LIFE'S A DRAG - A CAMBRIAN GIANT HOLDS FAST

A study of abundant trace fossils on sandstone slabs from the Lower Cambrian (530 Ma) Gog Formation of The Monarch, near Banff, revealed unusual linear structures. These appear as subparallel scratch marks on which even smaller longitudinal striations occur. Statistical analysis shows that the marks have a preferred orientation and that they are sub-equally spaced. Preferred alignment suggests that the striations arose as drag marks in currents rather than from behavioural activity. Regular spacing, length of the marks, and the longitudinal mini-striae (perhaps gill marks) indicate the striations were created by a single type of creature, probably an arthropod. This creature may have been an exceptionally large trilobite or an unknown arthropod perhaps akin to the giant Tegopelte gigas from the middle Cambrian Burgess Shale. However, no trilobite feeding traces preserved in the Gog are large enough to proportionally match the drag marks. We propose that the linear structures are drag marks of a biramous limb which are a result of the creature trying to prevent itself from being moved laterally by a current. This hypothesis is consistent with preserved interference ripple marks which indicate a high energy, shallow marine environment during Gog deposition.