Modelling the soft-body mechanisms of snake tongues, larval fish and primitive chordates

We developed a simulation model for soft tissues that undergo large deformations. The mass distribution of the tissue is represented by a series of point masses that are interconnected by tensile elements. The tensile elements not only can be given nonlinear properties, but also muscular characteristics such as active force production, and length- and velocitydependence of force. In addition, fluid-pressure gradients are taken into account as driving forces on the point masses. From the initial geometry, internal fiber arrangement and time-dependent activation of various muscle groups, the model computes the deformation of the soft body in a forwarddynamics manner. The model was used for the study of the design and control of soft bodies and movement reconstructions of extinct soft-bodied animals. Predicted protrusion and flicking motions of the tongue in snakes resembled actual movements that were recorded with 3D high-speed video. The model also predicted the cambering of the finfold of larval fish observed in high-speed movies. Finally, the model was also used to reconstruct the body mechanics of the fossil, Cambrian chordate, Haikouella. Given Haikouella’s reconstructed muscle architecture and the large ventrally positioned notochord, and making several assumptions about the material properties of the various tissues, the model predicts that Haikouella could effectively bend its body. Haikouella most likely used traveling body waves to propel itself through the water.