INVESTIGATING THE HYDRODYNAMICS OF THE ENIGMATIC CARBONIFEROUS FISH, TULLIMONSTRUM GREGARIUM, WITH COMPUTATIONAL FLUID DYNAMICS (CFD)

Tullimonstrum gregarium, more commonly known as the Tully Monster, is one of the strangest creatures in the fossil record. While it was traditionally considered a problematic fossil, recent studies have firmly identified the Tully Monster as a vertebrate, tentatively as a relative of lamprey and hagfish. This may offer some insight into the Tully Monster’s ecology, but the Tully Monster’s swimming ability remains uncertain due to its strange body plan. The Tully Monster’s elongate proboscis and eyebar, for example, are unusual among vertebrates and likely affect the Tully Monster’s swimming abilities. The Tully Monster also lacks paired fins, like pectoral fins and pelvic fins, which typically allow fish to turn and stabilize their bodies. Collectively, these strange characteristics and the Tully Monster’s posteriorly concentrated musculature call the Tully Monster’s swimming mechanisms into question. Furthermore, the proboscis itself could have been held in various positions while the Tully Monster swam, and different proboscis positions would have different effects on the Tully Monster’s swimming. This study aims to investigate the hydrodynamics of these features to gain insight into the Tully Monster’s swimming ability using computational fluid dynamics (CFD). 2D simulations of the Tully Monster revealed that the eyebar and proboscis are likely key hydrodynamic features, and that the tail fin complex could have generated pressure differentials. Pressure differentials generated around the body also suggest the Tully Monster was a slow swimmer, and likely had a hydrodynamic tendency to descend in the water column. The proboscis position during swimming, however, remains uncertain.