Is the relative thickness of ammonoid septa influenced by ocean acidification, phylogenetic relationships and palaeogeographic position?

Abstract

The impact of increasing atmospheric CO2 and the resulting decreasing pH of seawater are in the focus of current environmental research. These factors cause problems for marine calcifiers such as reduced calcification rates and the dissolution of calcareous skeletons. While the impact on recent organisms is well established, little is known about long-term evolutionary consequences. Here, we assessed whether ammonoids reacted to environmental change by changing septal thickness. We measured the septal thickness of ammonoid phragmocones through ontogeny in order to test the hypothesis that atmospheric pCO2, seawater pH and other factors affected aragonite biomineralisation in ammonoids. Particularly, we studied septal thickness of ammonoids before and after the ocean acidification event in the latest Triassic until the Early Cretaceous. Early Jurassic ammonoid lineages had thinner septa relative to diameter than their Late Triassic relatives, which we tentatively interpret as consequence of a positive selection for reduced shell material as an evolutionary response to this ocean acidification event. This response was preserved within several lineages among the Early Jurassic descendants of these ammonoids. By contrast, we did not find a significant correlation between septal thickness and long-term atmospheric pCO2 or seawater pH, but we discovered a correlation with palaeolatitude.

Stability–Maneuverability Tradeoffs Provided Diverse Functional Opportunities to Shelled Cephalopods

“…That is, these cephalopods would have reduced energy expenditure and self-generated wake during rotation while having 360° access to closely surrounding prey ( Peterman and Ritterbush 2022 ; Peterman et al 2022 ). In addition to these physical properties, other factors are likely involved in selection (other functional/morphogenetic factors, Kröger 2005 ; Tendler et al 2015 ; Parent et al 2020 ; Peterman et al 2021 ; Hebdon, Polly et al 2022 ; Weber et al 2022 ; competition, Ritterbush 2016 ). While the endmembers of the planispiral morphospace ( Ritterbush and Bottjer 2012 ) represent extreme cases, the majority of cephalopods occupied spaces in between.…”