This is one of my favorite trace fossils. Rusophycus pudicum Hall, 1852, is its formal name. It was made by a trilobite digging down into the seafloor sediment back during the Ordovician Period in what is now southern Ohio. It may have been hiding from a passing predator (maybe a eurypterid!), just taking a “rest” (what I learned in college), or maybe looking for worms to eat. (There is another example on this blog from the Cambrian of western Canada.)
Rusophycus is always the first trace fossil I introduce in the Invertebrate Paleontology course because it is simple in form and complex in interpretation. It shows that a relatively straightforward process (digging down with its two rows of legs) can have had several motivations. Rusophycus even shows that more than one kind of organism can make the same type of trace. Rusophycus is also found in the Triassic, long after trilobites went extinct. (These were likely made by horseshoe crabs.) It is also good for explaining the preservation of trace fossils. The specimen above is “convex hyporelief”, meaning it is on the bottom of the sedimentary bed and convex (sticking out rather than in). This is thus sediment that filled the open trilobite excavation.
Trilobites making Rusophycus (from http://www.geodz.com/deu/d/Trilobita).
James Hall (1811–1898) named Rusophycus pudicum in 1852. The image of him above is from shortly before his death (photograph credit: The American Monthly Review of Reviews, v. 18, 1898, by Albert Shaw). He was a legendary geologist, and the most prominent paleontologist of his time. He became the first state paleontologist of New York in 1841, and in 1893 he was appointed the New York state geologist. His most impressive legacy is the large number of fossil taxa he named and described, most in his Palaeontology of New York series.
James Hall is in my academic heritage. His advisor was Amos Eaton (1776-1842), a self-educated geologist (he learned it by reading in prison!). One of James Hall’s students was Charles Schuchert (1856-1942), a prominent invertebrate paleontologist. Schuchert had a student named Carl Owen Dunbar (1891-1979) — Schuchert and Dunbar were coauthors of a famous geology textbook. Dunbar had a student at Yale named William B.N. Berry (1931-2011), my doctoral advisor. Thus I feel an intellectual link to old man Hall above.
Baldwin, C.T. 1977. Rusophycus morgati: an asaphid produced trace fossil from the Cambro-Ordovician of Brittany and Northwest Spain. Palaeontology 51: 411–425.
Donovan, S.K. 2010. Cruziana and Rusophycus: trace fossils produced by trilobites … in some cases? Lethaia 43: 283–284.
Hall, J., Simpson, G.B. and Clarke, J.M. 1852. Palaeontology of New York: Organic remains of the Lower Middle Division of the New-York System. C. Van Benthuysen, New York, 792 pages.