Stokes noticed several curved grooves preserved  alongside the tracks, and he believed these grooves were likely made by either that 4th  digit or the pteroid dragging along the ground.

斯托克斯注意到沿着轨道保留了几个弯曲的凹槽，他认为这些凹槽很可能是由第 4 指或沿着地面拖动的翼状体形成的。