16 Paleontology of North America
Added from Discipline submissions.
Monday, 9 March 2026
1:30 PM - 4:30 PM
RCC, 106
Investigating Tullimonstrum gregarium’s Proboscis using Two-Dimensional Computational Fluid Dynamics (CFD)
Paper number: 16-11
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM
Authors
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Victoria McCoyUniversity of Wisconsin - Milwaukee, Milwaukee, Wisconsin
Abstract
Tullimonstrum gregarium, a charismatic aquatic organism from the Late Carboniferous Mazon Creek lagerstätte in northeastern Illinois, has been the subject of debate for decades. Tullimonstrum gregarium has been a classic example of a problematic taxa, but recent work has pointed towards a chordate affinity for this strange organism. Concurrently, work on the Mazon Creek fossil site has identified three distinct faunal assemblages, each representing a different portion of the Late Carboniferous deltaic environment preserved in the Mazon Creek’s concretions. Ecological interpretations have been difficult at the Mazon Creek, as the majority of Mazon Creek fossiliferous concretions were collected from mining spoil piles outside of their stratigraphic context. In the absence of stratigraphic context, broad placement of a fossil into one of the three Mazon Creek assemblages can be paired with interpretations of an organism’s functional abilities to elucidate that organism’s position in the aquatic Mazon Creek environment. Specifically, modeling aquatic organisms using computational fluid dynamics (CFD) can constrain an organism’s position within the water column and can inform hypotheses related to predator-prey interactions or feeding. This is particularly useful when interpreting Tullimonstrum gregarium, which has a suite of strange features with unclear function in the context of swimming. Specifically, Tullimonstrum gregarium’s muscles are concentrated near the posterior of the body, similar to tail-propelled fish. This suggests that Tullimonstrum was a tail-propelled swimmer, yet it lacks most of the paired fins fish use to control their movement while using their tails for propulsion. We hypothesize that Tullimonstrum’s proboscis could be used for braking or turning by interrupting flow around the body, similar to the function of paired fins in modern fish. To investigate this, two-dimensional lateral and dorsal models of Tullimonstrum were generated with the proboscis placed in various anatomically feasible positions. These models were then used in CFD simulations in the OpenFoam software to analyze the effect of proboscis position on the flow around the body. Simulation results match predictions that movement of the proboscis disrupts flow around the body, which could be used for braking or pivoting.
Geological Society of America Abstracts with Programs. Vol. 58, No. 1
doi: 10.1130/abs/2026SE-411794
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