Environmental and biotic controls on conodont body size and teeth morphology as proxies for their feeding ecology
Final Report Abstract
Several new tools have been tested and developed to establish the trophic ecology of conodonts, extinct marine vertebrates which played a substantial role in Palaeozoic and Triassic ecosystems. Using their biomineralized dental elements, histological, chemical, and morphological proxies have been assessed to establish their position in the trophic network. For this purpose, museum collections of Silurian conodonts from Gotland, Sweden, have been curated and compiled into Paleobiology Database. Furthermore, additional fieldwork has been conducted in Gotland and in Midland Platform, UK. The main findings are: conodont size and the composition of their communities (alpha and beta diversities) are primarily controlled by their position along the onshore-offshore gradient and, accordingly, by the depositional environment in which they lived. A new method of visualizing growth increments within the crown tissues of conodont elements has been developed. It allowed the identification of a change in the feeding mode during ontogeny, from lower in the trophic chain to higher. The trophic shift associated with growing is manifested in the appearance of periodic wear surfaces in the tissue. This imaging method resolved previous controversies concerning the mode of growth in conodonts, confirming that they were the only vertebrates capable of repair and renewed growth in vivo throughout their lifetime. The sclerochronological reconstructions of the trophic shift were confirmed using the Sr/Ca and Ba/Ca proxy for the trophic position. The values of these proxies differ systematically between taxa within the same assemblages, demonstrating that trophic diversity of conodonts matched their morphological diversity. High Sr content typical of a position low in the trophic chain correlates closely with the early stage of life and the lack of wear surfaces. However, the project has shown that systematic differences in the values of these proxies exist between different tissues in conodonts as well as in thelodonts, requiring researchers to account for the histology and crystallography, as well as contemporary seawater composition, in using the new proxy. The project established new histological techniques and chemical proxies for reconstructing trophic relationships in fossil ecosystems. It also provided evidence for the wide range of trophic niches occupied by conodonts and their diverse role in the emergence of marine interaction networks.
Publications
- (2018). Harnessing stratigraphic bias at the section scale: conodont diversity in the Homerian (Silurian) of the Midland Platform, England. Palaeontology, 61(1), 57-76
Jarochowska, E., Ray, D. C., Röstel, P., Worton, G., & Munnecke, A.
(See online at https://doi.org/10.1111/pala.12326) - (2018). Wear, tear and systematic repair: testing models of growth dynamics in conodonts with high-resolution imaging. Proceedings of the Royal Society B: Biological Sciences, 285(1886), 20181614
Shirley, B., Grohganz, M., Bestmann, M., & Jarochowska, E.
(See online at https://doi.org/10.1098/rspb.2018.1614) - (2020). High-resolution correlation of the Homerian carbon isotope excursion (Silurian) across the interior of the Midland Platform (Avalonia), UK. Geological Magazine, 157(4), 603-620
Ray, D. C., Jarochowska, E., Röstel, P., Worton, G., Munnecke, A., Wheeley, J. R., & Boomer, I.
(See online at https://doi.org/10.1017/S0016756819001146) - (2020). Vertebrate remains and conodonts in the upper Silurian Hamra and Sundre formations of Gotland, Sweden. GFF, 142(1), 52-80
Bremer, O., Jarochowska, E., & Märss, T.
(See online at https://doi.org/10.1080/11035897.2019.1655790)
