THE GOOD, THE BAD, AND THE HYPOXIC: INVESTIGATING THE RESPONSE OF INARTICULATE BRACHIOPODS TO LOW-OXYGEN CONDITIONS

Approximately 251.9 million years ago, three to five million cubic kilometers of the Siberian flood basalts were initiated. The ensuing end-Permian mass extinction resulted in the greatest animal biodiversity loss in the history of life, across both the terrestrial and marine spheres. Lingulids exhibited remarkably high abundance in the wake of this catastrophe, resulting in their establishment as a ‘disaster taxa.’ However, there has been limited physiology work to explain the factors responsible for this observation.

We ran respirometry experiments on inarticulate brachiopods (G. pyramidata) and bivalves (M. campechiensis) to investigate the impact of hypoxia on these invertebrates. We then calibrated the metabolic index parameters to determine if and how inarticulate brachiopods, articulate brachiopods, and bivalves differentially respond to low O₂ levels and high temperatures. We found that lingulids are more sensitive to higher temperatures, but less sensitive to hypoxia than bivalves. This aligns with earlier work, which suggests that bivalves tolerate high temperatures better than brachiopods, but have lower tolerance for hypoxia. Articulate brachiopods (T. transversa), on the other hand, were more sensitive to hypoxia and temperature than both inarticulates and bivalves; this could explain lingulids’ comparatively high abundance in Lower Triassic strata with geochemical and sedimentary indicators of low-oxygen conditions. Ultimately, this study could help improve our understanding of the role aerobic physiology may play in driving extinction selectivity differences, during climate perturbations throughout Earth history and today.