The above picture is the bottom of a Cambrian Rusophycus from the Inyo Mountains, central California. The burrow is 10 cm in length. Scratch marks made by the trilobites legs are visible on the bottom of the burrow.
Ahh, finally we get to a truly exceptional specimen of Rusophycus. It is undoubtedly the best specimen I have ever seen. It is preserved three-dimensionally (8.5 cm long, 3.5 inches) and is of Cambrian age from the Salt Spring Hills, eastern California. The above picture is the bottom view, which shows the scratches made by the legs of the trilobite. The specimen is a plaster replica of the actual specimen, which is now in a museum collection. I painted the plaster replica so as to make it look more like the actual specimen.
This is a side view of the same specimen shown above. The bottom of the burrow is at the top of the picture. I painted the antennae red, so you can readily see them. The fact that the antennae are visible indicates that the remains of the trilobite that made this resting trace are within the burrow, thereby proving the trilobite made this burrow. In situ (in place) specimens of trilobites in their burrows are very rare.