Cambrian mystery trace fossil

I have been puzzled by this Early Cambrian trace fossil ever since I collected it about 35 years ago while on a field trip with my paleontology class. The trace consists of two parallel grooves that show up on the bottom of a bed of slightly metamorphosed sandy siltstone. What you see is the sediment that infilled the grooves (the sediment constitutes a cast). The trace is from the Inyo Mountains, California. I wonder what kind of animal could have made this trace. Did a single animal make it while crawling over the surface of the muddy sediment? Or, did two animals crawling alongside each other make the grooves?

I have tentatively identified this trace fossil (i.e., technically speaking, an ichnofossil) as Scolicia sp.

If anyone has a better identification, please let me know via the comments option on this blog site.

Oldest fossil shells in California

The oldest known fossil shells in California are poorly preserved hollow tubes of Wyattia reedensis Taylor, 1966.  They are found in uppermost Precambrian to possibly lowermost Cambrian (see the time diagram in my last post) carbonate rocks in the Inyo Mountains of eastern California. A representative tube, as indicated in the above image by the short black arrow, is approximately 10 mm in length and 3 mm in diameter. The rock surrounding this tube contains many other, but less distinct, tubes of W. reedensis. 

Wyattia is a probable molluscan fossil and is pre-trilobite in age. Wyattia and other small-sized shells are important because they represent the oldest skeletonized faunas on Earth. These fossils occurred during an interval of geologic time between when only impressions of soft-bodied organisms have been found versus when the first shells of larger animals (e.g., trilobites) have been found.

Late Precambrian to early Cambrian Wyattia-like fossils have also been found in Esmeralda County Nevada and near Caborca in northern Sonora, Mexico.

Wyattia was named for J. Wyatt Durham (deceased), who was a professor of paleontology (study of fossils) for many years at the University of California, Berkeley.