IMPACT OF ENVIRONMENTAL STRESS ON THE MORPHOSPACE OF PLIENSBACHIAN-TOARCIAN BELEMNITES

One of the most common responses of marine ectotherms to current and past global warming is a decrease in body size. However, not much is known about how changes in early development and growth impact morphology. Understanding morphological changes of organisms (e.g., belemnites) across environmental crises in the past, could be a key to predicting future climate impacts. The Pliensbachian -Toarcian (Pli-Toa) boundary event (~183 mya) is a precursor event of the Toarcian Ocean Anoxic Event and is driven by a rapid warming, triggered by volcanic activity of the Karoo-Ferrar Large Igneous Province.

We use 3D geometric morphometrics to study the morphospace of 144 belemnites, from 5 consecutive samples across the Pli-Toa crisis in Peniche, Portugal.

Preliminary results show that two species, which also drive the decrease in body size, significantly increase in robustness across the boundary. In C. longiforma, only adult specimens increase in robustness with the warming. In P. bisulcata, juveniles show a similar trend and become even more robust into the Toarcian, while adults become rare.

The increase in robustness could indicate that warming habitats might affect slender specimens disproportionately. However, causes could also be indirect consequences of warming, like starvation or hypercalcification. We conclude that the warming habitat at the Pli-Toa boundary in Peniche impacts growth of two belemnite species at different stages in their development. Therefore, we suggest that it is important to not only take taxonomy, but also ontogeny into account, when studying impacts of environmental stressors on morphological variables of organisms.