Mark Wilson February 12th, 2012
It is pretty obvious what made this excellent trace fossil: an asteroid echinoderm. (The term “asteroid” sounds odd here, but it is the technical term for a typical sea star.) The above is Asteriacites stelliformis Osgood, 1970, from the Chagrin Shale (Upper Devonian) of northeastern Ohio.
We can tell that it was made by a sea star burrowing straight down into the sediment because it has faint chevron-shaped marks in the rays made by tube feet as they moved sediment aside. The mounds of excavated sediment can be seen between the rays at their bases. This tells us that we are not looking at an external mold of a dead sea star, but instead its living activity. This is what a trace fossil is all about.
The ichnogenus Asteriacites was named by von Schlotheim in 1820. We profiled him earlier with the genus Cornulites. The author of Asteriacites stelliformis was Richard G. Osgood, Jr., my undergraduate advisor and predecessor paleontologist at The College of Wooster.
Richard Osgood, Jr., was born in Evanston, Illinois, in 1936. He went to Princeton for his undergraduate degree (I still remember his huge Princeton ring) and received his Ph.D. from the University of Cincinnati. He worked for Shell Oil Company in Houston just prior to joining the Wooster faculty in 1967. He was one of the pioneers of modern ichnology (the study of trace fossils), naming numerous new ichnotaxa and providing ingenious interpretations of them. At least one trace fossil was named after him: Rusophycus osgoodii Christopher, Stanley and Pickerill, 1998. Dr. Osgood died in 1981 in Wooster. He was an inspiration to me and many other Wooster geology students during his productive career, which was all too short.
Osgood, R.G., Jr. 1970. Trace fossils of the Cincinnati area. Palaeontographica Americana 6: 281-444.
Schlotheim, E.F. von. 1820. Die Petrfactendunde auf ihrem jetzigen Standpunkte durch die Beshreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzernreichs der Vorwelt erläutert 1-457.
Stanley, D.C.A. and Pickerill, R.K. 1998. Systematic ichnology of the Late Ordovician Georgian Bay Formation of southern Ontario, eastern Canada. Royal Ontario Museum Life Sciences Contribution 162, 56 pp., 13 pl. Toronto.