Wooster’s Fossil of the Week: A scolecodont from the Upper Ordovician of the Cincinnati region

May 4th, 2014

Cincinnatian scolecodontThis tiny but fearsome jaw is known as a scolecodont, and they are fairly common in the Cincinnatian rocks (Upper Ordovician) in the tri-state area of Ohio, Kentucky and Indiana. The label on this particular specimen does not indicate the exact locality or stratigraphic unit, but it does give a taxonomic name: “Nereidavus varians Grinnell 1877″. More on that below.

Scolecodonts are the jaws of extinct polychaete annelid worms. They are known from the Cambrian right through the Recent, so we’re pretty sure what their functions were: grabbing prey and pulling it into the gullet of the worm. They are made of a very tough chitin (an organic material much like our fingernails) and survive well the vicissitudes of fossilization. I ran across them often when I studied conodonts, which they superficially resemble.

Polychaete mouthThe Telegraph, of all places, has some amazing SEM images of the scary end of living jawed polychaetes, one of which is shown above. (I think they colored it to look like it has blood on its teeth.) Our Ordovician jaw easily fits into this functional model.

For much more on scolecodonts, Olle Hints has a superb website devoted just to these critters, and Rich Fuchs has a very useful page on the Cincinnatian varieties.

Now as for the name of our specimen, it appears that the taxonomy of Ordovician scolecodonts is in a bit of disarray. Nereidavus Grinnell, 1877, is, according to Bergman (1991) and Eriksson (1999), a nomen dubium (dubious name) because the holotype (single primary type specimen) of the type species is lost. That specimen was from Cincinnatian strata, then referred to as “Lower Silurian”. The paratype (sort of a spare type specimen) is N. varians, the same name on the label of our specimen. Eriksson considered that species to be in the genus Ramphoprion Kielan-Jaworowska, 1962. A true diagnosis of our specimen would involve extracting it from the matrix and looking at it its dorsal (oral) surface, but that’s not going to happen. I’m plenty happy just leaving this fossil as Ramphoprion sp.

Kielan-JaworowskaThe paleontologist who named the scolecodont genus Ramphoprion is the famous and incredibly accomplished Zofia Kielan-Jaworowska (above). She is best known for her pioneering work on dinosaur-bearing deposits in Mongolia in the 1960s, but she has worked on many fossil groups from trilobites to mammals. Kielan-Jaworowska (born in 1925) received her Masters Degree in zoology and a doctorate in paleontology (aren’t many of those now) at Warsaw University. She became a professor there and was later the first woman to serve on the executive committee of the International Union of Geological Sciences. I read her 1974 book Hunting for Dinosaurs in college as an adventure tale with a strong narrative framework of science. It was inspirational, and it convinced me that paleontology was the coolest science.

References:

Bergman, C F. 1991. Revision of some Silurian paulinitid scolecodonts from western New York. Journal of Paleontology 65: 248–254.

Eriksson, M. 1999. Taxonomic discussion of the scolecodont genera Nereidavus Grinnell, 1877, and Protarabellites Stauffer, 1933 (Annelida: Polychaeta). Journal of Paleontology 73: 403-406.

Eriksson, M. and Bergman, C.F. 2003. Late Ordovician jawed polychaete faunas of the type Cincinnatian Region, U.S.A. Journal of Paleontology 77: 509-523.

Grinnell, G.B. 1877. Notice of a new genus of annelids from the Lower Silurian. American Journal of Science and Arts 14: 229–230.

Hints, O. and Eriksson, M.E. 2007. Diversification and biogeography of scolecodont-bearing polychaetes in the Ordovician. Palaeogeography, Palaeoclimatology, Palaeoecology 245: 95-114.

Kielan-Jaworowska, Z. 1962. New Ordovician genera of polychaete jaw apparatuses. Acta Palaeontologica Polonica 7: 291-325.

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