Team Paleontology PAL

(Catherine Crônier)

Insights into large-scale changes in (paleo-)ecosystems based on integrative studies of evolutionary and paleoecological dynamics

Based on qualitative and quantitative approaches the Paleontology team aspires to address a number of scientific questions that are of relevance to paleobiology, macroevolution and macroecology. Historically, but not exclusively, focused on Paleozoic lineages, we study the fossil record of protistan, plant and animal biological models to answer eco-evolutionary questions. Overall, we search to identify the underlying ecological and evolutionary drivers operating at the scale of geological time, as well as biotic and abiotic factors that have contributed to the observed patterns in paleobiodiversity, i.e. dynamic changes in the balance of speciation and extinction. We are interested in unraveling the biotic response to environmental change, at both regional and global scale, including the emergence of new body plans and appearance of key innovations. Our strategies include, among others approaches, the quantification and comparison of patterns in taxonomic diversity versus morphological disparity, the documentation of morphological changes correlated to environmental factors, the reconstruction of paleoecosystems, and attempts to infer underlying processes from the observed patterns.

Our team aims to develop integrative studies that attempt to address macroevolutionary and macroecological questions in order to highlight evolutionary and ecological processes operating over various timescales, as well as the various ways that these interact. We aspire to create a combined view and understanding of paleobiodiversity, global environmental change (including climate change) and ecosystem complexity; in addition, we are investigating shape changes in terms of evolution and adaptation within lineages, the link between microevolution and macroevolution, and the ecological interactions within marine and terrestrial ecosystems.

The activities of the team will be structured around three research axes:

• Paleobiodiversity dynamics in deep time: Understanding the impact of climate change on extinctions in marine and terrestrial ecosystems, collapse thresholds and post-crisis recoveries. Moderator Borja Cascales-Miñana
• Tempo and mode of morphological evolution: Deciphering the message of shape changes in terms of evolution and adaptation; exploring the link between microevolutionary and macroevolutionary processes. Moderator Bert VAN BOCXLAER
• Paleoecosystem reconstructions: Understanding how ecosystems were structured in the past and how global change may have affected their structure, ecospace filling and biogeographic distribution; insights from comparison with modern analogues. Moderator Sébastien CLAUSEN

General objectives

Large scale paleogeographic changes modified environmental conditions. Tectonic plate re-organisation (recombination or fragmentation of continents), on the one hand, and extreme climatic change, on the other, may have partly controlled the restructuring of ancient biological systems and led to mass extinctions (Sepkoski 1981). These crises appear to have been often caused by drastic changes in Earth's climate. Today, our planet becomes increasingly warmer and faces (1) a major crisis in biodiversity and (2) the loss of key biotic component for a balanced ecosystem functioning.
Morevover, major diversifications in the marine biosphere, such as the Cambrian Explosion, the Great Ordovician Biodiversification Event (GOBE) and the Mid-Paleozoic Marine Revolution have been envisioned either as discrete events or as a protracted macroevolutionary event that shaped marine life for the rest of the Phanerozoic (Harper et al. 2015; Servais et al. 2015; Signor & Brett 1984). For example, several authors emphasize the Cambrian roots of the GOBE; a correlation with the Devonian Pelagic Revolution may be envisioned when demersal and planktic organisms, as well as pelagic swimmers (e.g. some arthropods, early cephalopods, graptoloids) began to conquer the water column, in a general context of drastic increase in predation pressure (cf. Klug et al. 2010).
A large variety of explanations, either of biotic or abiotic origin, were put forward regarding the cause of these events (see Miller 2012; Rasmussen et al. 2016). Recent studies on the biological triggers of diversifications mainly highlight strong changes in the oceanic food-webs and the occupation of the water column by different organisms as most influential (Servais et al. 2008, 2015; Klug et al. 2010).

In this context, our goal is to develop paleobiological databases covering various temporal and geographic scales in order to document biodiversity changes in a number of clades over geological time, and explore the possible drivers behind these changes. Our team is and will continue testing biodiversity curves by evaluating the various biases introduced; we will continue updating biodiversity curves, by highlighting the radiation and extinction phases in relation to environmental conditions, both at globally in deep time (Crônier et al. 2013; Nowak et al. 2015; Tétard et al. 2017) and regionally in the recent past (Van Bocxlaer 2017). In the long term, we wish to compare biodiversity curves obtained for different ecological groups of organisms, and the evolution of their morphological space, in order to understand their interactions. Our databases and these curves could then be used to calculate speciation and extinction rates, or be combined with morphological data. It will then become possible to examine whether speciations and extinctions are confined to specific regions of morphospace, or not.

For some lineages the fossil record may have been documented with exceptional paleontological control so that morphological evolution may be related to quantitative genetic theory, and we will aim to continue expanding the limits of current knowledge in this subject (Van Bocxlaer & Hunt 2013).
To study the evolution of organisms and past ecosystems more efficiently, we intend to use specimen-based approaches (including fieldwork, taxonomic descriptions, taphonomic studies, biostratigraphy…) in combination with modern analytical tools based on modelling approaches and innovative statistical methods, which in part are developed in-house. Morphometric studies will better constrain the actual number of biological species by controlling intra-specific variability and will provide information on the changes that took place in the timing and the rate of development of morphological features; they may also help to better assess the impact of environmental changes on changes in morphology. On the one hand, we need to better understand the relationships between biodiversity and environmental change; for example, to what extent organisms have adapted (evolution) or rather migrated and interacted (ecology) to face changing environments? On the other hand, we study the relation between taxonomic richness, or thus diversity, and morphological disparity. Understanding this relation could allow recognizing the main types of environments and associated ecological parameters (temperature, light, hydrodynamism...) influencing biodiversity. We intend to explore the past ecological networks and their evolution and to investigate the evolution of ecological interactions through time (including competition and predation) and their impact on the ecosystem complexity.

Research Operations

This research project is to explore how taxa responded to various global or local biotic crises, how these crises have affected ecosystem functioning, and to what extent changes result from evolutionary (adaptation) and ecological processes (migration/species interactions). Pertinent scientific questions in this respect are:
How are taxonomic, morphological and phylogenetic diversity related to one another through geological time, during mass extinctions and crisis entry and exit phases?
Is there evidence of density-dependence on global and regional scales?
What are the links and the space-time occupation strategies developed between faunas?
What is the relationship between the adult body size of species, their phylogeny, their life span, their type of development, their geographic distribution, and their latitudinal position?
How does diversity respond to paleoenvironmental changes? What are the relationships with environmental proxies?
What is the point of no return for irreversible erosion of biodiversity in the face of environmental changes?