Institute of Applied Geoscience (IAG)
Upcoming Earth and Environment seminars

Research Seminars

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Body-size reductions during mass extinction: local environmental fluctuations or global evolutionary perturbations?

Date: Friday 27th April

Time: 15:00 to 16:00

Presenter: Kenneth De Baets, Geozentrum Nordbayern

Location: SEE Seminar Rooms 1&2, 8.119

Body size, being well accessible in fossils, has been a research focus for generations of paleontologists. Most studies focus on either long-term evolutionary trends within or across lineages or on short-term variations in the context of evolutionary crises. However, to properly understand it considerable data on background changes in body size needs to be compiled and their relationship with environmental changes.

We study size changes in belemnite assemblages from the Pliensbachian-Toarcian crisis. To avoid potential confounding factors of anoxia, we initially focused on efforts on Peniche where there is evidence for a rapid temperature increase  and volcanism without clear development of black shales across the Pliensbachian-Toarcian boundary. Our results show the largest size decrease in belemnite assemblages across the Pliensbachian-Toarcian boundary when compared with samples before and after the crisis. It seems to be mainly driven by decrease in adult size of the most common belemnite taxon.

To evaluate how this oft-cited Lilliput effect compares acroos spatio-temporal scales, we compiled more than 6000 interval-to-interval changes in marine taxa. Interestingly, negative changes are significantly more pronounced during changes from background to crises intervals than in other combination of background-crisis-survival-recovery intervals. However, dwarfing is not necessarily evidence for warming-induced crises, since it occurs both in the aftermath of hyperthermals (e.g., end-Permian, Pliensbachian-Toarcian crisis) as well as hypothermals (e.g., end-Ordovician, end-Cretaceous). There is a significant dependency on the responsiveness among taxonomic groups – ammonoids, bivalves and benthic foraminifers are more responsive than other groups. Further research is necessary to investigating the underlying mechanisms driving body size changes in various levels of organisation (assemblages, population or individual growth).