Testing hypotheses of pteraspid heterostracan feeding using computational fluid dynamics
2023
Grohganz, Madleen | Ferrón, Humberto G. | Johanson, Zerina | Donoghue, Phillip C.J.
The early evolution of vertebrates in their ecological context is often depicted as a transition from passive to more active feeding behaviors. However, understanding the feeding ecology of extinct stem-gnathostomes, particularly heterostracans, which are among the earliest, has relied heavily on speculative interpretations. Pteraspidiform heterostracans featured a feeding apparatus comprising rod-like oral plates with rows of denticles, previously thought to aid in suspension feeding. Here, we challenge this notion using computational fluid dynamics. By simulating water flow around 2D models with rows of denticles oriented both rostrally and reversed, we investigate if these orientations facilitate hydrodynamic adaptations for suspension feeding. Our analyses reveal that regardless of denticle orientation, the flow, velocity, and vorticity patterns are consistent. Recirculation patterns, along with high velocity and vorticity, concentrate directly on top of and between the denticles. Consequently, we refute the hypothesis that denticle orientation facilitates recirculation associated with suspension feeding. Instead, it is plausible that the denticles served to prevent material from becoming lodged between the plates.
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