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PhD Defense - Louise SOUQUET

Patterns of intra-specific variation and covariation in conodont elements.
When Dec 18, 2018
from 02:00 PM to 04:30 PM
Where Amphi SVT à confirmer
Contact Name Louise Souquet
Attendees Zollikofer, Christoph, Professeur, Universität Zürich, Rapporteur
Corradini, Carlo, Professeur, Università degli studi di Cagliari, Rapporteur
Ponce de León, Marcia, Senior ressearcher, Universität Zürich, Examinatrice
Khila Abderrahman, Directeur de recherche, ENS de Lyon, Examinateur
Goudemand, Nicolas, Professeur, ENS de Lyon, Directeur de thèse
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Evolution is the result of two main factors: the environment and the development. In this context, untangling the impact of these two forces on the morphological evolution of a structure is of major importance. To do so, studying evolution in deep time is useful, as it is the only way to observe the mechanisms in action over a long time interval and the responses to major environmental variations. In this thesis, we aim to better understand the evolution of a fossil species: the conodont. These marine jawless vertebrates possess a feeding apparatus composed of mineralized structures comparable to teeth, called conodont elements. Their high evolutionary rate, their long and sub-continuous fossil record, and their large populations made them a relevant model to conduct evolutionary studies in deep time. In the literature, only a few studies attempt to quantify the shape of conodont elements, and never in a developmental framework. With the discovery of new exceptionally preserved fossils, and the establishment of a methodology to quantify the patterns of morphological variation and covariations in these elements, the morphological evolution of conodont elements have been studied from different angles. We have established the existence of covariations between some morphological characters, illustrating the constraints on possible morphologies. Some constraints are considered developmental, while others are potentially mechanical. Evolutionary directions are highlighted, channelled by developmental constraints. At the inter-genera scale, we demonstrated a relationship between environmental changes (especially temperature variations) and these evolutionary directions. The results revealed a combined effect of the developmental forces (that constrain the initial possible morphologies) and the evolutionary forces (selecting the fittest morphologies depending on conditions) in the conodont elements evolution. We proposed heterochrony as underlying mechanism for these patterns, potentially driven by oceanic temperature. Shape quantification is also used in an attempt to clarify the neogondolellids taxonomy of the early Triassic. This work demonstrates the conodont's potential as model organism to study evolution in deep time.