IDYST - ISTE Seminar
As soft tissues rarely preserve in the geological record, fossil skeletons are the primary source of information on the evolution of life. What is more, the development of a mineralized skeleton has been one of the key evolutionary innovations and allowed organisms to spread into new niches. Biominerals building skeletal tissues have mechanical properties representing adaptations to these niches. Especially in the early history of life, these properties may be the main source of information about the animal's life habit, diet, and its interactions with the environment. I investigate the early evolution of phosphatic biomineralization using the extinct groups conodonts and thelodonts as models. Conodonts were the first chordates to develop a biomineralized phosphatic skeleton. Their dental tools resemble teeth functionally, but their internal structure and the mechanism of growth are unique. Over nearly 300 My of their evolution, conodont feeding apparatuses achieved stupendous morphological diversity, which is hypothesized to reflect a broad dietary, ecological and developmental variation. In order to investigate whether dietary adaptations are expressed at the ultrastructural level, I undertook a systematic characterization of the ultrastructure of conodont dental tissues. Using electron backscatter diffraction (EBSD), X-ray diffraction, small-angle neutron scattering, and atomic force microscopy, I demonstrated that conodont biomineralized tissues have a hierarchical organization, in which mesoscopic crystals are formed by nanosized crystalline units separated with an intergranular organic sheath. Nanogranular structure is emerging as a common feature of many biominerals, associated with distinct structure-relationship properties. Tracking its development across Earth history may help us understand the factors behind the evolutionary success of biomineralizing clades, such as vertebrates or mollusks.