Archive for September 4th, 2015

Wooster’s Fossil of the Week: A mystery fossil for my Invertebrate Paleontology students

September 4th, 2015

1 Stereolasma singleAt the beginning of my Invertebrate Paleontology course I give each student a fossil to identify by whatever means necessary. I challenge them to take it down to the species level, and tell me its age and likely place of collection. The fossil this year is shown above: the rugose coral Stereolasma rectum (Hall, 1843) from the Middle Devonian of New York. I collected the specimens on my western New York adventure last month from the Wanakah Shale Member of the Ludlowville Formation at Buffalo Creek in Erie County. (There were a lot of them! This coral is so common that you can buy them online at science supply stores.)

The corals I collected were well weathered on the Devonian seafloor. You can see some evidence of this in the exterior which shows opened tunnels of borings. They were not appreciably weathered on the outcrop because they were directly excavated from the shale matrix.
2 Stereolasma cross section 585This is a cross-section through one of the S. rectum specimens. The internal radiating calcitic partitions (septa) are well preserved by clear calcite cement. There appear to be at least two generations of sediment that penetrated into the interior after the death of the polyp. The posthumous events affecting these corals may be more interesting than their life histories.

That awkward species name comes from the Latin rectus for “straight”. The anatomical rectum that we all know well comes from the same root but is based on a misconception by early anatomists that the terminal part of the large intestine in mammals is straight. It’s not, as a Google search will quickly show you. (I decided against including an image.)
3 Wanakah coralsReferences:

Baird, G.C. and Brett, C.E. 1983. Regional variation and paleontology of two coral beds in the Middle Devonian Hamilton Group of Western New York. Journal of Paleontology 57: 417-446.

Brett, C.E. and Baird, G.C. 1994. Depositional sequences, cycles, and foreland basin dynamics in the late Middle Devonian (Givetian) of the Genesee Valley and western Finger Lakes region. In: Brett, C.E., and Scatterday, J., eds., Field trip guidebook: New York State Geological Association Guidebook, no. 66, 66th Annual Meeting, Rochester, NY, p. 505-585.

Busch, D.A. 1941. An ontogenetic study of some rugose corals from the Hamilton of western New York. Journal of Paleontology 15: 392-411.

Stumm, E.C. and Watkins, J.L. 1961. The metriophylloid coral genera Stereolasma, Amplexiphyllum, and Stewartophyllum from the Devonian Hamilton group of New York. Journal of Paleontology 35: 445-447.