estimates, a loss equivalent to 7% of GDP is projected by 2050 at current rates of extinction. Moreover, a diverse environment is one that greatly enhances the quality of life: something that is even more difficult to quantify.

Benefits to academics

The outputs of this project will be of benefit to all those palaeontologists, evolutionary biologists and conservation planners with an interest in the dynamics and selectivity of mass extinctions. We will also determine whether it is possible to identify attributes that promote success during post-extinction recovery.
Our work is also of great relevance to those seeking to understand the relationship between different modes of developmental change within lineages and the disparity of adult form. This encompasses evolutionary developmental (evo-devo) biology. It will also be of immediate application to all those interested in quantifying the manner in which clades evolve through their morphological, functional and developmental spaces.
The outputs of the program will be of great value to all ammonite palaeobiologists. This will reinforce the importance and utility of ammonoids as a model system for macroevolutionary studies.
All of the software that we develop will be of the widest possible application to other morphospatial, allometric and hydrodynamic questions. Code for mapping taxa within their morphospaces, allometric and function spaces will be made available online, as will GPL Licensed code for our new Lagrangian Vortex software.

Public understanding

There is enormous public concern about present rates of extinction and biodiversity loss. Mass extinctions are, perhaps, the best known of all palaeontological and evolutionary phenomena, and have an immediate popular appeal. Moreover, ammonites are familiar to most non-scientists and amongst the most iconic of all fossil groups. These factors give us a considerable head start in communicating the implications of our research to the public. In particular, we will relate past extinction selectivity in response to environmental crises to the current dynamics of biodiversity loss. The appeal of these themes will be enhanced by highly accessible visual elements: videos of flume tank experiments; remote controlled, self-propelled ammonites; 3D renderings and animations. Bath has excellent mechanisms to ensure that we maximise the impact of our work in all media.

Career development for staff

For the PDRA and the Co-I: Transferable skills applicable to other palaeontological or engineering projects. Skills in writing and oral presentation; programming and statistical analysis; science communication; advanced imaging techniques.